Collating several meteor orbit catalogues derived from photographic, video and
radar systems, _Hajdukova et al._ (2020) concluded that there was no
convincing evidence of any interstellar meteors being detected in 25 years of
data covering many thousands of objects. That said, a careful analysis of
$4\times 10^{5}$ meteors detected by the Canadian Meteor Orbit Radar led
_Froncisz et al._ (2020) to identify 5 possible interstellar meteors. We note
that this possible interstellar fraction of $\sim$1 in 80,000 meteors is
significantly lower than the $\sim$1 in 900 implied for the current CNEOS
fireball database.

It is clear from these latter studies that measurement uncertainties are
extremely important in interstellar meteor identification, due to the short
timespan over which the observations are obtained. Until such a time that a
quantitative description of the uncertainties on the DoD satellite
measurements is forthcoming (and indeed their actual values), some uncertainty
unfortunately still remains concerning an interstellar origin for CNEOS
2014-01-08. It therefore follows that the pursuit of interstellar meteor
detections with quantifiable uncertainties is a highly worthwhile endeavor.

###  6.5 ISO impact hazard

As reported in the Planetary Decadal survey (_National Academies of Sciences
and Medicine_ , 2022), as of 2021 about 95% of the NEOs greater than 1 km in
diameter have been found. These objects are capable of causing global effects
upon impact. Objects that are larger than 140 m in diameter can cause regional
destruction and to date, only about 33% of these have been discovered.
Estimates show that there might be more than 105 objects $\geq$50 m in
diameter which could cause destruction on urban scales, and less than 2% of
these have been found. In 2005 Congress directed NASA to find 90% of all NEOs
larger than 140m, and to date this directive has not been met. Once it is met,
the threat from impacts from near earth asteroids will be minimized, but this
will not address the risk from objects on long period Oort cloud comet (OCC)
trajectories. It is likely that OCCs are responsible for most of the very
large impacts on Earth (_Jeffers et al._ , 2001).

The typical NEO encounter velocity peaks around 15 km/s, with a range up to 40
km/s (_Heinze et al._ , 2021), however the encounter velocities for OCCs will
typically be around 54 km/s ranging from 16 up to 72 km/s (_Jeffers et al._ ,
2001). ISO trajectories will be very similar to those of OCCs, but the
encounter velocities can be even higher. At the time of close approach to the
Earth on 2017 Oct. 14, the relative velocity of 1I/‘Oumuamua with respect to
the Earth was 60.3 km/s. It passed within 63 Earth-moon distances and we did
not and could not have discovered it until after it had passed. Objects like
1I/‘Oumuamua which are on OCC-like orbits but which do not have any detectable
activity, have small nuclei, and low albedo (such as the Manx comets, see
_Meech et al._ 2016) are particularly dangerous because they will be harder to
detect. _Heinze et al._ (2021) also noted that there is a larger bias than
expected against finding small fast moving objects because of the streak
length on the detector, so inactive ISOs will be particularly hard to find and
we are more likely to be missing more of these.

These OCC and ISO trajectories will be distributed across a wide range of
inclinations. As discussed in §7.3.1, the powerful new Vera C. Rubin
Observatory (Rubin) Legacy Survey of Space and Time (LSST) will begin in
mid-2025. There is a concerted effort to optimize the survey effort to benefit
solar system science, including detection of OCCs, NEOs and potentially
hazardous objects (_Schwamb et al._ , 2023). 1I/‘Oumuamua was discovered at
1.22 au moving at a rate of 6.2∘ per day, i.e. typical of a faint nearby NEO
that the LSST will be optimized to detect.

##  7 THE NEXT DECADE OF EXOCOMET AND ISO STUDIES – WHAT DON’T WE KNOW?

###  7.1 Exocomet Systems

####  7.1.1 Probing outer exocomet populations

Current and under-construction facilities should lead to significant advances
in the field of exocomet science. An important area of study will be to
understand the dynamical evolution of exocomets in planetary systems, which
requires both high angular resolution and sensitivity at dust-emission
wavelengths. Near to mid-IR dust imaging will take place with the 6.5m James
Webb Space Telescope (JWST) , the 39-m ESO Extremely Large Telescope (ELT)
with its MICADO and METIS cameras (_Brandl et al._ , 2010; _Davies et al._ ,
2018), and large, deep ALMA surveys such as the ongoing ARKS (The ALMA survey
to Resolve exoKuiper belt Substructures, Marino et al. in prep.). These will
deliver unprecedentedly detailed images of dust emission from exocometary
belts, revealing planet-belt interaction and allowing us to infer the
dynamical fate of exocomets within belts, be it ejection, inward scattering,
or survival within the belt.

Gas observations offer a unique window into exocometary compositions in young
planetary systems just after formation. Near- to mid-IR spectroscopy with JWST
combined with ground-based near-IR high-resolution spectrographs (like the
newly-installed CRIRES+ instrumentation on the ESO Very Large Telescope and
later the ELT+HARMONI) will be used to probe ro-vibrational transitions of new
molecules undetectable at mm wavelengths, such as CO2, CH4 and of course H2O
and its photodissociation product OH. This will constrain exocometary
molecular gas compositions within outer belts, with the potential to confirm
the gas origin, determine the physical release mechanism, and ultimately the
ice composition of young exocomets - a missing evolutionary link between outer
protoplanetary disks and solar system cometary/KBO compositions.

In addition, ALMA CO and C I line imaging will constrain the radial and
vertical distribution and hence the evolution of gas within exocometary belts;
this will be combined with detail kinematic analysis, thanks to ALMA’s maximum
spectral resolution, to reveal the environmental conditions (temperature, bulk
density) of the gas, and evaluate the dynamical influence of planets on the
evolution of exocometary gas.

####  7.1.2 Probing the inward transport of exocomets

The highest priority for the future of exocomets in the inner regions should
be to expand the number of detections and detected systems - currently
dominated by $\beta$ Pic - and study their compositions and dynamics as they
enter the innermost regions of a planetary system. This will enable us to
probe their formation location and the mechanism leading to their inward
transport - with the potential of linking their origin to detected exoplanets,
and imaged populations of exocomets in outer belts.

JWST is especially sensitive to warm dust emission in the interior regions of
nearby systems, either through its direct imaging or aperture masking modes,
and this can be used to set limits on inward scattering and transport of icy
exocomets from the outer belt towards the terrestrial region (_Marino et al._
, 2018a). The Roman Space Telescope is a 2.4-m wide-field optical and near-IR
facility, currently planned to launch on 2027. Its coronagraph instrument is
also expected to expand the number of systems with exozodiacal light
detections in the terrestrial planet region (_Douglas et al._ , 2022). Imaging
of exozodiacal dust may for the first time also be possible around the nearest
stars with the ELT (_Roberge et al._ , 2012).

The identification and confirmation of more $\beta$ Pic-like systems requires
high resolution echelle spectrographs with large aperture telescopes to
provide high signal-to-noise per wavelength bin. Observations with new high-
resolution spectrographs on the ELT such as ANDES (_Maiolino et al._ , 2013)
and METIS (_Brandl et al._ , 2010) will exploit the ELT’s large collecting
area with their high spectral (R$\sim$100,000) resolution and wide wavelength
coverage. This will allow more sensitive searches for absorption in edge-on
systems, both from narrow, stable gas at the stellar velocity and variable
red- and blue-shifted features from exocometary gas. Monitoring observations
looking for high-velocity exocomet features should aim to cover volatiles as
well as metallic atomic species across a broad wavelength range, as one of the
highest priorities is to understand the nature and volatile content of star-
grazing exocomets.

Finally, continued exploration of TESS and CHEOPS stellar light-curves to look
for asymmetric exocomet transits are likely to lead to new discoveries. These
will be further supported by the PLATO transiting exoplanet mission (_Rauer et
al._ , 2014), with its factor $\sim 5$ increased photometric accuracy over
TESS, currently scheduled for launch in 2026. This will contribute to
understanding the occurrence rate of star-grazing exocomets around large
samples of stars, pushing towards smaller transits.

###  7.2 Galactic evolution of ISOs

####  7.2.1 Galactic effects on ISOs

In §4.2 we saw that ISOs experience various influences from the environment in
the form of thermal heating and exposure to radiation and particles of various
kinds. The question is whether ISOs also affect the environments they are
passing through. The discovery of 1I/‘Oumuamua taught us that the ISM contains
not only gas and dust but that ISOs are a natural third component of the ISM.

ISOs also pass through molecular clouds (see section 4.3), with young ISOs
more likely to make such an experience than older ones (_Pfalzner et al._ ,
2020). Such a cloud passage might alter not only the ISO surface and structure
but also the direction of their path, while at the same time decelerating or
accelerating them. Depending on the size of the actual molecular cloud
$10^{19}-10^{20}$ ISOs reside in them at any time. Being so small in mass,
their individual effect is negligible, but it could be different if co-moving
streams of ISOs pass through molecular clouds.

However, although every ISO travels through the ISM, certainly not every ISO
passes through a molecular cloud and even a protoplanetary disk. However, the
probability of ISOs passing through molecular clouds is surprisingly high. In
the solar neighborhood, an ISO spends $\approx$ 0.1%-0.2% of its journey
passing through molecular clouds (_Pfalzner et al._ , 2020). This value
increases for young ISOs close to the Galactic center. In comparison, passing
through an existing protoplanetary disk is a much rarer event due to its much
smaller cross-section. Nevertheless, _Grishin et al._ (2019) estimate that at
least 104 ISOs larger than 1 km cross any protoplanetary disk around field
stars, with the number increasing to 105 for star cluster environments.

Under certain conditions, molecular clouds collapse and form stars. It seems
that ISOs take part in this process to some extent. This would mean that ISO
could become concentrated in collapsing molecular clouds (_Pfalzner et al._ ,
2021b). However, these simulations indicate that there is a competitive
capture process at work that favors the capture of ISOs by massive star
clusters.

In the current planet formation scenario, there exist some difficulties in
proceeding from m-sized to km-sized objects (see §2.3). It has been suggested
that ISOs might easily overcome the meter-sized growth barrier by acting as
seeds to catalyze planet formation. Two different scenarios have been
suggested. _Grishin et al._ (2019) theorize that ISOs could be captured from
the local star formation region into the disks surrounding young stars .
Alternatively, _Pfalzner and Bannister_ (2019) propose the ISOs in the ISM
taking part in molecular cloud collapse would become a natural component of
the forming disk, without the need for additional capture. They give a first
conservative estimate of the order 1011 ISOs typically being incorporated into
forming star-disk systems. _Moro-Martín and Norman_ (2022) found a similar
total number when considering metre-scale ISOs and larger, but also noted the
number in the disk could increase by 2-3 orders of magnitude in cluster
environments. If ISOs take part in cloud collapse leading to star formation,
this would also mean that ISOs are incorporated into forming stars. The
question is how many ISOs end up in stars?

When ISOs pass through molecular clouds and are captured in planet-forming
disks, they can be affected by these environments. Possible mechanisms are
devolatilization and erosion. Both will lead to changes in the ISO size
distribution. Whether the ISOs are altered depends primarily on the gas/dust
density, which increases from an ISM environment to molecular clouds and
protoplanetary disks.

Finally, _Do et al._ (2018) point out that exo-Oort clouds around stars that
produce supernovae will be irradiated and lose surface volatiles, but the
exocomets there will survive. As they then drift away from the supernova
remnant they will form a natural population of devolatilized ISOs, possibly
somewhat similar to 1I/‘Oumuamua. However supernovae are rare events, and such
ISOs should not form a major component of the population.

####  7.2.2  ISO effects on the galaxy

Over the last four years, it has become apparent that ISOs are a natural
component of molecular clouds. The question is whether the presence of the
huge number of low-mass ISOs does “contaminate” star forming regions. This
depends on the mass of the ISOs present in molecular clouds, but also on the
different chemistry between star forming systems and on whether ISOs are
evenly spread or come in streams from their parent systems.

So far this question has been studied more from the perspective of individual
already forming planetary systems. This question of whether material can be
spread from one planetary system to another is of long standing interest
(_Valtonen and Innanen_ , 1982; _Melosh_ , 2003; _Adams and Spergel_ , 2005;
_Brasser et al._ , 2006). More recently, estimates of the likelihood of ISO
capture events have been performed for the early phase in young star-forming
clusters and the local galactic neighborhood (_Hands et al._ , 2019;
_Portegies Zwart_ , 2021; _Napier et al._ , 2021). In young clusters the
stellar density is much higher than in the field, therefore, the ISO capture
rate per Myr is naturally much higher. However, whether the capture
probability is in general higher during the short cluster phase than over the
entire lifetime of a star depends strongly on the assumed cluster properties
and the stellar mass. The latter determines the capture cross section and the
lifetime of a star. Besides, GAIA data strongly indicate that clusters seem
not completely dissolved within 10 Myr, but move together in an unbound state
for a considerable length of time. Thus assuming field densities for the stars
and the ISOs underestimate the capture rates in the first few hundred Myr.
This requires further investigation in the future.

On average every star will contribute ISOs to the galactic population, and
this material might be injected into the inner regions of star systems.
_Seligman et al._ (2022a) suggest that this material can impact both the host
stars and their planets, enriching their atmospheres, and that understanding
the composition of the ISO population will have implications for post-
formation exoplanet atmospheric composition.

Currently there exists no definitive evidence that any gravitationally bound
objects in the solar system are of extrinsic origin (_Morbidelli et al._ ,
2020). However, the discovery of 1I/‘Oumuamua and 2I/Borisov sparked wide-
ranging speculation regarding the possibility that our solar system is being
more broadly contaminated by minor bodies of extra-solar origin (_Siraj and
Loeb_ , 2019; _Namouni and Morais_ , 2020; _Hands and Dehnen_ , 2020). There
exists a wide range in the estimated masses of planetesimals accreted from
other stars while the Sun lived within its birth cluster from
10${}^{-5}{\rm\,M_{\oplus}}$ to a third of the Oort cloud population. _Napier
et al._ (2021) finds that about $10^{6}$ more ISOs were captured during the
cluster phase than accreted subsequently from the field, while the current
steady state factor is $10^{4}$ and the total mass of surviving captured ISOs
is $\sim 10^{-9}{\rm\,M_{\oplus}}$. To put this into perspective, the mass of
the Oort cloud is estimated to range from 0.75 $\pm$ 0.25 ${\rm\,M_{\oplus}}$
(_Brasser_ , 2008) to 1.9 ${\rm\,M_{\oplus}}$ (_Weissman_ , 1996). With a
typical comet-mass of a few times 1012 to 1014 kg (_Sosa and Fernández_ ,
2011) the Oort cloud contains approximately 1010-1012 comet-sized objects.
Thus the captured ISO population is probably extremely small in comparison to
the primordial comet population in the Oort cloud.

