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

Abstract

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.

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

“…For objects like 3200 Phaethon, tidal deformation may be detectable in photometric data, and would enable more strenuous constraints on the bulk physical properties of those objects. The recent detection of "dark comets" (Chesley et al 2016;Farnocchia et al 2022;Seligman et al 2023) and their still-unknown provenance provides another class of objects which may benefit from the application of SAMUS and other techniques developed in this paper.…”

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

“…The recent discovery of "dark comets" in the solar system (Chesley et al 2016;Farnocchia et al 2023;Seligman et al 2023) -comaless objects with significant non-radial nongravitational accelerations too strong to be explained by non-outgassing effects -provides an excellent opportunity to resolve outstanding questions about the nature of undetected outgassing. Future investigations of these comets with JWST and with the Hayabusa2 extended mission to the "dark comet" 1998 KY26 (Hirabayashi et al 2021) could measure the predicted levels of outgassing and possibly dust.…”

ASTERIA—Asteroid Thermal Inertia Analyzer

“…Along with the A 2 acceleration component, JPL also found an out-of-orbital plane, the A 3 acceleration component. Seligman et al (2023) hypothesized that the A 3 component in small asteroids could be due to nondetected cometary-like activity. Therefore, the same reasoning places the object in the category of "dark comets."…”