Draft version July 14, 2025

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The Kinematic Age of 3I/ATLAS and its Implications for Early Planet Formation
1, ∗ 2, †
Aster G. Taylor and Darryl Z. Seligman
1 Dept. of Astronomy, University of Michigan, Ann Arbor, MI 48109, USA
2 Department of Physics and Astronomy, Michigan State University, East Lansing, MI 48824, USA

ABSTRACT
The recent discovery of the third interstellar object (3I/ATLAS) expands the known census from two
arXiv:2507.08111v1 [astro-ph.EP] 10 Jul 2025

to three and significantly improves statistical inferences regarding the underlying galactic population.
3I/ATLAS exhibits detectable activity that may increase as the object approaches perihelion. In this
paper, we argue that the cometary activity likely significantly contributes to 3I/ATLAS’s brightness,
since the nuclear size of 3I/ATLAS assuming an asteroidal reflectance implies an untenable interstellar
object mass per star. 3I/ATLAS exhibits an excess velocity of v∞ = 58 km/s relative to the Sun which
is significantly larger than that of 1I/‘Oumuamua or 2I/Borisov. This velocity implies that 3I/ATLAS
is relatively old in comparison to previous interstellar objects. Here, we calculate the posterior distri-
bution of ages implied by the kinematics of the interstellar objects and find that 3I/ATLAS is likely
∼ 3 − 11 Gyr old, assuming that the interstellar object and stellar age-velocity relations are equivalent.
We also calculate the distribution of host star metallicities and find that 3I/ATLAS likely originated in
a lower-metallicity system than the previous interstellar objects. These results show that interstellar
object formation is likely efficient at low metallicities and early in the history of the Galaxy. Finally,
we estimate and approximate interstellar object formation rate throughout Galactic history implied
by these three objects.

Keywords: Interstellar Objects (52) — Asteroids (72) — Comets (280)

1. INTRODUCTION to three objects, the discovery of 3I/ATLAS expands

The third interstellar object, 3I/ATLAS, was recently this sample by 50 % improves the robustness of these
discovered traversing through the solar system ( MPEC sample-limited statistics. In an ensemble, however, the
2025; D. Z. Seligman et al. 2025). This discovery follows kinematics and chemodynamics of Galactic interstellar
the discoveries of 1I/‘Oumuamua in 2017 ( MPEC 2017; object streams will trace the history of Galactic star for-
G. V. Williams et al. 2017) and 2I/Borisov in 2019 (G. mation, which has been investigated theoretically by S.
Borisov et al. 2019). These objects possibly formed in Portegies Zwart (2021); C. Lintott et al. (2022); M. J.
protoplanetary disks and were subsequently ejected via Hopkins et al. (2023); J. C. Forbes et al. (2024); M. J.
planet scattering or post–main sequence mass loss (S. Hopkins et al. (2025).
Portegies Zwart et al. 2018; A. Do et al. 2018; W. G. This discovery is especially relevant given the myste-
Levine et al. 2023). rious and divergent properties of the first two interstel-
Although the precise system that produced a given in- lar objects. In particular, 1I/‘Oumuamua exhibited sig-
terstellar object is impossible to determine (T. Hallatt & nificant nongravitational acceleration (M. Micheli et al.
P. Wiegert 2020), these objects provide a unique oppor- 2018) but had no visible activity (K. J. Meech et al.
tunity to directly observe material formed in extrasolar 2017; D. Jewitt et al. 2017; D. E. Trilling et al. 2018).
systems. Given the difficulty of directly identifying an At the same time, 1I/‘Oumuamua exhibited significant
origin, statistical analyses are necessary to understand brightness variations with a period of 4.3 hr (M. J. S.
the population of interstellar objects. By going from two Belton et al. 2018), indicating a rotating elongated body.
Absolute magnitude variations further indicated that
1I/‘Oumuamua was experiencing complex, nonprincipal
Email: agtaylor@umich.edu axis rotation (M. Drahus et al. 2017; K. J. Meech et al.
∗ Fannie and John Hertz Foundation Fellow
† NSF Astronomy and Astrophysics Postdoctoral Fellow
2017; W. C. Fraser et al. 2018; A. G. Taylor et al. 2023)
and had an extreme oblate shape (S. Mashchenko 2019).
2