Current capture of ISOs into the solar system has also been explored. _Dehnen
et al._ (2022) suggest that planets capture $\sim$2 ISOs every 1000 years
which would result in 8 ISOs captured within 5 au of the Sun at any time. A
perennial candidate for a captured ISO is comet 96P/Machholz, due to its
highly anomalous optical spectrum that is dominated by NH2, with strong
depletions of carbon-based molecules (_Langland-Shula and Smith_ , 2007;
_Schleicher_ , 2008). Its orbital elements of $q=0.124$, $i=58^{\circ}$ and
$e=0.959$ mark it as one of the lowest perihelia comets known, although its
high inclination is due to strong Kozai-Lidov oscillations (_McIntosh_ ,
1990). Its nucleus was studied by _Eisner et al._ (2019) to compare with
1I/‘Oumuamua to search for possible effects of small perihelion passages. The
strongest evidence for it being a captured ISO remains its peculiar coma
composition, but this is not a definitive marker.

####  7.2.3 Intergalactic Objects

The existence of ISOs in the Milky Way makes it likely that other galaxies are
also populated with large numbers of ISOs. One can also speculate about the
number of objects that have been ejected from their parent galaxy and become
Intergalactic Objects. These would clearly be difficult to create, given the
huge velocities required; at the Sun’s position the escape velocity from the
Milky Way is $\simeq 500$ km/s (_Koppelman and Helmi_ , 2021). While some tens
of hypervelocity stars escaping the Milky Way have now been identified (_Li et
al._ , 2021), most are thought to have attained their velocities via
encounters with massive black holes, whose dynamical and radiation
environments are hardly conducive for ISO survival.

However, we note that while escape to intergalactic space is highly unlikely
for an ISO, we can let the galaxy carry it to a new home. Galactic mergers
have taken place throughout the history of the Universe, with 5 minor mergers
identified for the Milky Way (_Kruijssen et al._ , 2020). An unknown fraction
of the ISOs in those galaxies would have merged with the galactic population,
and of course subsumed stellar systems would have ejected their own ISOs
through the usual methods described in §4. Hence given enough time as ISO
detections increase, there is a finite but as-yet unquantified probability of
detecting an ISO carried here by its own galaxy.

###  7.3 The range of ISO properties

####  7.3.1 Future detections and surveys

The trajectory of 1I/‘Oumuamua brought it in from above the plane of the solar
system from the direction of the constellation Lyra (Fig. 11). It came to
perihelion inside the orbit of Mercury at $q$ = 0.255 au on 2017 Sep. 9. and
was discovered post-perihelion at $r$ = 1.22 au after it had made its close
approach to Earth on 2017 Oct. 14. This close approach was at 0.162 au,
passing within 63 lunar distances. Images from the Catalina Sky Survey
detected it on Oct. 14, but it was noted only after it had been discovered.

Figure 11: Path of 1I/‘Oumuamua as it entered the solar system illustrating
why it was not discovered sooner.

1I/‘Oumuamua passed through the SOHO and STEREO fields of view in early 2017
Sep., near perihelion (_Hui and Knight_ , 2019). Because of the large phase
angle and the extreme forward scattering, this would have enhanced the
brightness of any dust around the nucleus by $\sim$ two orders of magnitude
but neither satellite detected it. It could not have been discovered any
earlier than it was because 1I/‘Oumuamua was just coming out of solar
conjunction as seen from the ground and was faint (mag$\sim$23.7 at 0.79 au on
Oct. 2). Prior to moving into solar conjunction in early August it would have
been fainter than mag$\sim$25 - both times too faint to be discovered by any
of the existing surveys. 1I/‘Oumuamua was inside the orbit of Jupiter for less
than 1.3 yrs. The second ISO was discovered by an amateur searching close to
the horizon in twilight – something that the large telescope surveys cannot do
(see Bauer et al., this volume).

The Rubin observatory in Chile has an 8.3m survey telescope with a camera that
covers a FOV of 9.6 deg2. It will begin regular survey operations in mid-2025
that will provide a much greater depth than all previous surveys, reaching
mag$\sim$24.7 and scanning the accessible sky every 3 days (_Jones et al._ ,
2009). _Hoover et al._ (2022) have estimated the number of discoveries that
might be made by the LSST by generating a synthetic population of ISOs,
assuming no cometary activity. They predict that the survey will find on the
order of 1 ISO per year, but the number can be larger than 1 when cometary
activity is considered. Ironically, however, even had the LSST survey been
operational in 2017, it would have been unlikely to discover 1I/‘Oumuamua
because the ISO would have had an average brightness brighter than
mag$\sim$24.7 for less than a week before moving into solar conjunction in
early 2017 Aug.

####  7.3.2 Probing origins and evolution

The standard mechanisms of ISO creation via ejection of exocomets from their
home systems are described in detail in §4. 1I/‘Oumuamua’s discovery resulted
in the proposal of additional possible creation routes. Many of the formation
mechanisms have been suggested in an attempt to explain the origin of the
unusual shape for 1I/‘Oumuamua. These include fluidization to a Jacobi
ellipsoid during the red giant phase of a star (_Katz_ , 2018), interstellar
ablation (_Vavilov and Medvedev_ , 2019), collisional elongation (_Sugiura et
al._ , 2019), formation as an icy fractal aggregate (_Moro-Martín_ , 2019a)
and a tidally disrupted planetesimal that passed close to growing giant
planets, from which the volatiles were removed during a close stellar passage
(_Raymond et al._ , 2018a; _Zhang and Lin_ , 2020).

Two 1I/‘Oumuamua origin scenarios suggested a volatile composition based on
homonuclear diatomic molecules with no dipole moments and no vibrational
spectral lines, which would explain why no gas was detected. In an attempt to
both explain the shape and acceleration of 1I/‘Oumuamua, _Seligman and
Laughlin_ (2020) suggested that it was composed of molecular hydrogen ice. In
their model, mass wasting from sublimation far out in the solar system could
explain both the shape and the acceleration. They proposed that the ISO formed
in a cold dense molecular cloud core. The freezing point of H2 is around 14K,
and the lowest temperature cloud cores are around 10K. H2 has no dipole moment
and can only be detected in the far-UV or in the infrared through its
rotational lines from space. An alternate suggestion was made by _Desch and
Jackson_ (2021) who proposed that 1I/‘Oumuamua was a collisional fragment from
an exo-Kuiper belt. Many large KBOs in our solar system exhibit N2 ice on
their surfaces. Gaseous N2 has no bending mode vibration spectral lines and is
infra-red inactive. Its spectral features are in the UV where no observations
were taken. This makes it an attractive volatile to explain how 1I/‘Oumuamua
could have unobserved outgassing. _Levine et al._ (2021) suggests that neither
scenario is plausible because large H2-ice bodies are not likely to form in
cloud cores and that the impacts in a Kuiper belt are not sufficient to
generate large N2 fragments.

Figure 12: Genetic relationships of early solar system planetesimals both in
our solar system and from exoplanetary systems. We are just at the beginning
of exploring the ISO population. Objects on OCC orbits, including ISOs,
represent the largest reservoir of objects that has not been explored with an
in-situ mission. HTC = Halley Type comet, JFC = Jupiter Family Comet).

In order to reconcile some of the observational and model inconsistencies,
_Bergner and Seligman_ (2023) propose that the acceleration of 1I/‘Oumuamua is
caused by release of molecular hydrogen that formed by cosmic ray processing
of water ice. These authors argue that laboratory experiments show that H2 is
efficiently produced in water ice during radiation by high energy particles.
They propose that the H2 gas is released over a wide range of temperatures
during annealing of amorphous water ice and that there is sufficient gas
released to account for the observed non-gravitational acceleration.

Finally, regarding origin location within a disk, _Seligman et al._ (2022b)
propose that measuring the C/O ratio of an ISO can be a tracer of whether the
ISO formed inside or outside the ice line in its home star system.

###  7.4 In-situ Observations: Space missions

1I‘/Oumuamua was accessible to ground based telescopes for less than a month,
a little longer using space facilities. After this brief period of observation
it was found that the characteristics were quite different from what was
expected from the first ISO, and this one discovery has energized a new
interdisciplinary awareness in the study of planet formation. However, a more
detailed investigation of ISOs with an in-situ mission presents unique
challenges: the orbits may have high inclinations and the encounter speeds are
typically high (10s of km/s) which means a short encounter. There are
increased risks with high velocity flybys if the ISO ejects large dust
particles. The Giotto spacecraft was destabilized with a cm-sized impactor at
a relative velocity of 68 km/s (_Bird et al._ , 1988).

NASA’s competed mission calls are not compatible with missions that are
responsive to new discoveries, i.e., missions that do not have a target at the
time they are proposed. This is relevant for ISOs as well as OCCs, Manx
comets, and hazardous NEOs. Two approaches have been suggested to explore
these targets: spacecraft in storage, ready to launch following target
discovery and spacecraft in a standby orbit, as is being done by ESA’s Comet
Interceptor mission (see Snodgrass et al this volume, and _Snodgrass and
Jones_ , 2019; _Sánchez et al._ , 2021). Typically, the target will be unknown
at the time of spacecraft development and this has an effect on the definition
of basic spacecraft capability (e.g., $\Delta$v) and on the payload. Launch
following the discovery of an ISO offers a greater flexibility in terms of
target access but requires a very fast turnaround of a launch vehicle. A
spacecraft in a standby orbit is more responsive to a target but has a more
limited target accessibility.

Using known OCC orbits, an assessment of the phase space of targets with
available launch energies, maximum encounter speed and for times of flight of
less than 10 years, launching while the comet is more than 0.5 years from
coming to perihelion, shows that for low launch energies, C3, there are almost
no targets. (In astrodynamics, the characteristic energy C3 km2/s2 is the
measure of the excess specific energy over that required to just barely escape
a massive body; C3 = v${}_{\infty}^{2}$.) There are also almost no targets
unless the encounter speeds are greater than 10 km/s. This suggests that at
present only fast flyby missions are an option for ISOs. For a comprehensive
mission, this likely requires significant advancements in payload capabilities
(e.g. small deployable satellites and autonomous navigation) (_Donitz et al._
, 2021, 2022).

There were several concepts developed for missions that could reach
1I/‘Oumuamua. _Seligman and Laughlin_ (2018) estimated that for launch-on-
detection scenarios, the wait time would be on the order of 10 years for a
favorable mission opportunity. _Hibberd et al._ (2020) explored a range of
flyby trajectories which could launch in the early 2030’s and deliver a
spacecraft to 1I/‘Oumuamua with relative velocities between 15-20 km/s,
arriving between 2048-2052. Finally, _Miller et al._ (2022) proposed high-
performance solar sail scenarios that would allow for a rendezvous with an ISO
by maintaining a high potential energy position until the detection of an ISO
and then matching velocity through a controlled fall toward the Sun.

The LSST survey will increase the number of discoveries by going much fainter,
and therefore to larger discovery distances. As shown by _Engelhardt et al._
(2017), ISOs are more common at larger perihelion distances. The fainter
limiting survey magnitude would enable detection of a 1 km inactive nucleus
with 4% albedo out to 5.5 au, active ISOs much further. Although most detected
ISOs may be too distant to easily reach with spacecraft, 1I/‘Oumuamua and
2I/Borisov demonstrate ISOs exist that come within 2 au, and detection of an
incoming ISO at large distances may provide enough warning time for either the
storage or standby concepts discussed above.

##  8 SUMMARY

From the multitude of studies described in this chapter, it is clear that
exocomets should be and are common in nearby stellar systems. Together with
the physical mechanisms by which they can be lost to interstellar space, the
local stellar neighborhood should be rich in ISOs, a prediction finally
confirmed through the discovery of 1I/‘Oumuamua and 2I/Borisov. So the
question remains, how is 1I/‘Oumuamua not visibly active while 2I/Borisov is
strongly active; is this due to origin, age, or the unseen 1I/‘Oumuamua
perihelion passage? From models of our solar system (_Shannon et al._ , 2015),
some fraction of ISOs will not be cometary but more like C- or S-type
asteroids. Based on the observation of Manx comets (_Meech et al._ , 2016), we
should be able to distinguish asteroidal objects from inert comets. Is there a
continuum of properties for ISOs, or have we already found two separate
populations arriving from different origin mechanisms? This sample of two very
different ISOs makes it difficult to predict what will 3I be like - will it be
like planetesimals from our solar system or something different (see Fig. 12)?
Given the increasing sensitivity of sky surveys, the current and next
generation of optical, IR and sub-mm facilities, plus the theoretical advances
in cometary/exocomet structure and evolution, these open questions have a
chance of being answered in Comets IV.

Acknowledgments

We thank the reviewers, Matthew Knight, Sean Raymond and an anonymous referee
for the very thorough and helpful reviews on a very short timescale! K.J.M.
acknowledges support through NASA Grant 80-NSSC18K0853 and in addition to
support for HST programs GO/DD-15405, -15447, 16043, -16088, and -16915
provided by NASA through a grant from the Space Telescope Science Institute,
which is operated by the Association of Universities for Research in Astronomy
under NASA contract NAS 5-26555. A.F. acknowledges support from UK STFC award
ST/X000923/1. Figure 5 is based on data obtained from the ESO Science Archive
Facility with DOI https://doi.org/10.18727/archive/33 .

