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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.

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 thatSAMUSwill 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 applySAMUSto 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 ofSAMUSto 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.

We report a statistically significant detection of nongravitational acceleration on the subkilometer near-Earth asteroid (523599) 2003 RM. Due to its orbit, 2003 RM experiences favorable observing apparitions every 5 yr. Thus, since its discovery, 2003 RM has been extensively tracked with ground-based optical facilities in 2003, 2008, 2013, and 2018. We find that the observed plane-of-sky positions cannot be explained with a purely gravity-driven trajectory. Including a transverse nongravitational acceleration allows us to match all observational data, but its magnitude is inconsistent with perturbations typical of asteroids such as the Yarkovsky effect or solar radiation pressure. After ruling out that the orbital deviations are due to a close approach or collision with another asteroid, we hypothesize that this anomalous acceleration is caused by unseen cometary outgassing. A detailed search for evidence of cometary activity with archival and deep observations from the Panoramic Survey Telescope and Rapid Response System and the Very Large Telescope does not reveal any detectable dust production. However, the best-fitting H₂O sublimation model allows for brightening due to activity consistent with the scatter of the data. We estimate the production rate required for H₂O outgassing to power the acceleration and find that, assuming a diameter of 300 m, 2003 RM would require Q(H₂O) ∼ 10²³molec s⁻¹at perihelion. We investigate the recent dynamical history of 2003 RM and find that the object most likely originated in the mid-to-outer main belt (∼86% probability) as opposed to from the Jupiter-family comet region (∼11% probability). Further observations, especially in the infrared, could shed light on the nature of this anomalous acceleration.

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 ∼10⁻⁴g s⁻¹in each object, assuming that the nuclei are bare, within the upper limits of dust production from a sample stacked image of 1998 KY₂₆of${\dot{M}}_{\mathrm{Dust}}<0.2$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.

Manx comets are objects on long-period comet orbits that are inactive as they approach perihelion. They are of particular interest because they may help constrain solar system formation models. 2013 LU28 was discovered as an inactive asteroidal object on 2013 June 8 at a heliocentric distance of 21.8 au. Images and photometric data were obtained of 2013 LU28 from multiple telescopes from pre-discovery data in 2010 until the present. Its spectral reflectivity is consistent with typical organic-rich comet surfaces with colors of$g\prime -r\prime$= 0.97 ± 0.02,$r\prime -i\prime$= 0.43 ± 0.02, and$r\prime -z\prime$= 0.65 ± 0.03, corresponding to a spectral reflectivity slope of 30 ± 3%/100 nm. There is no obvious indication of dust coma in deep stacked images. We estimate the nucleus radius to be ∼55.7 ± 0.3 km assuming an albedo of 4%. This is much smaller than the 1σupper limits on the nucleus size of 79.9 km from the NEOWISE survey assuming the same albedo, since the NEOWISE survey is not very sensitive to objects this small at this distance. The heliocentric light curve suggests possible activity betweenr∼ 17 and 13 au where 2013 LU28 is brighter than expected. This is consistent with outgassing from CO or CO₂. Using surface brightness profiles, we estimate an upper limit of ∼0.01 kg s⁻¹for micron-sized dust that can be produced without us detecting it for the inactive portion of the light curve, and upper limits of ∼1 kg s⁻¹for CO and ∼1.5 kg s⁻¹for CO₂between 20 and 14.7 au.

Manx objects approach the inner solar system on long-period comet (LPC) orbits with the consequent high inbound velocities, but unlike comets, Manxes display very little to no activity even near perihelion. This suggests that they may have formed in circumstances different from typical LPCs; moreover, this lack of significant activity also renders them difficult to detect at large distances. Thus, analyzing their physical properties can help constrain models of solar system formation as well as sharpen detection methods for those classified as NEOs. Here, we focus on the Manx candidate A/2018 V3 as part of a larger effort to characterize Manxes as a whole. This particular object was observed to be inactive even at its perihelion atq= 1.34 au in 2019 September. Its spectral reflectivity is consistent with typical organic-rich comet surfaces with colors of$g\prime -r\prime =0.67\pm 0.02$,$r\prime -i\prime =0.26\pm 0.02$, and$r\prime -z\prime =0.45\pm 0.02$, corresponding to a spectral reflectivity slope of 10.6 ± 0.9%/100 nm. A least-squares fit of our constructed light curve to the observational data yields an average nucleus radius of ≈2 km assuming an albedo of 0.04. This is consistent with the value measured from NEOWISE. A surface brightness analysis for data taken 2020 July 13 indicated possible low activity (≲0.68 g s⁻¹), but not enough to lift optically significant amounts of dust. Finally, we discuss Manxes as a constraint on solar system dynamical models as well as their implications for planetary defense.