Publications

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2026

1. The Two-Dimensional Structure of Circumplanetary Disks and their Radiative Signatures

   Aster G. Taylor, Fred C. Adams, and Nuria Calvet

   Icarus, Mar 2026

   Abs ADS arXiv

   0 citations

   Updated Apr 20, 2026

   During their formative stages, giant planets are fed by infalling material sourced from the background circumstellar disk. Due to conservation of angular momentum, the incoming gas and dust collects into a circumplanetary disk that processes the material before it reaches the central planet itself. This work investigates the complex vertical structure of these circumplanetary disks and calculates their radiative signatures. A self-consistent numerical model of the temperature and density structure of the circumplanetary environment reveals that circumplanetary disks are thick and hot, with aspect ratios H/R∼0.1−0.25 and temperatures approaching that of the central planet. The disk geometry has a significant impact on the radiative signatures, allowing future observations to determine critical system parameters. The resulting disks are gravitationally stable and viscosity is sufficient to drive the necessary disk accretion. However, sufficiently rapid mass accretion can trigger a thermal instability, which sets an upper limit on the mass accretion rate. This paper shows how the radiative signatures depend on the properties of the planetary system and discuss how the system parameters can be constrained by future observations.

2. Potential Thermal Profiles of the Third Interstellar Object 3I/ATLAS

   Atsuhiro Yaginuma, Aster G. Taylor, and Darryl Z. Seligman

   MNRAS, Mar 2026

   Abs ADS arXiv

   3 citations

   Updated Apr 20, 2026

   We investigate the thermal evolution of 3I/ATLAS, the third macroscopic interstellar object discovered on 2025 July 1. By comparing modeled thermal profiles with observations of volatile activity, it is possible to constrain bulk physical properties of a cometary nucleus. 3I/ATLAS is actively producing a variety of cometary volatiles. In this paper, we calculate one-dimensional thermal profiles of the third interstellar object 3I/ATLAS throughout its trajectory in an attempt to gain insight into its bulk properties based on measurements of its volatiles. Assuming a variety of typical comet and asteroid bulk geophysical properties such as heat capacities, densities, and conductivities, we calculate the radial thermal profile as a function of depth throughout the hyperbolic trajectory. The methods and code to generate the thermal profile are flexible for any hyperbolic or bound orbit. The thermal profiles are benchmarked to the nominal sublimation temperatures of H2O, CO2 and CO, but are still applicable to any volatile. Comparison between the modeled surface temperatures and the observed onset of H2O activity near 3 au indicates that surface temperatures exceeding ∼150 K can only be achieved if the albedo is below 0.2. We therefore set the upper limit on the albedo of 3I/ATLAS to be 0.2.

2025

1. Onset of CN Emission in 3I/ATLAS: Evidence for Strong Carbon-chain Depletion

   Luis E. Salazar Manzano, Hsing Wen Lin, Aster G. Taylor, and 6 more authors

   The Astrophysical Journal Letters, Nov 2025

   Abs ADS arXiv

   25 citations

   Updated Apr 20, 2026

   Interstellar objects provide a direct window into the environmental conditions around stars other than the Sun. The recent discovery of 3I/ATLAS, a new interstellar comet, offers a unique opportunity to investigate the physical and chemical properties of interstellar objects and to compare them with those of comets in our own Solar System. In this Letter we present the results of a 10-night spectroscopic and photometric monitoring campaign with the 2.4 m Hiltner and 1.3 m McGraw-Hill telescopes at the MDM Observatory. The campaign was conducted between August 8 and 17 while 3I/ATLAS was inbound at heliocentric distances of 3.2 - 2.9 au. Our observations captured the onset of optical gas activity. Nightly spectra reveal a weak CN emission feature in the coma of 3I/ATLAS, absent during the first nights but steadily strengthening thereafter. We measure a CN production rate of Q(CN)∼6×1024 s−1, towards the lower end of activity observed in Solar System comets. Simultaneous photometry also indicates a small but measurable increase in the coma’s radial profile and increasing r-band Afρ with values in the order of ∼300 cm. We derived a gas-to-dust production ratio of logQ(CN)/Afρ∼22.4. Our upper limit on the C2-to-CN ratio (logQ(C2)/Q(CN)≲−0.8) indicates that 3I/ATLAS is a strongly carbon-chain depleted comet. Further observations of 3I/ATLAS are required to verify the apparent carbon-chain depletion and to explore whether such composition represents a recurring trait of the interstellar comet population.