The complex properties of 1I/‘Oumuamua led to a In addition, the excess velocities of 1I/‘Oumuamua
wide variety of hypothesized origins. While some au- (v∞ = 26 km/s) and 2I/Borisov (v∞ = 32 km/s) in-
thors suggested that a low-density fractal aggregate (A. dicated distinct ages of ∼100 Myr and ∼1 Gyr, respec-
Moro-Martı́n 2019; E. G. Flekkøy et al. 2019) or an tively (E. Mamajek 2017; E. Gaidos et al. 2017; F. Feng
ultra-thin geometry (S. Bialy & A. Loeb 2018) would & H. R. A. Jones 2018; T. Hallatt & P. Wiegert 2020; C.-
allow radiation pressure to explain the nongravitational H. Hsieh et al. 2021). 3I/ATLAS is a significant outlier
acceleration , others demonstrated that low dust produc- in this respect, with an excess velocity of v∞ = 58 km/s.
tion during outgassing could also be responsible (e.g., Z. A similar scaling would indicate that 3I/ATLAS has an
Sekanina 2019). age of ∼10 Gyr, although this is based on a rough com-
While H2 O ice is the most common solar system comet parison between excess velocity and stellar velocity dis-
volatile (e.g., M. F. A’Hearn et al. 2012; A. L. Cochran persion and is inherently approximate. Our current un-
et al. 2015) and is consistent with observations (D. E. derstanding of 1I/‘Oumuamua and 2I/Borisov has been
Trilling et al. 2018; R. S. Park et al. 2018), energy con- reviewed in A. Moro-Martı́n (2022); A. Fitzsimmons
straints implied that H2 O could not be responsible for et al. (2023); D. Z. Seligman & A. Moro-Martı́n (2023),
the nongravitational acceleration (Z. Sekanina 2019). and D. Jewitt & D. Z. Seligman (2023).
Constraints on CO and CO2 outgassing from the Spitzer In this work, we provide interstellar object popula-
Space Telescope (D. E. Trilling et al. 2018) imply that tion calculations incorporating 3I/ATLAS. In Sec. 2,
some other, more exotic volatile must be responsible for we argue that 3I/ATLAS must have a smaller size than
the nongravitational acceleration. Therefore, N2 (A. P. currently measured, somewhat comparable to that of
Jackson & S. J. Desch 2021; S. J. Desch & A. P. Jack- 2I/Borisov. Next, we consider the Galactic velocity ra-
son 2021) or H2 (D. Seligman & G. Laughlin 2020; J. B. diants of the three interstellar objects and calculate the
Bergner & D. Z. Seligman 2023) outgassing have also probability density functions of their ages implied by
been proposed as solutions, although the provenance of these velocities in Sec. 3. In Sec. 4, we calculate the
such compositions are debated (see, e.g., D. Seligman & distribution of stellar metallicities that these ages imply.
G. Laughlin 2020; C.-H. Hsieh et al. 2021; W. G. Levine We then approximate the interstellar object formation
& G. Laughlin 2021; S. J. Desch & A. P. Jackson 2022; rate in Sec. 5 and finally conclude and discuss our re-
J. B. Bergner & D. Z. Seligman 2023). It has been sug- sults in Sec. 6.
gested that 1I/‘Oumuamua formed in giant molecular
cloud instead (D. Seligman & G. Laughlin 2020; C.-H. 2. ESTIMATED NUMBER DENSITY AND SIZE
Hsieh et al. 2021; W. G. Levine & G. Laughlin 2021).
We calculate an approximate number density by
Meanwhile, the properties of 2I/Borisov were more
assuming that the detection rate for an object like
typical for a comet. The object displayed distinct
3I/ATLAS is Γ = 0.1 yr−1 . This value reflects the time
cometary activity and exhibited a volatile composition
that the ATLAS survey has been online, especially when
broadly similar to that of some solar system comets (Z.
combined with the Pan-STARRS1 survey (K. C. Cham-
Xing et al. 2020; H. W. Lin et al. 2020; M. T. Ban-
bers et al. 2016) and the Catalina Sky Survey, which
nister et al. 2020). However, the volatile composition
are also sensitive to objects of this magnitude. Now,
was enriched in CO relative to H2 O (D. Bodewits et al.
the ATLAS survey detects all objects down to an appar-
2020; M. A. Cordiner et al. 2020; T. Kareta et al. 2020).
ent magnitude of 19. Since 3I/ATLAS has an absolute
2I/Borisov also exhibited a (predicted, D. Jewitt & J.
magnitude of 12, an object with H ≤ 12 is detectable by
Luu 2019a,b) spin-up due to its outgassing, which lead
ATLAS at a distance of approximately d = 5 au, corre-
to an outburst and disintegration event post-perihelion
sponding to a detection cross-section of σ = πd2 . Since
(D. Jewitt et al. 2020). While observations are still
3I/ATLAS is moving at v∞ = 58 km/s, the total num-
ongoing, 3I/ATLAS exhibits an active coma similar to
ber density is n = Γ/(σv∞ ) ≃ 10−4 au−3 . This value
that of 2I/Borisov (M. R. Alarcon et al. 2025; D. Je-
is comparable to the previous estimate of 3 × 10−4 au−3
witt & J. Luu 2025; D. Z. Seligman et al. 2025; C.
(D. Z. Seligman et al. 2025) if slightly different assump-
Opitom et al. 2025). Although the volatile composition
tions are made about the ATLAS detection area.
of such activity has not been measured yet, the spectral
However, this value implies an exceptionally high mass
slope of 3I/ATLAS is similar to that of 2I/Borisov and
of interstellar objects produced per star. If the stars
that of D-type asteroids and is consistent with that of
in the Galaxy are separated by distances of approxi-
1I/‘Oumuamua (F. E. DeMeo et al. 2009; D. Z. Seligman
mately 1.5 pc, then each star should eject 1013 interstel-
et al. 2025).
lar objects the size of 3I/ATLAS or larger. If 3I/ATLAS
were nearly rN ≃ 10 km across, at the typical cometary
 3

