Temperature history and dynamical evolution of (101955) 1999 RQ 36: A potential target for sample return from a primitive asteroid

Abstract

It has been recently shown that near-Earth objects (NEOs) have a temperature history-due to the radiative heating by the Sun-non-trivially correlated to their present orbits. This is because the perihelion distance of NEOs varies as a consequence of dynamical mechanisms, such as resonances and close encounters with planets. Thus, it is worth investigating the temperature history of NEOs that are potential targets of space missions devoted to return samples of prebiotic organic compounds. Some of these compounds, expected to be found on NEOs of primitive composition, breakup at moderate temperatures, e.g., 300-670 K. Using a model of the orbital evolution of NEOs and thermal models, we studied the temperature history of (101955) 1999 RQ36 (the primary target of the mission OSIRIS-REx, proposed in the program New Frontiers of NASA). Assuming that the same material always lies on the surface (i.e., there is no regolith turnover), our results suggest that the temperatures reached during its past evolution affected the stability of some organic compounds at the surface (e.g., there is 50% probability that the surface of 1999 RQ36 was heated at temperatures ≥500 K). However, the temperature drops rapidly with depth: the regolith at a depth of 3-5 cm, which is not considered difficult to reach with the current designs of sampling devices, has experienced temperatures about 100 K below those at the surface. This is sufficient to protect some subsurface organics from thermal breakup. © 2011. The American Astronomical Society. All rights reserved. Printed in the U.S.A.