2. The Feasibility of a Spacecraft Flyby with the Third Interstellar Object 3I/ATLAS from Earth or Mars

   Atsuhiro Yaginuma, Tessa Frincke, Darryl Z. Seligman, and 5 more authors

   The Astrophysical Journal, Dec 2025

   Abs ADS arXiv

   10 citations

   Updated Apr 20, 2026

   We investigate the feasibility of a spacecraft mission to conduct a flyby of 3I/ATLAS, the third macroscopic interstellar object discovered on July 1 2025, as it traverses the Solar System. There are both ready-to-launch spacecraft currently in storage on Earth, such as Janus, and spacecraft nearing the end of their missions at Mars. We calculate minimum ΔV single-impulse direct transfer trajectories to 3I/ATLAS both from Earth and from Mars. We consider launch dates spanning January 2025 through March 2026 to explore obtainable and hypothetical mission scenarios. Post-discovery Earth departures require a challenging ΔV≳24 km/s to fly by 3I/ATLAS. By contrast, Mars departures from July 2025 - September 2025 require ΔV∼5 km/s to achieve an early October flyby – which is more feasible with existing propulsion capabilities. We further calculate the phase angle and flyby velocity for these trajectories, noting that the resulting flyby speeds would impose significant observational and engineering challenges that a mission would need to overcome. We discuss how existing spacecraft could be used to observe 3I/ATLAS and how spacecraft at other locations in the Solar System could be repurposed to visit future interstellar objects on short notice.

3. Theoretical Mass Function for Secondaries Forming via Gravitational Instability in Circumstellar Disks

   Fred C. Adams, Aster G. Taylor, and Michael R. Meyer

   Publications of the Astronomical Society of the Pacific, Aug 2025

   Abs ADS arXiv

   3 citations

   Updated Apr 20, 2026

   This paper constructs a theoretical framework for calculating the distribution of masses for secondary bodies forming via gravitational instability in the outer regions of circumstellar disks. We show that several alternate ways to specify the mass scale of forming objects converge to the same result under the constraint that the parental disks are marginally stable with stability parameter Q=1. Next we show that the well-known constraint that the formation of secondary bodies requires rapid cooling is equivalent to that of opacity limited fragmentation. These results are then used to derive a mass function for secondary objects forming through disk instablity. The resulting distribution is relatively narrow, with log-normal-like shape, a characteristic mass scale of order MP∼10 MJup and an approximate range of 4−80 MJup. Current estimates for the occurrence rate suggest that these objects are outnumbered by both stars and planets formed via core accretion.

4. The Kinematic Age of 3I/ATLAS and Its Implications for Early Planet Formation

   Aster G. Taylor, and Darryl Z. Seligman

   The Astrophysical Journal Letters, Sep 2025

   Abs ADS arXiv

   36 citations

   Updated Apr 20, 2026

   The recent discovery of the third interstellar object (3I/ATLAS) expands the known census from two 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 distribution 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.

5. Discovery and Preliminary Characterization of a Third Interstellar Object: 3I/ATLAS

   Darryl Z. Seligman, Marco Micheli, Davide Farnocchia, and 44 more authors

   The Astrophysical Journal Letters, Aug 2025

   Abs ADS arXiv

   91 citations

   Updated Apr 20, 2026

   We report initial observations aimed at the characterization of a third interstellar object candidate. This object, 3I/ATLAS or C/2025 N1 (ATLAS), was discovered on 2025 July 1 UT and has an orbital eccentricity of e∼6.1, perihelion of q∼1.36 au, inclination of ∼175∘, and hyperbolic velocity of V∞∼58 km s−1. We report deep stacked images obtained using the Canada-France-Hawaii Telescope and the Very Large Telescope that resolve a compact coma. Using images obtained from several smaller ground-based telescopes, we find minimal light curve variation for the object over a ∼4 day time span. The visible/near-infrared spectral slope of the object is 17.1±0.2 %/100 nm, comparable to other interstellar objects and primitive solar system small bodies (comets and D-type asteroids), although this result is likely affected by some coma contamination. 3I/ATLAS will be observable through early September 2025, then unobservable by Earth-based observatories near perihelion due to low solar elongation. It will be observable again from the ground in late November 2025. Although this limitation unfortunately prohibits detailed Earth-based observations at perihelion when the activity of 3I/ATLAS is likely to peak, spacecraft at Mars could be used to make valuable observations at this time. Additional photometric, spectroscopic, and polarimetric monitoring of 3I/ATLAS by ground- and space-based telescopes, and possibly spacecraft based at Mars, are highly encouraged for characterizing 3I/ATLAS’s rotational light curve, activity evolution, nongravitational acceleration, and compositional indicators of formation conditions.