## References

  * _Abedin et al._ (2022) Abedin A. Y., Kavelaars J. J., Petit J.-M. et al. (2022) _OSSOS. XXVI. On the Lack of Catastrophic Collisions in the Present Kuiper Belt_ , _AJ_ , _164_ , 261.
  * _Adams_ (2010) Adams F. C. (2010) _The Birth Environment of the Solar System_ , _ARA &A_, _48_ , 47–85.
  * _Adams et al._ (2006) Adams F. C., Proszkow E. M., Fatuzzo M. et al. (2006) _Early Evolution of Stellar Groups and Clusters: Environmental Effects on Forming Planetary Systems_ , _ApJ_ , _641_ , 504–525.
  * _Adams and Spergel_ (2005) Adams F. C. and Spergel D. N. (2005) _Lithopanspermia in Star-Forming Clusters_ , _Astrobiology_ , _5_ , 497–514.
  * _Andrews_ (2020) Andrews S. M. (2020) _Observations of Protoplanetary Disk Structures_ , _ARA &A_, _58_ , 483–528.
  * _Andrews et al._ (2018) Andrews S. M., Terrell M., Tripathi A. et al. (2018) _Scaling Relations Associated with Millimeter Continuum Sizes in Protoplanetary Disks_ , _ApJ_ , _865_ , 157.
  * _Ansdell et al._ (2016) Ansdell M., Williams J. P., van der Marel N. et al. (2016) _ALMA Survey of Lupus Protoplanetary Disks. I. Dust and Gas Masses_ , _ApJ_ , _828_ , 46.
  * _Apai et al._ (2015) Apai D., Schneider G., Grady C. A. et al. (2015) _The Inner Disk Structure, Disk-Planet Interactions, and Temporal Evolution in the $\beta$ Pictoris System: A Two-epoch HST/STIS Coronagraphic Study_, _ApJ_ , _800_ , 136.
  * _Aravind et al._ (2021) Aravind K., Ganesh S., Venkataramani K. et al. (2021) _Activity of the first interstellar comet 2I/Borisov around perihelion: results from Indian observatories_ , _MNRAS_ , _502_ , 3491–3499.
  * _Armitage_ (2018) Armitage P. J. (2018) _A Brief Overview of Planet Formation_ , p. 135.
  * _Asphaug and Benz_ (1996) Asphaug E. and Benz W. (1996) _Size, Density, and Structure of Comet Shoemaker-Levy 9 Inferred from the Physics of Tidal Breakup_ , _Icarus_ , _121_ , 225–248.
  * _Augereau and Beust_ (2006) Augereau J. C. and Beust H. (2006) _On the AU Microscopii debris disk. Density profiles, grain properties, and dust dynamics_ , _A &A_, _455_ , 987–999.
  * _Aumann et al._ (1984) Aumann H. H., Gillett F. C., Beichman C. A. et al. (1984) _Discovery of a shell around alpha Lyrae._ , _ApJ_ , _278_ , L23–L27.
  * _Backman and Paresce_ (1993) Backman D. E. and Paresce F. (1993) in _Protostars and Planets III_ (E. H. Levy and J. I. Lunine, eds.), p. 1253.
  * _Baggaley_ (2000) Baggaley W. J. (2000) _Advanced Meteor Orbit Radar observations of interstellar meteoroids_ , _J. Geophys. Res._ , _105_ , 10353–10362.
  * _Bailer-Jones et al._ (2018) Bailer-Jones C. A. L., Farnocchia D., Meech K. J. et al. (2018) _Plausible Home Stars of the Interstellar Object ‘Oumuamua Found in Gaia DR2_ , _AJ_ , _156_ , 205.
  * _Bailer-Jones et al._ (2020) Bailer-Jones C. A. L., Farnocchia D., Ye Q. et al. (2020) _A search for the origin of the interstellar comet 2I/Borisov_ , _A &A_, _634_ , A14.
  * _Bate et al._ (2003) Bate M. R., Bonnell I. A., and Bromm V. (2003) _The formation of a star cluster: predicting the properties of stars and brown dwarfs_ , _MNRAS_ , _339_ , 577–599.
  * _Bauer et al._ (2017) Bauer J. M., Grav T., Fernández Y. R. et al. (2017) _Debiasing the NEOWISE Cryogenic Mission Comet Populations_ , _AJ_ , _154_ , 53\.
  * _Baxter et al._ (2018) Baxter E. J., Blake C. H., and Jain B. (2018) _Probing Oort Clouds around Milky Way Stars with CMB Surveys_ , _AJ_ , _156_ , 243.
  * _Belton et al._ (2018) Belton M. J. S., Hainaut O. R., Meech K. J. et al. (2018) _The Excited Spin State of 1I/2017 U1 ‘Oumuamua_ , _ApJ_ , _856_ , L21.
  * _Bergner and Seligman_ (2023) Bergner J. B. and Seligman D. Z. (2023) _Acceleration of 1I‘/Oumuamua from radiolytically produced H 2 in H2O ice_, _Nature_ , _615_ , xxx–xxx.
  * _Bernstein et al._ (2004) Bernstein G. M., Trilling D. E., Allen R. L. et al. (2004) _The Size Distribution of Trans-Neptunian Bodies_ , _AJ_ , _128_ , 1364–1390.
  * _Beust and Morbidelli_ (2000) Beust H. and Morbidelli A. (2000) _Falling Evaporating Bodies as a Clue to Outline the Structure of the $\beta$ Pictoris Young Planetary System_, _Icarus_ , _143_ , 170–188.
  * _Bird et al._ (1988) Bird M. K., Pätzold M., Volland H. et al. (1988) _Giotto spacecraft dynamics during the encounter with comet Halley._ , _ESA Journal_ , _12_ , 149–169.
  * _Birnstiel and Andrews_ (2014) Birnstiel T. and Andrews S. M. (2014) _On the Outer Edges of Protoplanetary Dust Disks_ , _ApJ_ , _780_ , 153.
  * _Blum and Wurm_ (2008) Blum J. and Wurm G. (2008) _The growth mechanisms of macroscopic bodies in protoplanetary disks._ , _ARA &A_, _46_ , 21–56.
  * _Bodewits et al._ (2020) Bodewits D., Noonan J. W., Feldman P. D. et al. (2020) _The carbon monoxide-rich interstellar comet 2I/Borisov_ , _Nature Astronomy_ , _4_ , 867–871.
  * _Bolin and Lisse_ (2020) Bolin B. T. and Lisse C. M. (2020) _Constraints on the spin-pole orientation, jet morphology, and rotation of interstellar comet 2I/Borisov with deep HST imaging_ , _MNRAS_ , _497_ , 4031–4041.
  * _Bonsor et al._ (2014) Bonsor A., Raymond S. N., Augereau J.-C. et al. (2014) _Planetesimal-driven migration as an explanation for observations of high levels of warm, exozodiacal dust_ , _MNRAS_ , _441_ , 2380–2391.
  * _Booth et al._ (2013) Booth M., Kennedy G., Sibthorpe B. et al. (2013) _Resolved debris discs around A stars in the Herschel DEBRIS survey_ , _MNRAS_ , _428_ , 1263–1280.
  * _Borisov and Shustov_ (2021) Borisov G. V. and Shustov B. M. (2021) _Discovery of the First Interstellar Comet and the Spatial Density of Interstellar Objects in the Solar Neighborhood_ , _Solar System Research_ , _55_ , 124–131.
  * _Borovička et al._ (2022) Borovička J., Spurný P., and Shrbený L. (2022) _Data on 824 fireballs observed by the digital cameras of the European Fireball Network in 2017-2018. II. Analysis of orbital and physical properties of centimeter-sized meteoroids_ , _A &A_, _667_ , A158.
  * _Boss_ (1997) Boss A. P. (1997) _Giant planet formation by gravitational instability._ , _Science_ , _276_ , 1836–1839.
  * _Brandeker et al._ (2004) Brandeker A., Liseau R., Olofsson G. et al. (2004) _The spatial structure of the $\beta$ Pictoris gas disk_, _A &A_, _413_ , 681–691.
  * _Brandl et al._ (2010) Brandl B. R., Lenzen R., Pantin E. et al. (2010) in _Ground-based and Airborne Instrumentation for Astronomy III_ (I. S. McLean, S. K. Ramsay, and H. Takami, eds.), vol. 7735 of _Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series_ , p. 77352G.
  * _Brasser_ (2008) Brasser R. (2008) _A two-stage formation process for the Oort comet cloud and its implications_ , _A &A_, _492_ , 251–255.
  * _Brasser et al._ (2006) Brasser R., Duncan M. J., and Levison H. F. (2006) _Embedded star clusters and the formation of the Oort Cloud_ , _Icarus_ , _184_ , 59–82.
  * _Brown_ (2001) Brown M. E. (2001) _The Inclination Distribution of the Kuiper Belt_ , _AJ_ , _121_ , 2804–2814.
  * _Burns et al._ (1979) Burns J. A., Lamy P. L., and Soter S. (1979) _Radiation forces on small particles in the solar system_ , _Icarus_ , _40_ , 1–48.
  * _Carrera et al._ (2017) Carrera D., Gorti U., Johansen A. et al. (2017) _Planetesimal Formation by the Streaming Instability in a Photoevaporating Disk_ , _ApJ_ , _839_ , 16.
  * _Cataldi et al._ (2018) Cataldi G., Brandeker A., Wu Y. et al. (2018) _ALMA Resolves C I Emission from the $\beta$ Pictoris Debris Disk_, _ApJ_ , _861_ , 72.
  * _Cataldi et al._ (2020) Cataldi G., Wu Y., Brandeker A. et al. (2020) _The Surprisingly Low Carbon Mass in the Debris Disk around HD 32297_ , _ApJ_ , _892_ , 99\.
  * _Chen et al._ (2014) Chen C. H., Mittal T., Kuchner M. et al. (2014) _The Spitzer Infrared Spectrograph Debris Disk Catalog. I. Continuum Analysis of Unresolved Targets_ , _ApJS_ , _211_ , 25.
  * _Chiang et al._ (2009) Chiang E., Kite E., Kalas P. et al. (2009) _Fomalhaut’s Debris Disk and Planet: Constraining the Mass of Fomalhaut b from disk Morphology_ , _ApJ_ , _693_ , 734–749.
  * _Colas et al._ (2020) Colas F., Zanda B., Bouley S. et al. (2020) _FRIPON: a worldwide network to track incoming meteoroids_ , _A &A_, _644_ , A53.
  * _Concha-Ramírez et al._ (2019) Concha-Ramírez F., Wilhelm M. J. C., Portegies Zwart S. et al. (2019) _External photoevaporation of circumstellar discs constrains the time-scale for planet formation_ , _MNRAS_ , _490_ , 5678–5690.
  * _Cordiner et al._ (2020) Cordiner M. A., Milam S. N., Biver N. et al. (2020) _Unusually high CO abundance of the first active interstellar comet_ , _Nature Astronomy_ , _4_ , 861–866.
  * _Ćuk_ (2018) Ćuk M. (2018) _1I/‘Oumuamua as a Tidal Disruption Fragment from a Binary Star System_ , _ApJ_ , _852_ , L15.
  * _Czechowski and Mann_ (2007) Czechowski A. and Mann I. (2007) _Collisional Vaporization of Dust and Production of Gas in the $\beta$ Pictoris Dust Disk_, _ApJ_ , _660_ , 1541–1555.
  * _Daley et al._ (2019) Daley C., Hughes A. M., Carter E. S. et al. (2019) _The Mass of Stirring Bodies in the AU Mic Debris Disk Inferred from Resolved Vertical Structure_ , _ApJ_ , _875_ , 87.
  * _Davies et al._ (2018) Davies R., Alves J., Clénet Y. et al. (2018) in _Ground-based and Airborne Instrumentation for Astronomy VII_ (C. J. Evans, L. Simard, and H. Takami, eds.), vol. 10702 of _Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series_ , p. 107021S.
  * _de León et al._ (2019) de León J., Licandro J., Serra-Ricart M. et al. (2019) _Interstellar Visitors: A Physical Characterization of Comet C/2019 Q4 (Borisov) with OSIRIS at the 10.4 m GTC_ , _Research Notes of the American Astronomical Society_ , _3_ , 131.
  * _Dehnen et al._ (2022) Dehnen W., Hands T. O., and Schönrich R. (2022) _Capture of interstellar objects - II. By the Solar system_ , _MNRAS_ , _512_ , 4078–4085.
  * _Deienno et al._ (2017) Deienno R., Morbidelli A., Gomes R. S. et al. (2017) _Constraining the Giant Planets’ Initial Configuration from Their Evolution: Implications for the Timing of the Planetary Instability_ , _AJ_ , _153_ , 153.
  * _Dent et al._ (2005) Dent W. R. F., Greaves J. S., and Coulson I. M. (2005) _CO emission from discs around isolated HAeBe and Vega-excess stars_ , _MNRAS_ , _359_ , 663–676.
  * _Dent et al._ (2014) Dent W. R. F., Wyatt M. C., Roberge A. et al. (2014) _Molecular Gas Clumps from the Destruction of Icy Bodies in the $\beta$ Pictoris Debris Disk_, _Science_ , _343_ , 1490–1492.
  * _Desch and Jackson_ (2021) Desch S. J. and Jackson A. P. (2021) _1I/‘Oumuamua as an N 2 Ice Fragment of an Exo Pluto Surface II: Generation of N2 Ice Fragments and the Origin of ‘Oumuamua_, _Journal of Geophysical Research (Planets)_ , _126_ , e06807.
  * _Di Ruscio et al._ (2020) Di Ruscio A., Fienga A., Durante D. et al. (2020) _Analysis of Cassini radio tracking data for the construction of INPOP19a: A new estimate of the Kuiper belt mass_ , _A &A_, _640_ , A7.
  * _Do et al._ (2018) Do A., Tucker M. A., and Tonry J. (2018) _Interstellar Interlopers: Number Density and Origin of ‘Oumuamua-like Objects_ , _ApJ_ , _855_ , L10.