density of ρ = 1 g/cm3 each star must produce ap- There exists previous work (e.g., F. Almeida-
proximately 10−2 M⊙ of interstellar objects larger than Fernandes & H. J. Rocha-Pinto 2018a) calculating the
3I/ATLAS. There must be some additional mass stored age of stars based on their galactic velocities, which
in smaller objects, which will only add to this (already we will briefly summarize here. Consider a star with
significant) value. a Galactic velocity U , V , W relative to the Sun. This
It is presumably infeasible for formation processes to velocity can be converted to the independent velocity
produce this density of interstellar objects. Since the ellipsoid values v1 and v2 , which ignore the correlation
typical star is 0.5 M⊙ , this would imply that there is between U and V . Consider a single velocity value vi .
∼ 50 times the mass in stars than in interstellar objects. Stars of a given age τ will have a Gaussian distribution
When accounting for the metallicity, the interstellar ob- of vi velocities with a mean of zero relative to the LSR
jects represent the metals of nearly twice as much matter and a velocity dispersion σi (τ ). Therefore, the proba-
as is represented in stars. bility of obtaining a velocity vi from a star of age τ is
Therefore, the true size of 3I/ATLAS must be some- given by
what less than the estimated 10 km upper limit. This
v2
 
is expected, since 3I/ATLAS has been shown to be ac- 1
p(vi |τ ) = √ exp − 2i . (2)
tive even at 4.5 au. In order for 3I/ATLAS to imply a 2πσi (τ ) 2σi (τ )
mass of MISO ≃ 100 M⊙ in interstellar objects per star, Using Bayes’ theorem, the age probability distribution
3I/ATLAS must have a radius rN of (see also A. Loeb p(τ |v1 , v2 , v3 ) is given by
2025)
Y
 1/3  −1/3 p(τ |v1 , v2 , v3 ) = p(τ ) p(vi |τ ) , (3)
MISO ρ i
rN = 2.3 km . (1)
100 M⊕ 1 g/cm3
where p(τ ) is the probability of finding
R a star with age
τ . This is normalized such that p(τ |v1 , v2 , v3 )dτ = 1.
Given the activity already detected on 3I/ATLAS
Previous work (F. Almeida-Fernandes & H. J. Rocha-
(M. R. Alarcon et al. 2025; D. Jewitt & J. Luu 2025;
Pinto 2018b) has used the Geneva-Copenhagen Survey
D. Z. Seligman et al. 2025; C. Opitom et al. 2025),
(B. Nordström et al. 2004; J. Holmberg et al. 2009), an
this is a somewhat reasonable value, since the coma can
all-sky survey of F and G dwarfs in the solar neighbor-
account for a significant fraction of its brightness. If
hood, to calibrate the relationship between the stellar
3I/ATLAS’s nuclear size is closer to 2 km, then the body
kinematics and the ages. For a given U , V , and W ,
itself will have an absolute magnitude of H = 15.5.
Given that the measured absolute magnitude is H = v1 =(U + U⊙ ) cos lv (τ ) + (V + V⊙′ (τ )) sin lv (τ ) ; (4a)
12.4, the coma will account for ∼94 % of 3I/ATLAS’s
v2 =(V + V⊙′ (τ )) cos lv (τ ) − (U + U⊙ ) sin lv (τ ) ; (4b)
flux.
v3 =W + W⊙ . (4c)
3. KINEMATIC AGE
Here, U⊙ = 9.8 km/s, W⊙ = 7.2 km/s,
The excess velocity of 3I/ATLAS is nearly v∞ ≃
58 km/s relative to the Sun, significantly higher than lv (τ ) = 0.41 exp(−0.37τ ) , (5)
1I/‘Oumuamua’s velocity of 26 km/s or 2I/Borisov’s
and
32 km/s. This high velocity implies a similarly high age
V⊙′ (τ ) = 0.17τ 2 + 0.63τ + 12.5 . (6)
for 3I/ATLAS relative to the other two interstellar ob-
jects. Finally,
For a given measured velocity, we can calculate the
probability density function (PDF) of the expected ages. σ1 (τ ) =22.0τ 0.33 , (7a)
0.42
We first assume that interstellar objects have a velocity σ2 (τ ) =11.9τ , and (7b)
distribution close to that of their parent star. This is σ3 (τ ) =9.1τ 0.48
. (7c)
expected, since the stellar velocity distribution is mod-
ified over time by the effects of the Galactic potential, The velocities of the three interstellar objects in
which will have nearly identical effects on the interstellar Galactic coordinates are given in Table 1. We can there-
objects (D. Seligman & G. Laughlin 2018). With this fore determine the age distribution of the three inter-
assumption, the age PDF of an interstellar object with stellar objects. In Fig. 1, we show the probability dis-
a Galactic velocity U , V , W is equivalent to that of a tribution of the ages of the three interstellar objects.
star with the same velocity. We also show the median (vertical dashed lines) and
4

Table 1. Galactic interstellar object Velocities. The Galactic velocities of the interstellar objects.
Object U [km/s] V [km/s] W [km/s] Citation
1I/‘Oumuamua -11.457 -22.395 -7.746 E. Mamajek 2017
2I/Borisov 22.000 -23.601 1.057 J. de León et al. 2020
3I/ATLAS -51.14 -19.33 18.86 D. Z. Seligman et al. 2025

2.0
1I/'Oumuamua
1I/'Oumuamua
100 2I/Borisov
2I/Borisov
3I/ATLAS
3I/ATLAS

10 − 1 1.5
𝜏 p(𝜏)

10 − 2

p(Z)
1.0

10 − 3

0.5
10 − 4

10 − 5
10 −2 10 −1 10 0 10 1 0.0
Age 𝜏 [Gyr] −1.0 −0.5 0.0 0.5
[Fe/H]
Figure 1. interstellar object Age. The probability dis-
Figure 2. interstellar object Metallicity. The proba-
tribution function p(τ ) for the three known interstellar ob-
bility density function p(Z) for the interstellar objects as a
jects. We show the age distribution as well as the median
function of the metallicity. The median is shown as a dashed
(dashed line) and the 68 % confidence region (shaded).
line and the 68 % confidence region is shaded.

