Spin Change of Asteroid 2012 TC4 Probably by Radiation Torques

Abstract

Asteroid 2012 TC4 is a small (∼10 m) near-Earth object that was observed during its Earth close approaches in 2012 and 2017. Earlier analyses of light curves revealed its excited rotation state. We collected all available photometric data from the two apparitions to reconstruct its rotation state and convex shape model. We show that light curves from 2012 and 2017 cannot be fitted with a single set of model parameters; the rotation and precession periods are significantly different for these two data sets, and they must have changed between or during the two apparitions. Nevertheless, we could fit all light curves with a dynamically self-consistent model assuming that the spin states of 2012 TC4 in 2012 and 2017 were different. To interpret our results, we developed a numerical model of its spin evolution in which we included two potentially relevant perturbations: (i) gravitational torque due to the Sun and Earth and (ii) radiation torque, known as the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. Despite our model simplicity, we found that the role of gravitational torques is negligible. Instead, we argue that the observed change of its spin state may be plausibly explained as a result of the YORP torque. To strengthen this interpretation, we verify that (i) the internal energy dissipation due to material inelasticity and (ii) an impact with a sufficiently large interplanetary particle are both highly unlikely causes of its observed spin state change. If true, this is the first case where the YORP effect has been detected for a tumbling body.

Secular change in the spin states of asteroids due to radiation and gravitation torques

“…In this respect, we note that the detection of the YORP effect for an asteroid in a tumbling state is yet another novelty. An indication of such detection can be found in the analysis of the rotation state of the very small asteroid 2012 TC4 (see Lee et al 2021). The accurately monitored A93, page 18 of 25 Ďurech, J., et al: A&A, 682, A93 (2024) rotation state of (99942) Apophis (e.g.…”

The Asteroid-Comet Continuum

“…Eight asteroids in the published literature display evidence for spin-up, namely (1620) Geographos (which interestingly is also a suspected meteor stream parent; Ryabova 2002, also see Section 2.5), (1862) Apollo, (3103) Eger, (25143) Itokawa, (54509) YORP, and (161989) Cacus, (1685) Toro, and (10115) 1992 SK (Rozitis and Green 2013; Lowry et al 2014;Durech et al 2018Durech et al , 2022. Figure 8 shows characteristic spin-up timescales for these asteroids computed using τ = ω/ ω, where ω is the measured angular frequency, as a function of diameter, where the 10 m scale asteroid 2012 TC 4 shows evidence for multiple periods and spin-up (Lee et al 2021) but is Fig. 8.-Empirical YORP timescales for small asteroids (marked by their numerical designations) as a function of diameter, using published measurements of spin-period changes.…”

Refinement of the convex shape model and tumbling spin state of (99942) Apophis using the 2020–2021 apparition data

“…The optimization for each P φ was performed in the same way as in Lee et al (2020Lee et al ( , 2021. In these procedure, the Hapke's model parameters were set to those of a typical S-type asteroid: = 0.23, g = −0.27, h = 0.08, B 0 = 1.6, /c dyn are the axial ratios of a dynamically equivalent ellipsoid; a shape /c shape and c shape /c shape are the axial ratios of a convex shape model; E/E 0 is the ratio of the rotational kinetic energy to the lowest energy for the given angular momentum.…”