  * _Dohnanyi_ (1969) Dohnanyi J. S. (1969) _Collisional Model of Asteroids and Their Debris_ , _J. Geophys. Res._ , _74_ , 2531–2554.
  * _Dominik and Decin_ (2003) Dominik C. and Decin G. (2003) _Age Dependence of the Vega Phenomenon: Theory_ , _ApJ_ , _598_ , 626–635.
  * _Dones et al._ (2015) Dones L., Brasser R., Kaib N. et al. (2015) _Origin and Evolution of the Cometary Reservoirs_ , _Space Sci. Rev._ , _197_ , 191–269.
  * _Donitz et al._ (2021) Donitz B., Meech K. J., Castillo-Rogez J. et al. (2021) in _Bulletin of the American Astronomical Society_ , vol. 53, p. 344.
  * _Donitz et al._ (2022) Donitz B. P. S., Mages D., Tsukamoto H. et al. (2022) _Interstellar Object Accessibility and Mission Design_ , _arXiv e-prints_ , arXiv:2210.14980.
  * _Douglas et al._ (2022) Douglas E. S., Debes J., Mennesson B. et al. (2022) _Sensitivity of the Roman Coronagraph Instrument to Exozodiacal Dust_ , _PASP_ , _134_ , 024402.
  * _Dubrulle et al._ (1995) Dubrulle B., Morfill G., and Sterzik M. (1995) _The dust subdisk in the protoplanetary nebula._ , _Icarus_ , _114_ , 237–246.
  * _Duchêne et al._ (2014) Duchêne G., Arriaga P., Wyatt M. et al. (2014) _Spatially Resolved Imaging of the Two-component $\eta$ Crv Debris Disk with Herschel_, _ApJ_ , _784_ , 148.
  * _Duchêne and Kraus_ (2013) Duchêne G. and Kraus A. (2013) _Stellar Multiplicity_ , _ARA &A_, _51_ , 269–310.
  * _Dullemond and Dominik_ (2004) Dullemond C. P. and Dominik C. (2004) _Flaring vs. self-shadowed disks: The SEDs of Herbig Ae/Be stars_ , _A &A_, _417_ , 159–168.
  * _Duncan et al._ (1987) Duncan M., Quinn T., and Tremaine S. (1987) _The Formation and Extent of the Solar System Comet Cloud_ , _AJ_ , _94_ , 1330.
  * _Dybczyński and Królikowska_ (2018) Dybczyński P. A. and Królikowska M. (2018) _Investigating the dynamical history of the interstellar object ’Oumuamua_ , _A &A_, _610_ , L11.
  * _Eiroa et al._ (2013) Eiroa C., Marshall J. P., Mora A. et al. (2013) _DUst around NEarby Stars. The survey observational results_ , _A &A_, _555_ , A11.
  * _Eisner et al._ (2019) Eisner N. L., Knight M. M., Snodgrass C. et al. (2019) _Properties of the Bare Nucleus of Comet 96P/Machholz 1_ , _AJ_ , _157_ , 186.
  * _Engelhardt et al._ (2017) Engelhardt T., Jedicke R., Vereš P. et al. (2017) _An Observational Upper Limit on the Interstellar Number Density of Asteroids and Comets_ , _AJ_ , _153_ , 133.
  * _Ercolano and Pascucci_ (2017) Ercolano B. and Pascucci I. (2017) _The dispersal of planet-forming discs: theory confronts observations_ , _Royal Society Open Science_ , _4_ , 170114.
  * _Ertel et al._ (2020) Ertel S., Defrère D., Hinz P. et al. (2020) _The HOSTS Survey for Exozodiacal Dust: Observational Results from the Complete Survey_ , _AJ_ , _159_ , 177.
  * _Esposito et al._ (2020) Esposito T. M., Kalas P., Fitzgerald M. P. et al. (2020) _Debris Disk Results from the Gemini Planet Imager Exoplanet Survey’s Polarimetric Imaging Campaign_ , _AJ_ , _160_ , 24.
  * _Eubanks et al._ (2021) Eubanks T. M., Hein A. M., Lingam M. et al. (2021) _Interstellar Objects in the Solar System: 1. Isotropic Kinematics from the Gaia Early Data Release 3_ , _arXiv e-prints_ , arXiv:2103.03289.
  * _Faramaz et al._ (2019) Faramaz V., Krist J., Stapelfeldt K. R. et al. (2019) _From Scattered-light to Millimeter Emission: A Comprehensive View of the Gigayear-old System of HD 202628 and its Eccentric Debris Ring_ , _AJ_ , _158_ , 162.
  * _Faramaz et al._ (2021) Faramaz V., Marino S., Booth M. et al. (2021) _A Detailed Characterization of HR 8799’s Debris Disk with ALMA in Band 7_ , _AJ_ , _161_ , 271.
  * _Farihi_ (2016) Farihi J. (2016) _Circumstellar debris and pollution at white dwarf stars_ , _New A Rev._ , _71_ , 9–34.
  * _Farihi et al._ (2013) Farihi J., Gänsicke B. T., and Koester D. (2013) _Evidence for Water in the Rocky Debris of a Disrupted Extrasolar Minor Planet_ , _Science_ , _342_ , 218–220.
  * _Ferlet et al._ (1987) Ferlet R., Hobbs L. M., and Vidal-Madjar A. (1987) _The beta Pictoris circumstellar disk. V. Time variations of the Ca II-K line._ , _A &A_, _185_ , 267–270.
  * _Fernandez and Ip_ (1984) Fernandez J. A. and Ip W. H. (1984) _Some dynamical aspects of the accretion of Uranus and Neptune: The exchange of orbital angular momentum with planetesimals_ , _Icarus_ , _58_ , 109–120.
  * _Fernández et al._ (2013) Fernández Y. R., Kelley M. S., Lamy P. L. et al. (2013) _Thermal properties, sizes, and size distribution of Jupiter-family cometary nuclei_ , _Icarus_ , _226_ , 1138–1170.
  * _Festou et al._ (2004) Festou M. C., Keller H. U., and Weaver H. A. (2004) _Comets II_.
  * _Fitzsimmons et al._ (2019) Fitzsimmons A., Hainaut O., Meech K. J. et al. (2019) _Detection of CN Gas in Interstellar Object 2I/Borisov_ , _ApJ_ , _885_ , L9.
  * _Fitzsimmons et al._ (2018) Fitzsimmons A., Snodgrass C., Rozitis B. et al. (2018) _Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 ‘Oumuamua_ , _Nature Astronomy_ , _2_ , 133–137.
  * _Flaherty et al._ (2019) Flaherty K., Hughes A. M., Mamajek E. E. et al. (2019) _The Planet Formation Potential around a 45 Myr Old Accreting M Dwarf_ , _ApJ_ , _872_ , 92.
  * _Francis_ (2005) Francis P. J. (2005) _The Demographics of Long-Period Comets_ , _ApJ_ , _635_ , 1348–1361.
  * _Fraser et al._ (2014) Fraser W. C., Brown M. E., Morbidelli A. et al. (2014) _The Absolute Magnitude Distribution of Kuiper Belt Objects_ , _ApJ_ , _782_ , 100.
  * _Friebe et al._ (2022) Friebe M. F., Pearce T. D., and Löhne T. (2022) _Gap carving by a migrating planet embedded in a massive debris disc_ , _MNRAS_ , _512_ , 4441–4454.
  * _Froncisz et al._ (2020) Froncisz M., Brown P., and Weryk R. J. (2020) _Possible interstellar meteoroids detected by the Canadian Meteor Orbit Radar_ , _Planet. Space Sci._ , _190_ , 104980.
  * _Gallart et al._ (2019) Gallart C., Bernard E. J., Brook C. B. et al. (2019) _Uncovering the birth of the Milky Way through accurate stellar ages with Gaia_ , _Nature Astronomy_ , _3_ , 932–939.
  * _Gänsicke et al._ (2012) Gänsicke B. T., Koester D., Farihi J. et al. (2012) _The chemical diversity of exo-terrestrial planetary debris around white dwarfs_ , _MNRAS_ , _424_ , 333–347.
  * _Garufi et al._ (2018) Garufi A., Benisty M., Pinilla P. et al. (2018) _Evolution of protoplanetary disks from their taxonomy in scattered light: spirals, rings, cavities, and shadows_ , _A &A_, _620_ , A94.
  * _Gáspár et al._ (2012) Gáspár A., Psaltis D., Rieke G. H. et al. (2012) _Modeling Collisional Cascades in Debris Disks: Steep Dust-size Distributions_ , _ApJ_ , _754_ , 74.
  * _Geiler et al._ (2019) Geiler F., Krivov A. V., Booth M. et al. (2019) _The scattered disc of HR 8799_ , _MNRAS_ , _483_ , 332–341.
  * _Gladman et al._ (1997) Gladman B. J., Migliorini F., Morbidelli A. et al. (1997) _Dynamical lifetimes of objects injected into asteroid belt resonances_ , _Science_ , _277_ , 197–201.
  * _Gomes et al._ (2005) Gomes R., Levison H. F., Tsiganis K. et al. (2005) _Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets_ , _Nature_ , _435_ , 466–469.
  * _Grady et al._ (1996) Grady C. A., Perez M. R., Talavera A. et al. (1996) _The $\beta$ Pictoris phenomenon among Herbig Ae/Be stars. UV and optical high dispersion spectra._, _A &AS_, _120_ , 157–177.
  * _Grigorieva et al._ (2007) Grigorieva A., Thébault P., Artymowicz P. et al. (2007) _Survival of icy grains in debris discs. The role of photosputtering_ , _A &A_, _475_ , 755–764.
  * _Grishin et al._ (2019) Grishin E., Perets H. B., and Avni Y. (2019) _Planet seeding through gas-assisted capture of interstellar objects_ , _MNRAS_ , _487_ , 3324–3332.
  * _Gronoff et al._ (2020) Gronoff G., Maggiolo R., Cessateur G. et al. (2020) _The Effect of Cosmic Rays on Cometary Nuclei. I. Dose Deposition_ , _ApJ_ , _890_ , 89.
  * _Guzik and Drahus_ (2021) Guzik P. and Drahus M. (2021) _Gaseous atomic nickel in the coma of interstellar comet 2I/Borisov_ , _Nature_ , _593_ , 375–378.
  * _Guzik et al._ (2020) Guzik P., Drahus M., Rusek K. et al. (2020) _Initial characterization of interstellar comet 2I/Borisov_ , _Nature Astronomy_ , _4_ , 53–57.
  * _Haisch et al._ (2001) Haisch Karl E. J., Lada E. A., and Lada C. J. (2001) _Disk Frequencies and Lifetimes in Young Clusters_ , _ApJ_ , _553_ , L153–L156.
  * _Hajdukova et al._ (2020) Hajdukova M., Sterken V., Wiegert P. et al. (2020) _The challenge of identifying interstellar meteors_ , _Planet. Space Sci._ , _192_ , 105060.
  * _Hallatt and Wiegert_ (2020) Hallatt T. and Wiegert P. (2020) _The Dynamics of Interstellar Asteroids and Comets within the Galaxy: An Assessment of Local Candidate Source Regions for 1I/’Oumuamua and 2I/Borisov_ , _AJ_ , _159_ , 147\.
  * _Han et al._ (2023) Han Y., Wyatt M. C., and Dent W. R. F. (2023) _Has the dust clump in the debris disc of Beta Pictoris moved?_ , _MNRAS_ , _519_ , 3257–3270.
  * _Hands and Dehnen_ (2020) Hands T. O. and Dehnen W. (2020) _Capture of interstellar objects: a source of long-period comets_ , _MNRAS_ , _493_ , L59–L64.
  * _Hands et al._ (2019) Hands T. O., Dehnen W., Gration A. et al. (2019) _The fate of planetesimal discs in young open clusters: implications for 1I/’Oumuamua, the Kuiper belt, the Oort cloud, and more_ , _MNRAS_ , _490_ , 21–36.
  * _Hanse et al._ (2018) Hanse J., Jílková L., Portegies Zwart S. F. et al. (2018) _Capture of exocomets and the erosion of the Oort cloud due to stellar encounters in the Galaxy_ , _MNRAS_ , _473_ , 5432–5445.
  * _Hazumi et al._ (2020) Hazumi M., Ade P. A. R., Adler A. et al. (2020) in _Space Telescopes and Instrumentation 2020: Optical, Infrared, and Millimeter Wave_ (M. Lystrup and M. D. Perrin, eds.), vol. 11443 of _Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series_ , p. 114432F.
  * _Heinze et al._ (2021) Heinze A. N., Denneau L., Tonry J. L. et al. (2021) _NEO Population, Velocity Bias, and Impact Risk from an ATLAS Analysis_ , _The Planetary Science Journal_ , _2_ , 12.
  * _Hibberd et al._ (2020) Hibberd A., Hein A. M., and Eubanks T. M. (2020) _Project Lyra: Catching 1I/’Oumuamua - Mission opportunities after 2024_ , _Acta Astronautica_ , _170_ , 136–144.
  * _Hoang and Loeb_ (2020) Hoang T. and Loeb A. (2020) _Destruction of Molecular Hydrogen Ice and Implications for 1I/2017 U1 (’Oumuamua)_ , _ApJ_ , _899_ , L23.
  * _Holland et al._ (2017) Holland W. S., Matthews B. C., Kennedy G. M. et al. (2017) _SONS: The JCMT legacy survey of debris discs in the submillimetre_ , _MNRAS_ , _470_ , 3606–3663.
  * _Hoover et al._ (2022) Hoover D. J., Seligman D. Z., and Payne M. J. (2022) _The Population of Interstellar Objects Detectable with the LSST and Accessible for In Situ Rendezvous with Various Mission Designs_ , __,_3_ , 71\.
  * _Hui and Knight_ (2019) Hui M.-T. and Knight M. M. (2019) _New Insights into Interstellar Object 1I/2017 U1 (‘Oumuamua) from SOHO/STEREO Nondetections_ , _AJ_ , _158_ , 256.
  * _Hui et al._ (2020) Hui M.-T., Ye Q.-Z., Föhring D. et al. (2020) _Physical Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)_ , _AJ_ , _160_ , 92.
