Barrel Instability in Binary Asteroids

Most close-in planetary satellites are in synchronous rotation, which is usually the stable end-point of tidal despinning. Saturn’s moon Hyperion is a notable exception by having a chaotic rotation. Hyperion’s dynamical state is a consequence of its high eccentricity and its highly prolate shape. As many binary asteroids also have elongated secondaries, chaotic rotation is expected for moons in eccentric binaries, and a minority of asteroidal secondaries may be in that state. The question of secondary rotation is also important for the action of the binary Yarkovsky–O’Keefe–Radzievskii–Paddack (BYORP) effect, which can quickly evolve orbits of synchronous (but not nonsynchronous) secondaries. Here we report results of a large set of short numerical simulations which indicate that, apart from synchronous and classic chaotic rotation, close-in irregularly shaped asteroidal secondaries can occupy an additional, intermediate rotational state. In this “barrel instability” the secondary slowly rolls along its long axis, while the longest axis is staying largely aligned with the primary–secondary line. This behavior may be more difficult to detect through lightcurves than a fully chaotic rotation, but would likewise shut down BYORP. We show that the binary’s eccentricity, separation measured in secondary’s radii and the secondary’s shape are all important for determining whether the system settles in synchronous rotation, chaotic tumbling, or barrel instability. We compare our results for synthetic asteroids with known binary pairs to determine which of these behaviors may be present in the near-Earth asteroid binary population.

The solar system data in the forthcoming Data Release 3 by the Gaia mission of ESA: a preview

<p>The Data Release 3 by the Gaia mission (ESA) will not only multiply by a large factor the volume of observations, but will also add more quality and complexity. With respect to DR2, that appeared in 2018. The number of asteroids with astrometry and photometry will be multiplied by a factor >10, and data will span a longer time interval. Also, for the first time a set of reflectance spectra for several thousand asteroids will be released. Some planetary satellites and candidate new asteroids will also be included. The improvement in volume, accuracy and variety of data will add new dimensions to the contribution of Gaia to asteroid science as this will probably be the most extensive and self consistent set of visible spectra available up to know. </p> <p>In this talk, we will mainly focus on the general properties of the asteroid data in DR3 (statistics on the sample) and on the improvement in astrometry with respect to DR2. Based on the results obtained from the exploitation of DR2, we will review the expected impact of DR3 in terms of improved orbits, Yarkovsky determination, prediction of asteroid occultations. The properties of asteroid spectra in DR3 will be presented in another contribution to this meeting by M. Delbo'. </p>

Gravitational instability and the formation of planetary systems of solar-type stars

The fundamental principles of the protoplanetary ring model – the model of formation of planetary systems of stars, which is based on the origin and development of large-scale gravitational instabilities (protoplanetary rings) – are extended to the formation of regular planetary satellites. Based on these principles, a complete model of the formation of planetary systems, including their satellites, (model of gas and dust rings) for solar-type stars is proposed.