Observed tidal evolution of Kleopatra’s outer satellite

Vol. 657
11. Celestial mechanics and astrometry

Observed tidal evolution of Kleopatra’s outer satellite

by M. Broz, J. Durech, B. Carry, F. Vachier, F. Marchis, J. Hanus, L. Jorda, P. Vernazza, D. Vokrouhlicky, M. Walterova, and R. Behrend 2022, A&A, 657, A76

(216) Kleopatra is a main belt asteroid, which was discovered in 1880. Is is an interesting body, not only because of its size and its bone shape, but also because it has two satellites. These two moons, named Alexhelios and Cleoselene, have been detected since 2008. Observing their orbits gives important clues on the physical properties of their primary body (216) Kleopatra. In this paper, the authors use a precovery of Alexhelios, dating back to 1980, to constrain the tidal dissipation in the system. Tides are considered to be the major source of dissipation in such a system. It is a weak, long-term effect, which can be responsible for the synchronization of the rotation of moons with their orbits. Constraining them requires accurate observations over a long duration. This 1980 precovery is an occultation of Kleopatra by its outer satellite Alexhelios, which had been serendipitously recorded by two different observers. An analysis of this event shows that the longitude of Alexhelios is shifted by 60° with respect to a prediction by a model which neglects tides. This result permitted the authors to estimate that the dissipation in Kleopatra is stronger than in our Moon, but smaller than in the satellite of Jupiter Io. Moreover, a consistent tidal model leads to predictions on the spin evolution of Kleopatra and the orbit of its inner satellite Cleoselene, which future observations will challenge.