  * _Hutsemékers et al._ (2021) Hutsemékers D., Manfroid J., Jehin E. et al. (2021) _FeI and NiI in cometary atmospheres. Connections between the NiI/FeI abundance ratio and chemical characteristics of Jupiter-family and Oort-cloud comets_ , _A &A_, _652_ , L1.
  * _Iglesias et al._ (2018) Iglesias D., Bayo A., Olofsson J. et al. (2018) _Debris discs with multiple absorption features in metallic lines: circumstellar or interstellar origin?_ , _MNRAS_ , _480_ , 488–520.
  * _Jackson et al._ (2018) Jackson A. P., Tamayo D., Hammond N. et al. (2018) _Ejection of rocky and icy material from binary star systems: implications for the origin and composition of 1I/‘Oumuamua_ , _MNRAS_ , _478_ , L49–L53.
  * _Jackson et al._ (2014) Jackson A. P., Wyatt M. C., Bonsor A. et al. (2014) _Debris froms giant impacts between planetary embryos at large orbital radii_ , _MNRAS_ , _440_ , 3757–3777.
  * _Jeffers et al._ (2001) Jeffers S. V., Manley S. P., Bailey M. E. et al. (2001) _Near-Earth object velocity distributions and consequences for the Chicxulub impactor_ , _MNRAS_ , _327_ , 126–132.
  * _Jessberger et al._ (2001) Jessberger E. K., Stephan T., Rost D. et al. (2001) in _Interplanetary Dust_ , p. 253.
  * _Jewitt et al._ (2008) Jewitt D., Garland C. A., and Aussel H. (2008) _Deep Search for Carbon Monoxide in Cometary Precursors Using Millimeter Wave Spectroscopy_ , _AJ_ , _135_ , 400–407.
  * _Jewitt et al._ (2020a) Jewitt D., Hui M.-T., Kim Y. et al. (2020a) _The Nucleus of Interstellar Comet 2I/Borisov_ , _ApJ_ , _888_ , L23.
  * _Jewitt et al._ (2020b) Jewitt D., Kim Y., Mutchler M. et al. (2020b) _Outburst and Splitting of Interstellar Comet 2I/Borisov_ , _ApJ_ , _896_ , L39.
  * _Jewitt and Luu_ (2019) Jewitt D. and Luu J. (2019) _Initial Characterization of Interstellar Comet 2I/2019 Q4 (Borisov)_ , _ApJ_ , _886_ , L29.
  * _Jewitt et al._ (2017) Jewitt D., Luu J., Rajagopal J. et al. (2017) _Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes_ , _ApJ_ , _850_ , L36.
  * _Jewitt and Seligman_ (2022) Jewitt D. and Seligman D. Z. (2022) _The Interstellar Interlopers_ , _arXiv e-prints_ , arXiv:2209.08182.
  * _Jones et al._ (2018) Jones G. H., Knight M. M., Battams K. et al. (2018) _The Science of Sungrazers, Sunskirters, and Other Near-Sun Comets_ , _Space Sci. Rev._ , _214_ , 20.
  * _Jones et al._ (2009) Jones R. L., Chesley S. R., Connolly A. J. et al. (2009) _Solar System Science with LSST_ , _Earth Moon and Planets_ , _105_ , 101–105.
  * _Kalas et al._ (2005) Kalas P., Graham J. R., and Clampin M. (2005) _A planetary system as the origin of structure in Fomalhaut’s dust belt_ , _Nature_ , _435_ , 1067–1070.
  * _Katz_ (2018) Katz J. I. (2018) _Why is interstellar object 1I/2017 U1 (‘Oumuamua) rocky, tumbling and possibly very prolate?_ , _MNRAS_ , _478_ , L95–L98.
  * _Kennedy_ (2018) Kennedy G. M. (2018) _Exocomet orbit fitting: accelerating coma absorption during transits of $\beta$ Pictoris_, _MNRAS_ , _479_ , 1997–2006.
  * _Kennedy_ (2020) Kennedy G. M. (2020) _The unexpected narrowness of eccentric debris rings: a sign of eccentricity during the protoplanetary disc phase_ , _Royal Society Open Science_ , _7_ , 200063.
  * _Kennedy et al._ (2019) Kennedy G. M., Hope G., Hodgkin S. T. et al. (2019) _An automated search for transiting exocomets_ , _MNRAS_ , _482_ , 5587–5596.
  * _Kenyon and Bromley_ (2017) Kenyon S. J. and Bromley B. C. (2017) _Variations on Debris Disks. IV. An Improved Analytical Model for Collisional Cascades_ , _ApJ_ , _839_ , 38.
  * _Kiefer et al._ (2014) Kiefer F., Lecavelier des Etangs A., Boissier J. et al. (2014) _Two families of exocomets in the $\beta$ Pictoris system_, _Nature_ , _514_ , 462–464.
  * _Kim et al._ (2020) Kim Y., Jewitt D., Mutchler M. et al. (2020) _Coma Anisotropy and the Rotation Pole of Interstellar Comet 2I/Borisov_ , _ApJ_ , _895_ , L34.
  * _Kimura et al._ (2019) Kimura K., Aton K., Baybayan K. et al. (2019) in _Bulletin of the American Astronomical Society_ , vol. 51, p. 135.
  * _Klessen and Glover_ (2016) Klessen R. S. and Glover S. C. O. (2016) _Physical Processes in the Interstellar Medium_ , _Saas-Fee Advanced Course_ , _43_ , 85.
  * _Klusmeyer et al._ (2021) Klusmeyer J., Hughes A. M., Matrà L. et al. (2021) _A Deep Search for Five Molecules in the 49 Ceti Debris Disk_ , _ApJ_ , _921_ , 56.
  * _Koppelman and Helmi_ (2021) Koppelman H. H. and Helmi A. (2021) _Determination of the escape velocity of the Milky Way using a halo sample selected based on proper motion_ , _A &A_, _649_ , A136.
  * _Kóspál et al._ (2013) Kóspál Á., Moór A., Juhász A. et al. (2013) _ALMA Observations of the Molecular Gas in the Debris Disk of the 30 Myr Old Star HD 21997_ , _ApJ_ , _776_ , 77.
  * _Kral et al._ (2018) Kral Q., Clarke C., and Wyatt M. C. (2018) in _Handbook of Exoplanets_ (H. J. Deeg and J. A. Belmonte, eds.), p. 165.
  * _Kral et al._ (2019) Kral Q., Marino S., Wyatt M. C. et al. (2019) _Imaging [CI] around HD 131835: reinterpreting young debris discs with protoplanetary disc levels of CO gas as shielded secondary discs_ , _MNRAS_ , _489_ , 3670–3691.
  * _Kral et al._ (2021) Kral Q., Pringle J. E., Guilbert-Lepoutre A. et al. (2021) _A molecular wind blows out of the Kuiper belt_ , _A &A_, _653_ , L11.
  * _Kral et al._ (2016) Kral Q., Wyatt M., Carswell R. F. et al. (2016) _A self-consistent model for the evolution of the gas produced in the debris disc of $\beta$ Pictoris_, _MNRAS_ , _461_ , 845–858.
  * _Krijt et al._ (2020) Krijt S., Bosman A. D., Zhang K. et al. (2020) _CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing_ , _ApJ_ , _899_ , 134.
  * _Krist et al._ (2012) Krist J. E., Stapelfeldt K. R., Bryden G. et al. (2012) _Hubble Space Telescope Observations of the HD 202628 Debris Disk_ , _AJ_ , _144_ , 45.
  * _Królikowska and Dybczyński_ (2010) Królikowska M. and Dybczyński P. A. (2010) _Where do long-period comets come from? 26 comets from the non-gravitational Oort spike_ , _MNRAS_ , _404_ , 1886–1902.
  * _Kruijssen et al._ (2020) Kruijssen J. M. D., Pfeffer J. L., Chevance M. et al. (2020) _Kraken reveals itself - the merger history of the Milky Way reconstructed with the E-MOSAICS simulations_ , _MNRAS_ , _498_ , 2472–2491.
  * _Lada and Lada_ (2003) Lada C. J. and Lada E. A. (2003) _Embedded Clusters in Molecular Clouds_ , _ARA &A_, _41_ , 57–115.
  * _Lagrange et al._ (2009) Lagrange A. M., Gratadour D., Chauvin G. et al. (2009) _A probable giant planet imaged in the $\beta$ Pictoris disk. VLT/NaCo deep L’-band imaging_, _A &A_, _493_ , L21–L25.
  * _Lagrange et al._ (2019) Lagrange A. M., Meunier N., Rubini P. et al. (2019) _Evidence for an additional planet in the $\beta$ Pictoris system_, _Nature Astronomy_ , _3_ , 1135–1142.
  * _Lagrange-Henri et al._ (1988) Lagrange-Henri A. M., Vidal-Madjar A., and Ferlet R. (1988) _The beta Pictoris circumstellar disk. VI. Evidence for material falling on to the star._ , _A &A_, _190_ , 275–282.
  * _Lambrechts and Johansen_ (2012) Lambrechts M. and Johansen A. (2012) _Rapid growth of gas-giant cores by pebble accretion_ , _A &A_, _544_ , A32.
  * _Langland-Shula and Smith_ (2007) Langland-Shula L. E. and Smith G. H. (2007) _The Unusual Spectrum of Comet 96P/Machholz_ , _ApJ_ , _664_ , L119–L122.
  * _Läuter et al._ (2020) Läuter M., Kramer T., Rubin M. et al. (2020) _The gas production of 14 species from comet 67P/Churyumov-Gerasimenko based on DFMS/COPS data from 2014 to 2016_ , _MNRAS_ , _498_ , 3995–4004.
  * _Lecavelier des Etangs et al._ (2022) Lecavelier des Etangs A., Cros L., Hébrard G. et al. (2022) _Exocomets size distribution in the $\beta$ ? Pictoris planetary system_, _Scientific Reports_ , _12_ , 5855.
  * _Lecavelier des Etangs et al._ (1999) Lecavelier des Etangs A., Vidal-Madjar A., and Ferlet R. (1999) _Photometric stellar variation due to extra-solar comets_ , _A &A_, _343_ , 916–922.
  * _Lee and Chiang_ (2016) Lee E. J. and Chiang E. (2016) _A Primer on Unifying Debris Disk Morphologies_ , _ApJ_ , _827_ , 125.
  * _Levine et al._ (2021) Levine W. G., Cabot S. H. C., Seligman D. et al. (2021) _Constraints on the Occurrence of ’Oumuamua-Like Objects_ , _ApJ_ , _922_ , 39.
  * _Levison and Duncan_ (1997) Levison H. F. and Duncan M. J. (1997) _From the Kuiper Belt to Jupiter-Family Comets: The Spatial Distribution of Ecliptic Comets_ , _Icarus_ , _127_ , 13–32.
  * _Li et al._ (2021) Li Y.-B., Luo A. L., Lu Y.-J. et al. (2021) _591 High-velocity Stars in the Galactic Halo Selected from LAMOST DR7 and Gaia DR2_ , _ApJS_ , _252_ , 3.
  * _Lin et al._ (2020) Lin H. W., Lee C.-H., Gerdes D. W. et al. (2020) _Detection of Diatomic Carbon in 2I/Borisov_ , _ApJ_ , _889_ , L30.
  * _Lisse et al._ (2012) Lisse C. M., Wyatt M. C., Chen C. H. et al. (2012) _Spitzer Evidence for a Late-heavy Bombardment and the Formation of Ureilites in $\eta$ Corvi at ~1 Gyr_, _ApJ_ , _747_ , 93.
  * _Lisse et al._ (2021) Lisse C. M., Young L. A., Cruikshank D. P. et al. (2021) _On the origin & thermal stability of Arrokoth’s and Pluto’s ices_, _Icarus_ , _356_ , 114072.
  * _Liu et al._ (2022) Liu B., Johansen A., Lambrechts M. et al. (2022) _Natural separation of two primordial planetary reservoirs in an expanding solar protoplanetary disk_ , _Science Advances_ , _8_ , eabm3045.
  * _Löhne_ (2020) Löhne T. (2020) _Relating grain size distributions in circumstellar discs to the spectral index at millimetre wavelengths_ , _A &A_, _641_ , A75.
  * _Löhne et al._ (2008) Löhne T., Krivov A. V., and Rodmann J. (2008) _Long-Term Collisional Evolution of Debris Disks_ , _ApJ_ , _673_ , 1123–1137.
  * _Lombaert et al._ (2016) Lombaert R., Decin L., Royer P. et al. (2016) _Constraints on the H 2O formation mechanism in the wind of carbon-rich AGB stars_, _A &A_, _588_ , A124.
  * _Lovell et al._ (2021) Lovell J. B., Wyatt M. C., Ansdell M. et al. (2021) _ALMA survey of Lupus class III stars: Early planetesimal belt formation and rapid disc dispersal_ , _MNRAS_ , _500_ , 4878–4900.
  * _Luppe et al._ (2020) Luppe P., Krivov A. V., Booth M. et al. (2020) _Observability of dusty debris discs around M-stars_ , _MNRAS_ , _499_ , 3932–3942.
  * _Lynch and Lovell_ (2022) Lynch E. M. and Lovell J. B. (2022) _Eccentric debris disc morphologies - I. Exploring the origin of apocentre and pericentre glows in face-on debris discs_ , _MNRAS_ , _510_ , 2538–2551.
  * _MacGregor et al._ (2022) MacGregor M. A., Hurt S. A., Stark C. C. et al. (2022) _ALMA Images the Eccentric HD 53143 Debris Disk_ , _ApJ_ , _933_ , L1.
  * _MacGregor et al._ (2017) MacGregor M. A., Matrà L., Kalas P. et al. (2017) _A Complete ALMA Map of the Fomalhaut Debris Disk_ , _ApJ_ , _842_ , 8.
  * _Maiolino et al._ (2013) Maiolino R., Haehnelt M., Murphy M. T. et al. (2013) _A Community Science Case for E-ELT HIRES_ , _arXiv e-prints_ , arXiv:1310.3163.
  * _Malamud and Perets_ (2016) Malamud U. and Perets H. B. (2016) _Post-main Sequence Evolution of Icy Minor Planets: Implications for Water Retention and White Dwarf Pollution_ , _ApJ_ , _832_ , 160.
