Equatorial cavities on asteroids, an evidence of fission events

• Published in: Icarus (New York, N.Y. 1962) N.Y. 1962), 2018-04, Vol.304, p.192-208
• Main Authors: Tardivel, Simon, Sánchez, Paul, Scheeres, Daniel J.
• Format: Article
• Language: English
• Subjects: Asteroid; Cohesion; Effective gravity; Fission; Structure
• ISSN: 0019-1035; 1090-2643
• DOI: 10.1016/j.icarus.2017.06.037

•The chances of creating equatorial cavities on NEOs through cratering are very low.•Regolith filling the cavities comes in tension at high spin rates and fissions off.•The interface cohesive strength at the moment of fission is between 1 and 10  Pa.•This low strength can be achieved by kinetic sieving of the asteroid regolith.•The deformation during spin-up naturally generates rocky equators and sandy tropics. This paper investigates the equatorial cavities found on asteroids 2008 EV5 and 2000 DP107 Alpha. As the likelihood of these cavities being impact craters is demonstrated to be low, the paper presents a fission mechanism that explains their existence as a scar of past fission events. The dynamical environment of “top-shaped” asteroids is such that, at high spin rates, an identifiable equatorial region enters into tension before the rest of the body. We propose hypothetical past shapes for 2008 EV5 and 2000 DP107, with mass added within the cavity to recreate a smoother equatorial ridge. The dynamical environment of these hypothetical parent bodies reveal that this modified region is indeed set in tension when spin is increased. The fission process requires tensile strength at the interface between the ejecta and the remaining body, at the moment of fission, between 0 and 2  Pa for 2008 EV5 and between 0 and 15  Pa for 2000 DP107, depending on the precise fission scenario considered. Going back to the spin-up deformation phase of the asteroids, the paper examines how kinetic sieving can form predominantly rocky equators, whose tensile strength could be much lower than that of the rest of the body. This process could explain the low cohesion values implied for this fission mechanism.