2024

1. Two Distinct Populations of Dark Comets Delineated by Orbits and Sizes

   Darryl Z. Seligman, Davide Farnocchia, Marco Micheli, and 7 more authors

   Proceedings of the National Academy of Sciences, Aug 2024

   Abs ADS arXiv

   13 citations

   Updated Apr 20, 2026

   Dark comets are small bodies with no detected coma that have significant nongravitational accelerations explainable by outgassing of volatiles, analogous to the first interstellar object 1I/’Oumuamua. These objects represent a potentially widespread class of small bodies that further populate the continuum between asteroids and comets and for which the active nature is inferred from their orbital motion. We report detections of seven dark comets which demonstrate that there are two distinct populations based on their orbits and sizes. These objects represent a class of Solar System objects that may have delivered material to the Earth necessary for the development of life such as volatiles and organics. Small bodies are capable of delivering essential prerequisites for the development of life, such as volatiles and organics, to the terrestrial planets. For example, empirical evidence suggests that water was delivered to the Earth by hydrated planetesimals from distant regions of the Solar System. Recently, several morphologically inactive near-Earth objects were reported to experience significant nongravitational accelerations inconsistent with radiation-based effects, and possibly explained by volatile-driven outgassing. However, these “dark comets” display no evidence of comae in archival images, which are the defining feature of cometary activity. Here, we report detections of nongravitational accelerations on seven additional objects classified as inactive (doubling the population) that could also be explainable by asymmetric mass loss. A detailed search of archival survey and targeted data rendered no detection of dust activity in any of these objects in individual or stacked images. We calculate dust production limits of ∼10, 0.1, and 0.1 kg s−1 for 1998 FR11, 2001 ME1, and 2003 RM with these data, indicating little or no dust surrounding the objects during the observations. This set of dark comets reveals the delineation between two distinct populations: larger, “outer” dark comets on eccentric orbits that are end members of a continuum in activity level of comets, and smaller, “inner” dark comets on near-circular orbits that could signify a different different population. These objects may trace various stages in the life cycle of a previously undetected, but potentially numerous, volatile-rich population that may have provided essential material to the Earth.

2. Strong Nongravitational Accelerations and the Potential for Misidentification of Near-Earth Objects

   Aster G. Taylor, Darryl Z. Seligman, Matthew J. Holman, and 5 more authors

   The Astrophysical Journal, Nov 2024

   Abs ADS arXiv

   3 citations

   Updated Apr 20, 2026

   Nongravitational accelerations in the absence of observed activity have recently been identified on near-Earth objects (NEOs), opening the question of the prevalence of anisotropic mass loss in the near-Earth environment. Motivated by the necessity of nongravitational accelerations to identify 2010 VL65 and 2021 UA12 as a single object, we investigate the problem of linking separate apparitions in the presence of nongravitational perturbations. We find that nongravitational accelerations on the order of 1 × 10–9 au day−2 can lead to a change in plane-of-sky positions of ∼1 × 103 arcsec between apparitions. Moreover, we inject synthetic tracklets of hypothetical nongravitationally accelerating NEOs into the Minor Planet Center orbit identification algorithms. We find that at large nongravitational accelerations (∣A i ∣ ≥ 1 × 10−8 au day−2) these algorithms fail to link a significant fraction of these tracklets. We further show that if orbits can be determined for both apparitions, the tracklets will be linked regardless of nongravitational accelerations, although they may be linked to multiple objects. In order to aid in the identification and linkage of nongravitationally accelerating objects, we propose and test a new methodology to search for unlinked pairs. When applied to the current census of NEOs, we recover the previously identified case but identify no new linkages. We conclude that current linking algorithms are generally robust to nongravitational accelerations, but objects with large nongravitational accelerations may potentially be missed. While current algorithms are well-positioned for the anticipated increase in the census population from future survey missions, it may be possible to find objects with large nongravitational accelerations hidden in isolated tracklet pairs.