  * _Malhotra_ (1993) Malhotra R. (1993) _The origin of Pluto’s peculiar orbit_ , _Nature_ , _365_ , 819–821.
  * _Mamajek_ (2009) Mamajek E. E. (2009) in _Exoplanets and Disks: Their Formation and Diversity_ (T. Usuda, M. Tamura, and M. Ishii, eds.), vol. 1158 of _American Institute of Physics Conference Series_ , pp. 3–10.
  * _Manara et al._ (2018) Manara C. F., Morbidelli A., and Guillot T. (2018) _Why do protoplanetary disks appear not massive enough to form the known exoplanet population?_ , _A &A_, _618_ , L3.
  * _Manzini et al._ (2020) Manzini F., Oldani V., Ochner P. et al. (2020) _Interstellar comet 2I/Borisov exhibits a structure similar to native Solar system comets_ , _MNRAS_ , _495_ , L92–L96.
  * _Marboeuf et al._ (2016) Marboeuf U., Bonsor A., and Augereau J. C. (2016) _Extrasolar comets: The origin of dust in exozodiacal disks?_ , _Planet. Space Sci._ , _133_ , 47–62.
  * _Marino_ (2021) Marino S. (2021) _Constraining planetesimal stirring: how sharp are debris disc edges?_ , _MNRAS_ , _503_ , 5100–5114.
  * _Marino_ (2022) Marino S. (2022) _Planetesimal/Debris discs_ , _arXiv e-prints_ , arXiv:2202.03053.
  * _Marino et al._ (2018a) Marino S., Bonsor A., Wyatt M. C. et al. (2018a) _Scattering of exocomets by a planet chain: exozodi levels and the delivery of cometary material to inner planets_ , _MNRAS_ , _479_ , 1651–1671.
  * _Marino et al._ (2018b) Marino S., Carpenter J., Wyatt M. C. et al. (2018b) _A gap in the planetesimal disc around HD 107146 and asymmetric warm dust emission revealed by ALMA_ , _MNRAS_ , _479_ , 5423–5439.
  * _Marino et al._ (2020) Marino S., Flock M., Henning T. et al. (2020) _Population synthesis of exocometary gas around A stars_ , _MNRAS_ , _492_ , 4409–4429.
  * _Marino et al._ (2016) Marino S., Matrà L., Stark C. et al. (2016) _Exocometary gas in the HD 181327 debris ring_ , _MNRAS_ , _460_ , 2933–2944.
  * _Marino et al._ (2017) Marino S., Wyatt M. C., Panić O. et al. (2017) _ALMA observations of the $\eta$ Corvi debris disc: inward scattering of CO-rich exocomets by a chain of 3-30 M⊕ planets?_, _MNRAS_ , _465_ , 2595–2615.
  * _Marshall et al._ (2014) Marshall J. P., Moro-Martín A., Eiroa C. et al. (2014) _Correlations between the stellar, planetary, and debris components of exoplanet systems observed by Herschel_ , _A &A_, _565_ , A15.
  * _Marshall et al._ (2021) Marshall J. P., Wang L., Kennedy G. M. et al. (2021) _A search for trends in spatially resolved debris discs at far-infrared wavelengths_ , _MNRAS_ , _501_ , 6168–6180.
  * _Mashchenko_ (2019) Mashchenko S. (2019) _Modelling the light curve of ‘Oumuamua: evidence for torque and disc-like shape_ , _MNRAS_ , _489_ , 3003–3021.
  * _Matrà et al._ (2020) Matrà L., Dent W. R. F., Wilner D. J. et al. (2020) _Dust Populations in the Iconic Vega Planetary System Resolved by ALMA_ , _ApJ_ , _898_ , 146.
  * _Matrà et al._ (2017a) Matrà L., Dent W. R. F., Wyatt M. C. et al. (2017a) _Exocometary gas structure, origin and physical properties around $\beta$ Pictoris through ALMA CO multitransition observations_, _MNRAS_ , _464_ , 1415–1433.
  * _Matrà et al._ (2017b) Matrà L., MacGregor M. A., Kalas P. et al. (2017b) _Detection of Exocometary CO within the 440 Myr Old Fomalhaut Belt: A Similar CO+CO 2 Ice Abundance in Exocomets and Solar System Comets_, _ApJ_ , _842_ , 9.
  * _Matrà et al._ (2018a) Matrà L., Marino S., Kennedy G. M. et al. (2018a) _An Empirical Planetesimal Belt Radius-Stellar Luminosity Relation_ , _ApJ_ , _859_ , 72.
  * _Matrà et al._ (2019a) Matrà L., Öberg K. I., Wilner D. J. et al. (2019a) _On the Ubiquity and Stellar Luminosity Dependence of Exocometary CO Gas: Detection around M Dwarf TWA 7_ , _AJ_ , _157_ , 117.
  * _Matrà et al._ (2015) Matrà L., Panić O., Wyatt M. C. et al. (2015) _CO mass upper limits in the Fomalhaut ring - the importance of NLTE excitation in debris discs and future prospects with ALMA_ , _MNRAS_ , _447_ , 3936–3947.
  * _Matrà et al._ (2018b) Matrà L., Wilner D. J., Öberg K. I. et al. (2018b) _Molecular Reconnaissance of the $\beta$ Pictoris Gas Disk with the SMA: A Low HCN/(CO+CO2) Outgassing Ratio and Predictions for Future Surveys_, _ApJ_ , _853_ , 147.
  * _Matrà et al._ (2019b) Matrà L., Wyatt M. C., Wilner D. J. et al. (2019b) _Kuiper Belt-like Hot and Cold Populations of Planetesimal Inclinations in the $\beta$ Pictoris Belt Revealed by ALMA_, _AJ_ , _157_ , 135.
  * _McCrea_ (1975) McCrea W. H. (1975) _Solar System as space probe_ , _The Observatory_ , _95_ , 239–255.
  * _McIntosh_ (1990) McIntosh B. A. (1990) _Comet P/Machholz and the quadrantid meteor stream_ , _Icarus_ , _86_ , 299–304.
  * _McKay et al._ (2020) McKay A. J., Cochran A. L., Dello Russo N. et al. (2020) _Detection of a Water Tracer in Interstellar Comet 2I/Borisov_ , _ApJ_ , _889_ , L10.
  * _McKay et al._ (2019) McKay A. J., DiSanti M. A., Kelley M. S. P. et al. (2019) _The Peculiar Volatile Composition of CO-dominated Comet C/2016 R2 (PanSTARRS)_ , _AJ_ , _158_ , 128.
  * _McNeill et al._ (2018) McNeill A., Trilling D. E., and Mommert M. (2018) _Constraints on the Density and Internal Strength of 1I/’Oumuamua_ , _ApJ_ , _857_ , L1.
  * _Meech et al._ (2004) Meech K. J., Hainaut O. R., and Marsden B. G. (2004) _Comet nucleus size distributions from HST and Keck telescopes_ , _Icarus_ , _170_ , 463–491.
  * _Meech et al._ (2017a) Meech K. J., Kleyna J. T., Hainaut O. et al. (2017a) _CO-driven Activity in Comet C/2017 K2 (PANSTARRS)_ , _ApJ_ , _849_ , L8.
  * _Meech et al._ (2017b) Meech K. J., Weryk R., Micheli M. et al. (2017b) _A brief visit from a red and extremely elongated interstellar asteroid_ , _Nature_ , _552_ , 378–381.
  * _Meech et al._ (2016) Meech K. J., Yang B., Kleyna J. et al. (2016) _Inner solar system material discovered in the Oort cloud_ , _Science Advances_ , _2_ , e1600038.
  * _Melnick et al._ (2001) Melnick G. J., Neufeld D. A., Ford K. E. S. et al. (2001) _Discovery of water vapour around IRC+10216 as evidence for comets orbiting another star_ , _Nature_ , _412_ , 160–163.
  * _Melosh_ (2003) Melosh H. J. (2003) _Exchange of Meteorites (and Life?) Between Stellar Systems_ , _Astrobiology_ , _3_ , 207–215.
  * _Mesa et al._ (2019) Mesa D., Keppler M., Cantalloube F. et al. (2019) _VLT/SPHERE exploration of the young multiplanetary system PDS70_ , _A &A_, _632_ , A25.
  * _Meshkat et al._ (2017) Meshkat T., Mawet D., Bryan M. L. et al. (2017) _A Direct Imaging Survey of Spitzer-detected Debris Disks: Occurrence of Giant Planets in Dusty Systems_ , _AJ_ , _154_ , 245.
  * _Michel et al._ (2021) Michel A., van der Marel N., and Matthews B. (2021) _Bridging the gap between protoplanetary and debris disks: evidence for slow disk dissipation_ , _arXiv e-prints_ , arXiv:2104.05894.
  * _Micheli et al._ (2018) Micheli M., Farnocchia D., Meech K. J. et al. (2018) _Non-gravitational acceleration in the trajectory of 1I/2017 U1 (’Oumuamua)_ , _Nature_ , _559_ , 223–226.
  * _Miller et al._ (2022) Miller D., Duvigneaud F., Menken W. et al. (2022) _High-performance solar sails for interstellar object rendezvous_ , _Acta Astronautica_ , _200_ , 242–252.
  * _Minton and Malhotra_ (2010) Minton D. A. and Malhotra R. (2010) _Dynamical erosion of the asteroid belt and implications for large impacts in the inner Solar System_ , _Icarus_ , _207_ , 744–757.
  * _Miret-Roig et al._ (2022) Miret-Roig N., Bouy H., Raymond S. N. et al. (2022) _A rich population of free-floating planets in the Upper Scorpius young stellar association_ , _Nature Astronomy_ , _6_ , 89–97.
  * _Montgomery and Welsh_ (2017) Montgomery S. L. and Welsh B. Y. (2017) _Unusually high circumstellar absorption variability around the $\delta$ Scuti /$\lambda$ Boötis star HD 183324_, _MNRAS_ , _468_ , L55–L58.
  * _Moór et al._ (2017) Moór A., Curé M., Kóspál Á. et al. (2017) _Molecular Gas in Debris Disks around Young A-type Stars_ , _ApJ_ , _849_ , 123.
  * _Morbidelli et al._ (2020) Morbidelli A., Batygin K., Brasser R. et al. (2020) _No evidence for interstellar planetesimals trapped in the Solar system_ , _MNRAS_ , _497_ , L46–L49.
  * _Morbidelli et al._ (2018) Morbidelli A., Nesvorny D., Laurenz V. et al. (2018) _The timeline of the lunar bombardment: Revisited_ , _Icarus_ , _305_ , 262–276.
  * _Morbidelli and Raymond_ (2016) Morbidelli A. and Raymond S. N. (2016) _Challenges in planet formation_ , _Journal of Geophysical Research (Planets)_ , _121_ , 1962–1980.
  * _Morbidelli et al._ (2007) Morbidelli A., Tsiganis K., Crida A. et al. (2007) _Dynamics of the Giant Planets of the Solar System in the Gaseous Protoplanetary Disk and Their Relationship to the Current Orbital Architecture_ , _AJ_ , _134_ , 1790–1798.
  * _Moro-Martín_ (2019a) Moro-Martín A. (2019a) _Could 1I/’Oumuamua be an Icy Fractal Aggregate?_ , _ApJ_ , _872_ , L32.
  * _Moro-Martín_ (2019b) Moro-Martín A. (2019b) _Origin of 1I/’Oumuamua. II. An Ejected Exo-Oort Cloud Object?_ , _AJ_ , _157_ , 86.
  * _Moro-Martín et al._ (2015) Moro-Martín A., Marshall J. P., Kennedy G. et al. (2015) _Does the Presence of Planets Affect the Frequency and Properties of Extrasolar Kuiper Belts? Results from the Herschel Debris and Dunes Surveys_ , _ApJ_ , _801_ , 143.
  * _Moro-Martín and Norman_ (2022) Moro-Martín A. and Norman C. (2022) _Interstellar Planetesimals: Potential Seeds for Planet Formation?_ , _ApJ_ , _924_ , 96.
  * _Morrison and Malhotra_ (2015) Morrison S. and Malhotra R. (2015) _Planetary Chaotic Zone Clearing: Destinations and Timescales_ , _ApJ_ , _799_ , 41.
  * _Mróz et al._ (2017) Mróz P., Udalski A., Skowron J. et al. (2017) _No large population of unbound or wide-orbit Jupiter-mass planets_ , _Nature_ , _548_ , 183–186.
  * _Mulders et al._ (2021) Mulders G. D., Pascucci I., Ciesla F. J. et al. (2021) _The Mass Budgets and Spatial Scales of Exoplanet Systems and Protoplanetary Disks_ , _arXiv e-prints_ , arXiv:2107.12520.
  * _Mumma et al._ (1993) Mumma M. J., Weissman P. R., and Stern S. A. (1993) in _Protostars and Planets III_ (E. H. Levy and J. I. Lunine, eds.), p. 1177.
  * _Musci et al._ (2012) Musci R., Weryk R. J., Brown P. et al. (2012) _An Optical Survey for Millimeter-sized Interstellar Meteoroids_ , _ApJ_ , _745_ , 161.
  * _Najita and Kenyon_ (2014) Najita J. R. and Kenyon S. J. (2014) _The mass budget of planet-forming discs: isolating the epoch of planetesimal formation_ , _MNRAS_ , _445_ , 3315–3329.
  * _Najita et al._ (2022) Najita J. R., Kenyon S. J., and Bromley B. C. (2022) _From Pebbles and Planetesimals to Planets and Dust: The Protoplanetary Disk-Debris Disk Connection_ , _ApJ_ , _925_ , 45.
  * _Namouni and Morais_ (2020) Namouni F. and Morais M. H. M. (2020) _An interstellar origin for high-inclination Centaurs_ , _MNRAS_ , _494_ , 2191–2199.
  * _Napier et al._ (2021) Napier K. J., Adams F. C., and Batygin K. (2021) _On the Fate of Interstellar Objects Captured by Our Solar System_ , __,_2_ , 217\.