the 68 % confidence regions (shaded). We find that the

+4.40 4. PARENT STELLAR METALLICITIES
age of 1I/‘Oumuamua is τ1 = 1.24−0.98 Gyr, the age
+4.98
of 2I/Borisov is τ2 = 4.85−2.85 Gyr, and the age of Given that the Galactic metallicity increases with
3I/ATLAS is τ3 = 7.04+4.40 time, we can convert these age probability distribu-
−3.44 Gyr.
As expected, the higher the velocity of the interstellar tions into metallicity distributions. For a given age,
object, the higher its age. However, the distribution of we assume that the metallicity distribution has a uni-
ages generally overlaps far more than expected. Even form scatter of ±0.3 dex and a median value given by
1I/‘Oumuamua, the youngest interstellar object, has a Fig. 2 in V. A. Marsakov et al. (2011). Assuming that
median age significantly higher than the 30-100 Myr gen- the metallicity follows a uniform
R distribution provides
erally discussed in the literature (F. Feng & H. R. A. p(Z|τ ). Therefore, p(Z) = p(Z|τ )p(τ )dτ . With p(τ )
Jones 2018; C.-H. Hsieh et al. 2021). However, this age given by Eq. (3) and
is broadly consistent with a previous kinematical age es- 
5/3 |Z − Z (τ )| ≤ 0.3 dex;
timate of 0.01-1.87 Gyr (F. Almeida-Fernandes & H. J. p(Z|τ ) =
0
(8)
Rocha-Pinto 2018a). 0 otherwise ,
Regardless, the expected age of 3I/ATLAS is ap-
proximately 3-11 Gyr. This is a significant range, but we calculate p(Z). We show this distribution in Fig.
indicates that this object is old and is likely signifi- 2. The median parent metallicity of 1I/‘Oumuamua
cantly older than 1I/‘Oumuamua or 2I/Borisov. This is [Fe/H] = −0.08 ± 0.21, 2I/Borisov has [Fe/H] =
age is also consistent with the values predicted by the −0.15+0.22 +0.23
−0.21 , and 3I/ATLAS has [Fe/H] = −0.18−0.21 .
Ōtautahi-Oxford population model (M. J. Hopkins et al. While the three interstellar objects do not exhibit
2025), and implies that this object likely originated in significant variation in their parent stellar population
the thick disk of the Galaxy. metallicity distribution, the older objects likely origi-
nated from lower-metallicity systems. Specifically, it is
 5

100 the probability of observing each of the three known in-

terstellar objects is equal so that wi = 1/3. Given that
assumption, we can calculate the total interstellar ob-
ject production rate versus time p(τ ), which is shown in
10 − 1 Fig. 3.
We can assume that the interstellar object formation
p(𝜏) [1/Gyr]

rate is proportional to the total PDF of interstellar ob-

ject ages. This assumption is predicated on the idea
10 − 2 that if interstellar objects are destroyed over time, that
destruction rate is a constant function of the Galactic
age or is negligible in comparison to interstellar object
production (M. J. Hopkins et al. 2023, 2025). Given
10 − 3
these assumptions, Fig. 3 indicates that the interstel-
lar object production rates were relatively flat for the
first 10 Gyr of Galactic history and increased in the last
10 − 4 100 Myr. While our approximate interstellar object for-
10 −2 10 −1 10 0 10 1 mation rate then drops off to a very small production
Age 𝜏 [Gyr] rate in the last 10 Myr, this region has significant bias.
Interstellar objects with ages of 10 Myr have typical ve-
