Low thermal conductivity of the superfast rotator (499998) 2011 PT

Abstract

Context. Asteroids with a diameter of up to a few dozen meters may spin very fast and complete an entire rotation within a few minutes. These small and fast-rotating bodies are thought to be monolithic objects because the gravitational force due to their small size is not strong enough to counteract the strong centripetal force caused by the fast rotation. This argument means that the rubble-pile structure is not feasible for these objects. Additionally, it is not clear whether the fast spin prevents dust and small particles (regolith) from being kept on their surface. Aims. We develop a model for constraining the thermal conductivity of the surface of the small, fast-rotating near-Earth asteroids. This model may suggest whether regolith is likely present on these objects. Methods. Our approach is based on the comparison of the measured Yarkovsky drift and a predicted value using a theoretical model that depends on the orbital, physical and thermal parameters of the object. The necessary parameters are either deduced from statistical distribution derived for near-Earth asteroids population or determined from observations with associated uncertainty. With this information, we performed Monte Carlo simulations and produced a probability density distribution for the thermal conductivity. Results. Applying our model to the superfast rotator asteroid (499998) 2011 PT, we find that the measured Yarkovsky drift can only be achieved when the thermal conductivity K of the surface is low. The resulting probability density function for the conductivity is bimodal, with two most likely values being around 0.0001 and 0.005 W m−1 K−1. Based on this, we find that the probability that K is lower than 0.1 W m−1 K−1 is at least 95%. This low thermal conductivity might indicate that the surface of 2011 PT is covered with a thermal insulating layer, composed of a regolith-like material similar to lunar dust.

The role of the Yarkovsky effect in the long-term dynamics of asteroid (469219) Kamo'oalewa

“…However, physical characteristics are usually known up to a certain degree, and some of them may be even unknown. For this reason, following Fenucci et al (2021), we modeled the input parameters and used a Monte Carlo approach to predict the most likely values of the semi-major axis drifts given by Eq. (3).…”

“…We follow a probabilistic model of the parameters similar to Fenucci et al (2021), that we briefly describe hereafter.…”

“…Diameter and density. A population-based distribution for the diameter D and the density ρ of a given NEO has been developed in Fenucci et al (2021), and it is based on the NEOs orbital and absolute magnitude distribution model by Granvik et al (2018) and the NEOs albedo distribution by Morbidelli et al (2020). The NEOs orbital distribution model provides the probability for Kamo'oalewa to come from a specific region of the main belt (see Table 2), i.e.…”

“…Note-For the S-complex we used the density of S-type asteroids given in Carry (2012), while for C-and X-complexes we used the same values as Fenucci et al (2021).…”

“…Accurate modeling of the Yarkovsky effect requires knowledge of the physical properties of the object (Vokrouhlický et al 2015), which are mostly still not available. However, the semimajor axis drift induced by the Yarkovsky effect may be successfully estimated using statistical methods, like the one recently developed by Fenucci et al (2021), that we adopted here.…”