  * _Neufeld et al._ (2011) Neufeld D. A., González-Alfonso E., Melnick G. et al. (2011) _The Widespread Occurrence of Water Vapor in the Circumstellar Envelopes of Carbon-rich Asymptotic Giant Branch Stars: First Results from a Survey with Herschel/HIFI_ , _ApJ_ , _727_ , L29.
  * _Norfolk et al._ (2021) Norfolk B. J., Maddison S. T., Marshall J. P. et al. (2021) _Four new planetesimals around typical and pre-main-sequence stars (PLATYPUS) debris discs at 8.8 mm_ , _MNRAS_ , _507_ , 3139–3147.
  * _O’Brien and Greenberg_ (2003) O’Brien D. P. and Greenberg R. (2003) _Steady-state size distributions for collisional populations:. analytical solution with size-dependent strength_ , _Icarus_ , _164_ , 334–345.
  * _Opitom et al._ (2019) Opitom C., Fitzsimmons A., Jehin E. et al. (2019) _2I/Borisov: A C 2-depleted interstellar comet_, _A &A_, _631_ , L8.
  * _Opitom et al._ (2021) Opitom C., Jehin E., Hutsemékers D. et al. (2021) _The similarity of the interstellar comet 2I/Borisov to Solar System comets from high-resolution optical spectroscopy_ , _A &A_, _650_ , L19.
  * _‘Oumuamua ISSI Team et al._ (2019) ‘Oumuamua ISSI Team, Bannister M. T., Bhandare A. et al. (2019) _The natural history of ‘Oumuamua_ , _Nature Astronomy_ , _3_ , 594–602.
  * _Pan et al._ (2016) Pan M., Nesvold E. R., and Kuchner M. J. (2016) _Apocenter Glow in Eccentric Debris Disks: Implications for Fomalhaut and $\varepsilon$ Eridani_, _ApJ_ , _832_ , 81.
  * _Pan and Schlichting_ (2012) Pan M. and Schlichting H. E. (2012) _Self-consistent Size and Velocity Distributions of Collisional Cascades_ , _ApJ_ , _747_ , 113\.
  * _Pascucci et al._ (2016) Pascucci I., Testi L., Herczeg G. J. et al. (2016) _A Steeper than Linear Disk Mass-Stellar Mass Scaling Relation_ , _ApJ_ , _831_ , 125\.
  * _Pawellek et al._ (2021) Pawellek N., Wyatt M., Matrà L. et al. (2021) _A $\sim$75 per cent occurrence rate of debris discs around F stars in the $\beta$ Pic moving group_, _MNRAS_ , _502_ , 5390–5416.
  * _Pearce et al._ (2022) Pearce T. D., Launhardt R., Ostermann R. et al. (2022) _Planet populations inferred from debris discs. Insights from 178 debris systems in the ISPY, LEECH, and LIStEN planet-hunting surveys_ , _A &A_, _659_ , A135.
  * _Pearce and Wyatt_ (2015) Pearce T. D. and Wyatt M. C. (2015) _Double-ringed debris discs could be the work of eccentric planets: explaining the strange morphology of HD 107146_ , _MNRAS_ , _453_ , 3329–3340.
  * _Petit et al._ (2001) Petit J.-M., Morbidelli A., and Chambers J. (2001) _The Primordial Excitation and Clearing of the Asteroid Belt_ , _Icarus_ , _153_ , 338–347.
  * _Pfalzner et al._ (2021a) Pfalzner S., Aizpuru Vargas L., Bhandare A. et al. (2021a) _Significant interstellar object production by close stellar flybys_ , _arXiv e-prints_ , arXiv:2104.06845.
  * _Pfalzner and Bannister_ (2019) Pfalzner S. and Bannister M. T. (2019) _A Hypothesis for the Rapid Formation of Planets_ , _ApJ_ , _874_ , L34.
  * _Pfalzner et al._ (2020) Pfalzner S., Davies M. B., Kokaia G. et al. (2020) _Oumuamuas Passing through Molecular Clouds_ , _ApJ_ , _903_ , 114.
  * _Pfalzner et al._ (2022) Pfalzner S., Dehghani S., and Michel A. (2022) _Most Planets Might Have More than 5 Myr of Time to Form_ , _ApJ_ , _939_ , L10.
  * _Pfalzner et al._ (2021b) Pfalzner S., Paterson D., Bannister M. T. et al. (2021b) _Interstellar Objects Follow the Collapse of Molecular Clouds_ , _ApJ_ , _921_ , 168.
  * _Pierens and Nelson_ (2008) Pierens A. and Nelson R. P. (2008) _Constraints on resonant-trapping for two planets embedded in a protoplanetary disc_ , _A &A_, _482_ , 333–340.
  * _Pinilla et al._ (2017) Pinilla P., Pohl A., Stammler S. M. et al. (2017) _Dust Density Distribution and Imaging Analysis of Different Ice Lines in Protoplanetary Disks_ , _ApJ_ , _845_ , 68.
  * _Pollack et al._ (1996) Pollack J. B., Hubickyj O., Bodenheimer P. et al. (1996) _Formation of the Giant Planets by Concurrent Accretion of Solids and Gas_ , _Icarus_ , _124_ , 62–85.
  * _Portegies Zwart_ (2021) Portegies Zwart S. (2021) _Oort cloud Ecology. I. Extra-solar Oort clouds and the origin of asteroidal interlopers_ , _A &A_, _647_ , A136.
  * _Portegies Zwart et al._ (2018) Portegies Zwart S., Torres S., Pelupessy I. et al. (2018) _The origin of interstellar asteroidal objects like 1I/2017 U1 ‘Oumuamua_ , _MNRAS_ , _479_ , L17–L22.
  * _Raddi et al._ (2015) Raddi R., Gänsicke B. T., Koester D. et al. (2015) _Likely detection of water-rich asteroid debris in a metal-polluted white dwarf_ , _MNRAS_ , _450_ , 2083–2093.
  * _Rafikov_ (2018) Rafikov R. R. (2018) _1I/2017 ’Oumuamua-like Interstellar Asteroids as Possible Messengers from Dead Stars_ , _ApJ_ , _861_ , 35.
  * _Rafikov_ (2023) Rafikov R. R. (2023) _Radial profiles of surface density in debris discs_ , _MNRAS_ , _519_ , 5607–5622.
  * _Raghavan et al._ (2010) Raghavan D., McAlister H. A., Henry T. J. et al. (2010) _A Survey of Stellar Families: Multiplicity of Solar-type Stars_ , _ApJS_ , _190_ , 1–42.
  * _Rauer et al._ (2014) Rauer H., Catala C., Aerts C. et al. (2014) _The PLATO 2.0 mission_ , _Experimental Astronomy_ , _38_ , 249–330.
  * _Raymond et al._ (2010) Raymond S. N., Armitage P. J., and Gorelick N. (2010) _Planet-Planet Scattering in Planetesimal Disks. II. Predictions for Outer Extrasolar Planetary Systems_ , _ApJ_ , _711_ , 772–795.
  * _Raymond et al._ (2011) Raymond S. N., Armitage P. J., Moro-Martín A. et al. (2011) _Debris disks as signposts of terrestrial planet formation_ , _A &A_, _530_ , A62.
  * _Raymond et al._ (2012) Raymond S. N., Armitage P. J., Moro-Martín A. et al. (2012) _Debris disks as signposts of terrestrial planet formation. II. Dependence of exoplanet architectures on giant planet and disk properties_ , _A &A_, _541_ , A11.
  * _Raymond et al._ (2018a) Raymond S. N., Armitage P. J., and Veras D. (2018a) _Interstellar Object ’Oumuamua as an Extinct Fragment of an Ejected Cometary Planetesimal_ , _ApJ_ , _856_ , L7.
  * _Raymond et al._ (2018b) Raymond S. N., Armitage P. J., Veras D. et al. (2018b) _Implications of the interstellar object 1I/’Oumuamua for planetary dynamics and planetesimal formation_ , _MNRAS_ , _476_ , 3031–3038.
  * _Raymond and Izidoro_ (2017) Raymond S. N. and Izidoro A. (2017) _Origin of water in the inner Solar System: Planetesimals scattered inward during Jupiter and Saturn’s rapid gas accretion_ , _Icarus_ , _297_ , 134–148.
  * _Raymond et al._ (2020) Raymond S. N., Kaib N. A., Armitage P. J. et al. (2020) _Survivor Bias: Divergent Fates of the Solar System’s Ejected versus Persisting Planetesimals_ , _ApJ_ , _904_ , L4.
  * _Rebollido et al._ (2020) Rebollido I., Eiroa C., Montesinos B. et al. (2020) _Exocomets: A spectroscopic survey_ , _A &A_, _639_ , A11.
  * _Richert et al._ (2018) Richert A. J. W., Getman K. V., Feigelson E. D. et al. (2018) _Circumstellar disc lifetimes in numerous galactic young stellar clusters_ , _MNRAS_ , _477_ , 5191–5206.
  * _Rigley and Wyatt_ (2022) Rigley J. K. and Wyatt M. C. (2022) _Comet fragmentation as a source of the zodiacal cloud_ , _MNRAS_ , _510_ , 834–857.
  * _Roberge et al._ (2012) Roberge A., Chen C. H., Millan-Gabet R. et al. (2012) _The Exozodiacal Dust Problem for Direct Observations of Exo-Earths_ , _PASP_ , _124_ , 799.
  * _Roberge et al._ (2000) Roberge A., Feldman P. D., Lagrange A. M. et al. (2000) _High-Resolution Hubble Space Telescope STIS Spectra of C I and CO in the $\beta$ Pictoris Circumstellar Disk_, _ApJ_ , _538_ , 904–910.
  * _Roberge et al._ (2006) Roberge A., Feldman P. D., Weinberger A. J. et al. (2006) _Stabilization of the disk around $\beta$Pictoris by extremely carbon-rich gas_, _Nature_ , _441_ , 724–726.
  * _Roberge et al._ (2014) Roberge A., Welsh B. Y., Kamp I. et al. (2014) _Volatile-rich Circumstellar Gas in the Unusual 49 Ceti Debris Disk_ , _ApJ_ , _796_ , L11.
  * _Russell_ (1916) Russell H. N. (1916) _On the Albedo of the Planets and Their Satellites_ , _ApJ_ , _43_ , 173–196.
  * _Saavik Ford and Neufeld_ (2001) Saavik Ford K. E. and Neufeld D. A. (2001) _Water Vapor in Carbon-rich Asymptotic Giant Branch Stars from the Vaporization of Icy Orbiting Bodies_ , _ApJ_ , _557_ , L113–L116.
  * _Safronov_ (1972) Safronov V. S. (1972) in _The Motion, Evolution of Orbits, and Origin of Comets_ (G. A. Chebotarev, E. I. Kazimirchak-Polonskaia, and B. G. Marsden, eds.), vol. 45, p. 329.
  * _Sánchez et al._ (2021) Sánchez J. P., Morante D., Hermosin P. et al. (2021) _ESA F-Class Comet Interceptor: Trajectory design to intercept a yet-to-be-discovered comet_ , _Acta Astronautica_ , _188_ , 265–277.
  * _Sanchis et al._ (2021) Sanchis E., Testi L., Natta A. et al. (2021) _Measuring the ratio of the gas and dust emission radii of protoplanetary disks in the Lupus star-forming region_ , _arXiv e-prints_ , arXiv:2101.11307.
  * _Schleicher_ (2008) Schleicher D. G. (2008) _The Extremely Anomalous Molecular Abundances of Comet 96p/Machholz 1 from Narrowband Photometry_ , _AJ_ , _136_ , 2204–2213.
  * _Schneider et al._ (2014) Schneider G., Grady C. A., Hines D. C. et al. (2014) _Probing for Exoplanets Hiding in Dusty Debris Disks: Disk Imaging, Characterization, and Exploration with HST/STIS Multi-roll Coronagraphy_ , _AJ_ , _148_ , 59\.
  * _Schüppler et al._ (2016) Schüppler C., Krivov A. V., Löhne T. et al. (2016) _Origin and evolution of two-component debris discs and an application to the q 1 Eridani system_, _MNRAS_ , _461_ , 2146–2154.
  * _Schwamb et al._ (2023) Schwamb M. E., Jones R. L., Yoachim P. et al. (2023) _Tuning the Legacy Survey of Space and Time (LSST) Observing Strategy for Solar System Science_ , _arXiv e-prints_ , arXiv:2303.02355.
  * _National Academies of Sciences and Medicine_ (2022) National Academies of Sciences E. and Medicine (2022) _Origins, Worlds, and Life: A Decadal Strategy for Planetary Science and Astrobiology 2023-2032_ , The National Academies Press, Washington, DC.
  * _Sekanina_ (1976) Sekanina Z. (1976) _A Probability of Encounter with Interstellar Comets and the Likelihood of their Existence_ , _Icarus_ , _27_ , 123–133.
  * _Seligman and Laughlin_ (2018) Seligman D. and Laughlin G. (2018) _The Feasibility and Benefits of In Situ Exploration of ‘Oumuamua-like Objects_ , _AJ_ , _155_ , 217.
  * _Seligman and Laughlin_ (2020) Seligman D. and Laughlin G. (2020) _Evidence that 1I/2017 U1 (’Oumuamua) was Composed of Molecular Hydrogen Ice_ , _ApJ_ , _896_ , L8.
  * _Seligman et al._ (2022a) Seligman D. Z., Becker J., Adams F. C. et al. (2022a) _Inferring Late-stage Enrichment of Exoplanet Atmospheres from Observed Interstellar Comets_ , _ApJ_ , _933_ , L7.
  * _Seligman et al._ (2021) Seligman D. Z., Levine W. G., Cabot S. H. C. et al. (2021) _On the Spin Dynamics of Elongated Minor Bodies with Applications to a Possible Solar System Analogue Composition for ’Oumuamua_ , _ApJ_ , _920_ , 28.
  * _Seligman et al._ (2022b) Seligman D. Z., Rogers L. A., Cabot S. H. C. et al. (2022b) _The Volatile Carbon-to-oxygen Ratio as a Tracer for the Formation Locations of Interstellar Comets_ , __,_3_ , 150.