Figure 3. interstellar object Production Rate. An ap- locities of only 5 km/s and have a maximum range of
proximate interstellar object production rate, assuming that
50 pc. This sample may therefore be volume-limited,
the weight for each interstellar object is equal.
since many interstellar objects with ages τ ≤ 10 Myr
could not have made it to the solar system to be de-
not unreasonable for 3I/ATLAS to be formed around a tected.
star with a metallicity as low as −0.4 dex, which would
represent a system with fewer metals than the Sun by
6. DISCUSSION
a factor of 0.4. This result implies that interstellar ob-
ject formation processes are operating at metallicities In this paper, we have built off previous work on
somewhat lower than the Sun. The detection of plan- the ages of 1I/‘Oumuamua and 2I/Borisov (e.g., F.
ets around stars of similar metallicity ([Fe/H] = −0.68, Almeida-Fernandes & H. J. Rocha-Pinto 2018b; T. Hal-
W. D. Cochran et al. 2007) is consistent with this result. latt & P. Wiegert 2020) to calculate the kinematic age
of the new object, 3I/ATLAS. Our results indicate that
5. INTERSTELLAR OBJECT FORMATION RATE 3I/ATLAS is the oldest detected interstellar object, ap-
The fact that these interstellar objects cover a range proximately 3-11 Gyr old. 3I/ATLAS therefore provides
of possible age values implies that interstellar objects a sample of planetary system formation in the early
must be formed over a similarly wide range of ages. In- Galaxy, confirming that such systems exist and allowing
deed, we can use the expected age PDFs to estimate the us to determine how such systems may differ from the
production rate of interstellar objects over time. younger exoplanet systems currently studied. Given its
Given N observations, each of which has a PDF pi (τ ), age, this object also likely originated in the thick disk of
the total PDF of these observations is given by the Galaxy, providing a sample of system formation in
X this region.
p(τ ) = wi pi (τ ) , (9) We have also calculated the metallicity distribution
i
for the stars that may have formed each interstellar
P
where wi are the weights of the observations and wi = object. As expected, the older objects generally favor
1. The weight of each observation is determined by the lower-metallicity parents, although all metallicity distri-
probability of such an observation occurring. In this butions are similar and relatively flat. Due to the large
case, these weights will depend on the size and absolute inherent scatter in the age-metallicity relation, the in-
magnitude of the interstellar objects as well as the de- terstellar object metallicities are very broad and cannot
tection capabilities of observational telescopes. To date, be narrowed down for such a small sample. It may be
the size of 3I/ATLAS is not well-known, and so these possible to determine if interstellar objects preferentially
weights cannot be approximated here. However, given formed around stars of a certain metallicity when future
the dearth of interstellar objects and the relatively con- interstellar objects are discovered. However, this will
sistent detection rate, it is reasonable to assume that require a larger sample than is currently available.
6