3. Radiative Signatures of Circumplanetary Disks and Envelopes During the Late Stages of Giant Planet Formation

   Aster G. Taylor, and Fred C. Adams

   Icarus, Nov 2024

   Abs ADS arXiv

   5 citations

   Updated Apr 20, 2026

   During the late stages of giant planet formation, protoplanets are surrounded by a circumplanetary disk and an infalling envelope of gas and dust. For systems with sufficient cooling, material entering the sphere of influence of the planet falls inward and approaches ballistic conditions. Due to conservation of angular momentum, most of the incoming material falls onto the disk rather than directly onto the planet. This paper determines the spectral energy distributions of forming planets in this stage of evolution. Generalizing previous work, we consider a range of possible geometries for the boundary conditions of the infall and determine the two-dimensional structure of the envelope, as well as the surface density of the disk. After specifying the luminosity sources for the planet and disk, we calculate the corresponding radiative signatures for the system, including the emergent spectral energy distributions and emission maps. These results show how the observational appearance of forming planets depend on the input parameters, including the instantaneous mass, mass accretion rate, semimajor axis of the orbit, and the planetary magnetic field strength (which sets the inner boundary condition for the disk). We also consider different choices for the form of the opacity law and attenuation due to the background circumstellar disk. Although observing forming planets will be challenging, these results show how the observational signatures depend on the underlying properties of the planet/disk/envelope system.

4. The Dynamical Origins of the Dark Comets and a Proposed Evolutionary Track

   Aster G. Taylor, Jordan K. Steckloff, Darryl Z. Seligman, and 5 more authors

   Icarus, Jul 2024

   Abs ADS arXiv

   9 citations

   Updated Apr 20, 2026

   So-called ‘dark comets’ are small, morphologically inactive near-Earth objects (NEOs) that exhibit nongravitational accelerations inconsistent with radiative effects. These objects exhibit short rotational periods (minutes to hours), where measured. We find that the strengths required to prevent catastrophic disintegration are consistent with those measured in cometary nuclei and expected in rubble pile objects. We hypothesize that these dark comets are the end result of a rotational fragmentation cascade, which is consistent with their measured physical properties. We calculate the predicted size-frequency distribution for objects evolving under this model. Using dynamical simulations, we further demonstrate that the majority of these bodies originated from the ν6 resonance, implying the existence of volatiles in the current inner main belt. Moreover, one of the dark comets, (523599) 2003 RM, likely originated from the outer main belt, although a JFC origin is also plausible. These results provide strong evidence that volatiles from a reservoir in the inner main belt are present in the near-Earth environment.

5. Formation and Structure of Circumplanetary Disks and Envelopes During the Late Stages of Giant Planet Formation

   Aster G. Taylor, and Fred C. Adams

   Icarus, Jun 2024

   Abs ADS arXiv

   8 citations

   Updated Apr 20, 2026

   Giant planets are expected to form within circumplanetary disks, which shape their formation history and the local environment. Here, we consider the formation and structure of circumplanetary disks that arise during the late stages of giant planet formation. During this phase, when most of the final mass is accumulated, incoming material enters the Hill sphere and falls toward the planet. In the absence of torques, the falling parcels of gas conserve their specific angular momentum and collect into a circumplanetary disk. Generalizing previous work, we consider a range of possible geometries for the flow entering the sphere of influence of the planet. Specifically, we consider five geometric patterns for the inward flow, ranging from concentration toward the rotational poles of the system to isotropic flow to concentration along the equatorial plane. For each case, we derive analytic descriptions for the density field of the infall region, the disk surface density in the absence of viscosity, and steady-state solutions for viscous disks. These results, in turn, specify the luminosity contributions of the planet, the circumplanetary disk, and the envelope. These power sources, in conjunction with the surrounding material, collectively determine the observational appearance of the forming planet. We conclude with an approximate determination of these radiative signatures.