  * _Sellek et al._ (2020) Sellek A. D., Booth R. A., and Clarke C. J. (2020) _The evolution of dust in discs influenced by external photoevaporation_ , _MNRAS_ , _492_ , 1279–1294.
  * _Sepulveda et al._ (2019) Sepulveda A. G., Matrà L., Kennedy G. M. et al. (2019) _The REASONS Survey: Resolved Millimeter Observations of a Large Debris Disk around the Nearby F Star HD 170773_ , _ApJ_ , _881_ , 84.
  * _Shannon et al._ (2015) Shannon A., Jackson A. P., Veras D. et al. (2015) _Eight billion asteroids in the Oort cloud_ , _MNRAS_ , _446_ , 2059–2064.
  * _Sibthorpe et al._ (2018) Sibthorpe B., Kennedy G. M., Wyatt M. C. et al. (2018) _Analysis of the Herschel DEBRIS Sun-like star sample_ , _MNRAS_ , _475_ , 3046–3064.
  * _Simon et al._ (2022) Simon J. B., Blum J., Birnstiel T. et al. (2022) _Comets and Planetesimal Formation_ , _arXiv e-prints_ , arXiv:2212.04509.
  * _Siraj and Loeb_ (2019) Siraj A. and Loeb A. (2019) _Identifying Interstellar Objects Trapped in the Solar System through Their Orbital Parameters_ , _ApJ_ , _872_ , L10.
  * _Siraj and Loeb_ (2022) Siraj A. and Loeb A. (2022) _A Meteor of Apparent Interstellar Origin in the CNEOS Fireball Catalog_ , _ApJ_ , _939_ , 53.
  * _Slettebak_ (1975) Slettebak A. (1975) _Some interesting bright southern stars of early type._ , _ApJ_ , _197_ , 137–138.
  * _Smith and Terrile_ (1984) Smith B. A. and Terrile R. J. (1984) _A Circumstellar Disk around $\beta$ Pictoris_, _Science_ , _226_ , 1421–1424.
  * _Snodgrass et al._ (2011) Snodgrass C., Fitzsimmons A., Lowry S. C. et al. (2011) _The size distribution of Jupiter Family comet nuclei_ , _MNRAS_ , _414_ , 458–469.
  * _Snodgrass and Jones_ (2019) Snodgrass C. and Jones G. H. (2019) _The European Space Agency’s Comet Interceptor lies in wait_ , _Nature Communications_ , _10_ , 5418\.
  * _Sosa and Fernández_ (2011) Sosa A. and Fernández J. A. (2011) _Masses of long-period comets derived from non-gravitational effects - analysis of the computed results and the consistency and reliability of the non-gravitational parameters_ , _MNRAS_ , _416_ , 767–782.
  * _Steckloff et al._ (2021) Steckloff J. K., Lisse C. M., Safrit T. K. et al. (2021) _The sublimative evolution of (486958) Arrokoth_ , _Icarus_ , _356_ , 113998\.
  * _Stephan et al._ (2017) Stephan A. P., Naoz S., and Zuckerman B. (2017) _Throwing Icebergs at White Dwarfs_ , _ApJ_ , _844_ , L16.
  * _Sterken et al._ (2019) Sterken V. J., Westphal A. J., Altobelli N. et al. (2019) _Interstellar Dust in the Solar System_ , _Space Sci. Rev._ , _215_ , 43.
  * _Stern_ (1990) Stern S. A. (1990) _ISM-induced erosion and gas-dynamical drag in the Oort Cloud_ , _Icarus_ , _84_ , 447–466.
  * _Stern_ (2003) Stern S. A. (2003) _The evolution of comets in the Oort cloud and Kuiper belt_ , _Nature_ , _424_ , 639–642.
  * _Stern et al._ (1990) Stern S. A., Shull J. M., and Brandt J. C. (1990) _Evolution and detectability of comet clouds during post-main-sequence stellar evolution_ , _Nature_ , _345_ , 305–308.
  * _Stern et al._ (1991) Stern S. A., Stocke J., and Weissman P. R. (1991) _An IRAS search for Extra-Solar Oort Clouds_ , _Icarus_ , _91_ , 65–75.
  * _Strøm et al._ (2020) Strøm P. A., Bodewits D., Knight M. M. et al. (2020) _Exocomets from a Solar System Perspective_ , _PASP_ , _132_ , 101001.
  * _Strubbe and Chiang_ (2006) Strubbe L. E. and Chiang E. I. (2006) _Dust Dynamics, Surface Brightness Profiles, and Thermal Spectra of Debris Disks: The Case of AU Microscopii_ , _ApJ_ , _648_ , 652–665.
  * _Su et al._ (2006) Su K. Y. L., Rieke G. H., Stansberry J. A. et al. (2006) _Debris Disk Evolution around A Stars_ , _ApJ_ , _653_ , 675–689.
  * _Sugiura et al._ (2019) Sugiura K., Kobayashi H., and Inutsuka S.-i. (2019) _Collisional elongation: Possible origin of extremely elongated shape of 1I/’Oumuamua_ , _Icarus_ , _328_ , 14–22.
  * _Telesco et al._ (2005) Telesco C. M., Fisher R. S., Wyatt M. C. et al. (2005) _Mid-infrared images of $\beta$ Pictoris and the possible role of planetesimal collisions in the central disk_, _Nature_ , _433_ , 133–136.
  * _Terebey et al._ (1984) Terebey S., Shu F. H., and Cassen P. (1984) _The collapse of the cores of slowly rotating isothermal clouds_ , _ApJ_ , _286_ , 529–551.
  * _Thébault and Beust_ (2001) Thébault P. and Beust H. (2001) _Falling evaporating bodies in the $\beta$ Pictoris system. Resonance refilling and long term duration of the phenomenon_, _A &A_, _376_ , 621–640.
  * _Throop and Bally_ (2005) Throop H. B. and Bally J. (2005) _Can Photoevaporation Trigger Planetesimal Formation?_ , _ApJ_ , _623_ , L149–L152.
  * _Trilling et al._ (2018) Trilling D. E., Mommert M., Hora J. L. et al. (2018) _Spitzer Observations of Interstellar Object 1I/‘Oumuamua_ , _AJ_ , _156_ , 261.
  * _Trilling et al._ (2017) Trilling D. E., Robinson T., Roegge A. et al. (2017) _Implications for Planetary System Formation from Interstellar Object 1I/2017 U1 (‘Oumuamua)_ , _ApJ_ , _850_ , L38.
  * _Tychoniec et al._ (2020) Tychoniec Ł., Manara C. F., Rosotti G. P. et al. (2020) _Dust masses of young disks: constraining the initial solid reservoir for planet formation_ , _A &A_, _640_ , A19.
  * _Valtonen and Zheng_ (1990) Valtonen M. and Zheng J. Q. (1990) in _Nordic-Baltic Astronomy Meeting_ (C. I. Lagerkvist, D. Kiselman, and M. Lindgren, eds.), pp. 353–360.
  * _Valtonen and Innanen_ (1982) Valtonen M. J. and Innanen K. A. (1982) _The capture of interstellar comets_ , _ApJ_ , _255_ , 307–315.
  * _Vavilov and Medvedev_ (2019) Vavilov D. E. and Medvedev Y. D. (2019) _Dust bombardment can explain the extremely elongated shape of 1I/’Oumuamua and the lack of interstellar objects_ , _MNRAS_ , _484_ , L75–L78.
  * _Veras_ (2016) Veras D. (2016) _Post-main-sequence planetary system evolution_ , _Royal Society Open Science_ , _3_ , 150571.
  * _Veras et al._ (2020) Veras D., Reichert K., Flammini Dotti F. et al. (2020) _Linking the formation and fate of exo-Kuiper belts within Solar system analogues_ , _MNRAS_ , _493_ , 5062–5078.
  * _Villaver et al._ (2014) Villaver E., Livio M., Mustill A. J. et al. (2014) _Hot Jupiters and Cool Stars_ , _ApJ_ , _794_ , 3.
  * _Vitense et al._ (2012) Vitense C., Krivov A. V., Kobayashi H. et al. (2012) _An improved model of the Edgeworth-Kuiper debris disk_ , _A &A_, _540_ , A30.
  * _Wahhaj et al._ (2016) Wahhaj Z., Milli J., Kennedy G. et al. (2016) _The SHARDDS survey: First resolved image of the HD 114082 debris disk in the Lower Centaurus Crux with SPHERE_ , _A &A_, _596_ , L4.
  * _Weissman_ (1996) Weissman P. R. (1996) in _Completing the Inventory of the Solar System_ (T. Rettig and J. M. Hahn, eds.), vol. 107 of _Astronomical Society of the Pacific Conference Series_ , pp. 265–288.
  * _Weissman_ (1999) Weissman P. R. (1999) _Diversity of Comets: Formation Zones and Dynamical Paths_ , _Space Sci. Rev._ , _90_ , 301–311.
  * _Westphal et al._ (2014) Westphal A. J., Stroud R. M., Bechtel H. A. et al. (2014) _Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft_ , _Science_ , _345_ , 786–791.
  * _Williams and Cieza_ (2011) Williams J. P. and Cieza L. A. (2011) _Protoplanetary Disks and Their Evolution_ , _ARA &A_, _49_ , 67–117.
  * _Wilson et al._ (2019) Wilson P. A., Kerr R., Lecavelier des Etangs A. et al. (2019) _Detection of nitrogen gas in the $\beta$ Pictoris circumstellar disc_, _A &A_, _621_ , A121.
  * _Witze_ (2019) Witze A. (2019) _Hawaiian-language experts make their mark on the Solar System_ , _Nature_ , _565_ , 278–279.
  * _Wyatt_ (2003) Wyatt M. C. (2003) _Resonant Trapping of Planetesimals by Planet Migration: Debris Disk Clumps and Vega’s Similarity to the Solar System_ , _ApJ_ , _598_ , 1321–1340.
  * _Wyatt_ (2008) Wyatt M. C. (2008) _Evolution of debris disks._ , _ARA &A_, _46_ , 339–383.
  * _Wyatt et al._ (2007) Wyatt M. C., Clarke C. J., and Greaves J. S. (2007) _Origin of the metallicity dependence of exoplanet host stars in the protoplanetary disc mass distribution_ , _MNRAS_ , _380_ , 1737–1743.
  * _Wyatt et al._ (1999) Wyatt M. C., Dermott S. F., Telesco C. M. et al. (1999) _How Observations of Circumstellar Disk Asymmetries Can Reveal Hidden Planets: Pericenter Glow and Its Application to the HR 4796 Disk_ , _ApJ_ , _527_ , 918–944.
  * _Wyatt et al._ (2012) Wyatt M. C., Kennedy G., Sibthorpe B. et al. (2012) _Herschel imaging of 61 Vir: implications for the prevalence of debris in low-mass planetary systems_ , _MNRAS_ , _424_ , 1206–1223.
  * _Wyatt et al._ (2015) Wyatt M. C., Panić O., Kennedy G. M. et al. (2015) _Five steps in the evolution from protoplanetary to debris disk_ , _Ap &SS_, _357_ , 103.
  * _Xing et al._ (2020) Xing Z., Bodewits D., Noonan J. et al. (2020) _Water Production Rates and Activity of Interstellar Comet 2I/Borisov_ , _ApJ_ , _893_ , L48.
  * _Xu et al._ (2019) Xu S., Dufour P., Klein B. et al. (2019) _Compositions of Planetary Debris around Dusty White Dwarfs_ , _AJ_ , _158_ , 242.
  * _Ye et al._ (2020) Ye Q., Kelley M. S. P., Bolin B. T. et al. (2020) _Pre-discovery Activity of New Interstellar Comet 2I/Borisov beyond 5 au_ , _AJ_ , _159_ , 77.
  * _Yelverton et al._ (2020) Yelverton B., Kennedy G. M., and Su K. Y. L. (2020) _No significant correlation between radial velocity planet presence and debris disc properties_ , _MNRAS_ , _495_ , 1943–1957.
  * _Youdin and Goodman_ (2005) Youdin A. N. and Goodman J. (2005) _Streaming Instabilities in Protoplanetary Disks_ , _ApJ_ , _620_ , 459–469.
  * _Zellner_ (2017) Zellner N. E. B. (2017) _Cataclysm No More: New Views on the Timing and Delivery of Lunar Impactors_ , _Origins of Life and Evolution of the Biosphere_ , _47_ , 261–280.
  * _Zhang_ (2018) Zhang Q. (2018) _Prospects for Backtracing 1I/‘Oumuamua and Future Interstellar Objects_ , _ApJ_ , _852_ , L13.
  * _Zhang and Lin_ (2020) Zhang Y. and Lin D. N. C. (2020) _Tidal fragmentation as the origin of 1I/2017 U1 (‘Oumuamua)_ , _Nature Astronomy_ , _4_ , 852–860.
  * _Zhao et al._ (2021) Zhao Y., Rezac L., Skorov Y. et al. (2021) _Sublimation as an effective mechanism for flattened lobes of (486958) Arrokoth_ , _Nature Astronomy_ , _5_ , 139–144.
  * _Zheng et al._ (1990) Zheng J.-Q., Valtonen M. J., and Valtaoja L. (1990) _Capture of Comets during the Evolution of a Star Cluster and the Origin of the Oort Cloud_ , _Celestial Mechanics and Dynamical Astronomy_ , _49_ , 265–272.
  * _Zieba et al._ (2019) Zieba S., Zwintz K., Kenworthy M. A. et al. (2019) _Transiting exocomets detected in broadband light by TESS in the $\beta$ Pictoris system_, _A &A_, _625_ , L13.
  * _Zuckerman et al._ (1995) Zuckerman B., Forveille T., and Kastner J. H. (1995) _Inhibition of giant-planet formation by rapid gas depletion around young stars_ , _Nature_ , _373_ , 494–496.
  * _Zuckerman and Song_ (2012) Zuckerman B. and Song I. (2012) _A 40 Myr Old Gaseous Circumstellar Disk at 49 Ceti: Massive CO-rich Comet Clouds at Young A-type Stars_ , _ApJ_ , _758_ , 77.