In addition, the planetesimal mass budget at low Finally, we describe caveats to these results. Our cal-
metallicities is relatively limited (G. Andama et al. culations are preliminary in nature and heavily rely on
2024). If the size of 3I/ATLAS is rN = 2.3 km, then approximation. While many of these approximations are
the interstellar object mass budget for systems with a appropriate and will hold to an order-of-magnitude level,
metallicity of [Fe/H] ≃ −0.4 − 0.03 is our results will change as more interstellar objects are
detected and as the physical properties of 3I/ATLAS are
better constrained with forthcoming observations. Par-
 r
N
3 ticular caution must be taken with our calculation of the
MISO = 100 M⊕ . (10) interstellar object production rate calculation, which re-
2.3 km
lies on an equal-weight assumption and will require care-
ful consideration of the detection statistics to gain true
This predicted mass budget will vary based on the size of insight.
3I/ATLAS. Once the size of this object is established, Fortunately, we expect the recently-commissioned
it will be possible to estimate the corresponding mass Vera C. Rubin Observatory and its Legacy Survey of
budget. Space and Time (LSST) to detect many more interstel-
Regardless, we have shown that 3I/ATLAS is old and lar objects (D. J. Hoover et al. 2022; D. Marčeta & D. Z.
likely formed around a low-metallicity star. The detec- Seligman 2023; R. C. Dorsey et al. 2025). As the popu-
tion of this object therefore indicates that interstellar lation sample grows, statistical calculations will become
object formation is efficient at low metallicities and early more robust and converge. Forthcoming observations
in the history of the Galaxy. While planets have been of 3I/ATLAS will provide insight into an object that
found around low-metallicity stars (e.g., W. D. Cochran may have formed in a stellar system nearly as old as the
et al. 2007), the detection of 3I/ATLAS provides an in- Galaxy itself.
dependent confirmation of this result. ACKNOWLEDGMENTS
Lastly, we calculated the interstellar object formation We thank Gregory Laughlin and Fred Adams for in-
rate implied by these detections. Our calculation sug- sightful conversations. A.G.T. acknowledges support
gests that while interstellar object production occurred from the Fannie and John Hertz Foundation and the
early in the lifetime of the Galaxy, the interstellar object University of Michigan’s Rackham Merit Fellowship
formation rate increased for the first several Gyr before Program. D.Z.S. is supported by an NSF Astronomy
flattening out. The interstellar object formation rate and Astrophysics Postdoctoral Fellowship under award
then increased to a peak in the last ∼300 Myr before AST-2303553. This research award is partially funded
dropping off rapidly in the last 100 Myr. However, this by a generous gift of Charles Simonyi to the NSF Di-
final dropoff is complicated by a possible detection bias vision of Astronomical Sciences. The award is made in
against such young objects, which may have difficulty recognition of significant contributions to Rubin Obser-
reaching the solar system. vatory’s Legacy Survey of Space and Time.

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