Tidal Evolution of Binary Asteroids: Eccentric Mutual Orbits and Contact Binary Formation

Details Tidal Evolution of Binary Asteroids: Eccentric Mutual Orbits and Contact Binary Formation Tidal Evolution of Binary Asteroids: Eccentric Mutual Orbits and Contact Binary Formation

Sep 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008dps....40.5508t&link_type=abstract

American Astronomical Society, DPS meeting #40, #55.08; Bulletin of the American Astronomical Society, Vol. 40, p.499

Astronomy and Astrophysics

Astronomy

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Scientific paper

We will discuss ongoing research on the tidal evolution of binary asteroids, concentrating on explaining the observed asynchronous binaries with eccentric mutual orbits and the production of contact binary asteroids. Eccentric, asynchronous binaries may be explained by having a secondary that is mechanically stronger (in terms of the product of rigidity and tidal dissipation factor uQ) than the primary. This would naturally allow for excitation of the eccentricity by tides and, given an initial spin rate faster than the mean motion at the onset of tidal evolution, prevent the spin of the secondary from synchronizing with the orbital mean motion. Secondaries that are roughly an order of magnitude weaker than the primary in terms of uQ can naturally explain the circularized binaries in the near-Earth region and the main belt. Contact binaries can be obtained with the help of tidal evolution whenever a system of two components lacks a physically plausible, fully despun, synchronous end state. This can occur in (at least) three ways: (i) the system has too little angular momentum for a synchronous end state to exist for the mass ratio of the components, (ii) the system loses angular momentum through YORP spin-down, for instance, until a synchronous orbit does not exist for the system's mass ratio, and (iii) for oblate primaries, certain combinations of mass ratio (typically > 0.8) and angular momentum cannot support a synchronous end state. In each case, tides will work to pull the components together forming contact binaries. Method (i) requires that the components be separated by a binary formation process that also produces slowly rotating components (<< mean motion). All three methods are most efficient for mass ratios > 0.1 such that one would expect to find contact binaries with components of similar size, which we do observe.

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