6. Potential Melting of Extrasolar Planets by Tidal Dissipation

   Darryl Z. Seligman, Adina D. Feinstein, Dong Lai, and 6 more authors

   Astrophysical Journal, Jan 2024

   Abs ADS arXiv

   37 citations

   Updated Apr 20, 2026

   Tidal heating on Io due to its finite eccentricity was predicted to drive surface volcanic activity, which was subsequently confirmed by the Voyager spacecraft. Although the volcanic activity in Io is more complex, in theory volcanism can be driven by runaway melting in which the tidal heating increases as the mantle thickness decreases. We show that this runaway melting mechanism is generic for a composite planetary body with liquid core and solid mantle, provided that (i) the mantle rigidity, μ, is comparable to the central pressure, i.e., μ/(ρ gR P) ≳ 0.1 for a body with density ρ, surface gravitational acceleration g, and radius R P; (ii) the surface is not molten; (iii) tides deposit sufficient energy; and (iv) the planet has nonzero eccentricity. We calculate the approximate liquid core radius as a function of μ/(ρ gR P), and find that more than 90% of the core will melt due to this runaway for μ/(ρ gR P) ≳ 1. From all currently confirmed exoplanets, we find that the terrestrial planets in the L 98-59 system are the most promising candidates for sustaining active volcanism. However, uncertainties regarding the quality factors and the details of tidal heating and cooling mechanisms prohibit definitive claims of volcanism on any of these planets. We generate synthetic transmission spectra of these planets assuming Venus-like atmospheric compositions with an additional 5%, 50%, and 98% SO2 component, which is a tracer of volcanic activity. We find a ≳3σ preference for a model with SO2 with 5–10 transits with JWST for L 98-59bcd.

7. Seasonally Varying Outgassing as an Explanation for Dark Comet Accelerations

   Aster G. Taylor, Davide Farnocchia, David Vokrouhlický, and 3 more authors

   Icarus, Jan 2024

   Abs ADS arXiv

   5 citations

   Updated Apr 20, 2026

   Significant nonradial, nongravitational accelerations with magnitudes incompatible with radiation-driven effects have been reported in seven photometrically inactive near-Earth objects. Two of these objects exhibit large transverse accelerations (i.e., within the orbital plane but orthogonal to the radial direction), and six exhibit significant out-of-plane accelerations. Here, we find that anisotropic outgassing resulting from differential heating on a nucleus with nonzero spin-pole obliquity, averaged over an eccentric orbit, can explain these accelerations for most of the objects. This balanced outgassing model depends on three parameters — the spin pole orientation (R.A. and Dec.) and an acceleration magnitude. For these “dark comets” (excepting 2003 RM), we obtain parameter values that reproduce the observed nongravitational accelerations. We derive formulae for the component accelerations under certain assumptions for the acceleration scaling over heliocentric distance. Although we lack estimates of these objects’ spin axes to confirm our values, this mechanism is nevertheless a plausible explanation for the observed accelerations, and produces accurate perturbations to the heliocentric motions of most of these objects. This model may also be applied to active objects outside of the dark comets group.

2023

1. Fitting the Light Curve of 1I/’Oumuamua with a Nonprincipal Axis Rotational Model and Outgassing Torques

   Aster G. Taylor, Darryl Z. Seligman, Olivier R. Hainaut, and 1 more author

   Planetary Science Journal, Oct 2023

   Abs ADS arXiv

   4 citations

   Updated Apr 20, 2026

   In this paper, we investigate the nonprincipal axis (NPA) rotational state of 1I/‘Oumuamua—the first interstellar object discovered traversing the inner solar system—from its photometric light curve. Building upon Mashchenko, we develop a model which incorporates NPA rotation and Sun-induced, time-varying outgassing torques to generate synthetic light curves of the object. The model neglects tidal forces, which are negligible compared to outgassing torques over the distances at which ‘Oumuamua was observed. We implement an optimization scheme that incorporates the NPA rotation model to calculate the initial rotation state of the object. We find that an NPA rotation state with an average period of 〈P〉 ≃ 7.34 hr best reproduces the photometric data. The discrepancy between this period and previous estimates is due to continuous period modulation induced by outgassing torques in the rotational model, as well as different periods being used. The best fit to the 2017 October data does not reproduce the 2017 November data (although the later measurements are too sparse to fit). The light curve is consistent with there being no secular evolution of the angular momentum, which is somewhat in tension with the empirical correlations between nuclear spin-up and cometary outgassing. The complex rotation of ‘Oumuamua may be the result of primordial rotation about the smallest principal axis if (i) the object experienced hypervolatile outgassing and (ii) our idealized outgassing model is accurate.

2. Interstellar Comets from Post–Main Sequence Systems as Tracers of Extrasolar Oort Clouds

   W. Garrett Levine, Aster G. Taylor, Darryl Z. Seligman, and 4 more authors

   Planetary Science Journal, Jul 2023

   Abs ADS arXiv

   12 citations

   Updated Apr 20, 2026

   Interstellar small bodies are unique probes into the histories of exoplanetary systems. One hypothesized class of interlopers are "Jurads," exocomets released into the Milky Way during the post-main-sequence as the thermally pulsing asymptotic giant branch (AGB) host stars lose mass. In this study, we assess the prospects for the Legacy Survey of Space and Time (LSST) to detect a Jurad and examine whether such an interloper would be observationally distinguishable from exocomets ejected during the (pre-)main-sequence. Using analytic and numerical methods, we estimate the fraction of exo-Oort Cloud objects that are released from 1-8 M ⊙ stars during post-main-sequence evolution. We quantify the extent to which small bodies are altered by the increased luminosity and stellar outflows during the AGB, finding that some Jurads may lack hypervolatiles and that stellar winds could deposit dust that covers the entire exocomet surface. Next, we construct models of the interstellar small body reservoir for various size-frequency distributions and examine the LSST’s ability to detect members of those hypothesized populations. Combining these analyses, we highlight the joint constraints that the LSST will place on power-law size-frequency distribution slopes, characteristic sizes, and the total mass sequestered in the minor planets of exo-Oort Clouds. Even with the LSST’s increased search volume compared to contemporary surveys, we find that detecting a Jurad is unlikely but not infeasible given the current understanding of (exo)planet formation.

3. Numerical Simulations of Tidal Deformation and Resulting Light Curves of Small Bodies: Material Constraints of 99942 Apophis and 1I/’Oumuamua

   Aster G. Taylor, Darryl Z. Seligman, Douglas R. MacAyeal, and 2 more authors

   Planetary Science Journal, May 2023

   Abs ADS arXiv

   9 citations

   Updated Apr 20, 2026

   In this paper, we present an open-source software (Simulator of Asteroid Malformation Under Stress, SAMUS) that simulates constant-density, constant-viscosity liquid bodies subject to tidal forces for a range of assumed viscosities and sizes. This software solves the Navier-Stokes equations on a finite-element mesh, incorporating the centrifugal, Coriolis, self-gravitational, and tidal forces. The primary functionality is to simulate the deformation of minor bodies under the influence of tidal forces. It may therefore be used to constrain the composition and physical structure of bodies experiencing significant tidal forces, such as 99942 Apophis and 1I/’Oumuamua. We demonstrate that SAMUS will be useful to constrain the material properties of Apophis during its near-Earth flyby in 2029. Depending on the material properties, Apophis may experience an area change of up to 0.5%, with similar effects on the photometric brightness. We also apply SAMUS to constrain the material dynamic viscosity of 1I/’Oumuamua, the first interstellar object discovered traversing the inner solar system. ’Oumuamua experienced a close approach to the Sun at perihelion (q ≃ 0.25 au) during which there were significant tidal forces that may have caused deformation of the body. This deformation could have lead to observable changes in the photometric light curve based on the material properties. The application of SAMUS to produce synthetic observations which incorporate tidal deformation effects demonstrates that no deformation-an infinite dynamic viscosity-best reproduces the photometric data. While these results indicate that ’Oumuamua did not experience significant tidal deformation, a sophisticated model incorporating nonprincipal axis rotation is necessary to conclusively analyze both ’Oumuamua and Apophis.

4. Dark Comets? Unexpectedly Large Nongravitational Accelerations on a Sample of Small Asteroids

   Darryl Z. Seligman, Davide Farnocchia, Marco Micheli, and 15 more authors

   Planetary Science Journal, Feb 2023

   Abs ADS arXiv

   40 citations

   Updated Apr 20, 2026

   We report statistically significant detections of nonradial, nongravitational accelerations based on astrometric data in the photometrically inactive objects 1998 KY26, 2005 VL1, 2016 NJ33, 2010 VL65, 2016 RH120, and 2010 RF12. The magnitudes of the nongravitational accelerations are greater than those typically induced by the Yarkovsky effect, and there is no radiation-based, nonradial effect that can be so large. Therefore, we hypothesize that the accelerations are driven by outgassing and calculate implied H2O production rates for each object. We attempt to reconcile outgassing-induced acceleration with the lack of visible comae or photometric activity via the absence of surface dust and low levels of gas production. Although these objects are small, and some are rapidly rotating, the surface cohesive forces are stronger than the rotational forces, and rapid rotation alone cannot explain the lack of surface debris. It is possible that surface dust was removed previously, perhaps via outgassing activity that increased the rotation rates to their present-day value. We calculate dust production rates of order  10-4 g s-1 in each object, assuming that the nuclei are bare, within the upper limits of dust production from a sample stacked image of 1998 KY26 of M˙Dust<0.2 g s-1. This production corresponds to brightness variations of order  0.0025%, which are undetectable in extant photometric data. We assess the future observability of each of these targets and find that the orbit of 1998 KY26-which is also the target of the extended Hayabusa2 mission-exhibits favorable viewing geometry before 2025.