Přednášky a semináře

Abstract: A population of small main-belt asteroid pairs residing on very similar heliocentric orbits has been found and studied recently (Vokrouhlický and Nesvorný, Astron. J. 136, 280, 2008; Pravec and Vokrouhlický, Icarus 204, 580, 2009; Vokrouhlický, Astron. J. 137, 111 2009). These asteroid pairs show some common properties: they are ubiquitous with pairs found throughout the asteroid population, pair members are separated with low relative velocities (as low as 0.17~m/s), they are young with most pairs separated less than 1 Myr ago, and their sizes and mass ratios overlap with the population of orbiting, bound binary systems. Previous investigations of binary asteroids suggest that they were formed from parent bodies spinning at a critical rate by some sort of fission or mass shedding process (Pravec and Harris, Icarus 190, 250, 2007; Scheeres, Icarus 189, 370, 2007; Walsh et al., Nature 454, 188, 2008), however the possibility that these two populations of asteroid pairs and binaries were related was intriguing but lacked of bservational data. In our recent paper (Pravec et al., Nature 466, 1085, 2010), we reported on a systematic observation campaign of spin rates, relative sizes and shapes of paired asteroids which enables this population to be analyzed. Two key characteristics of the asteroid pairs population appear: the primary spin rate is correlated with the mass ratio between a pair's components, and there is a cut-off in mass ratios of asteroid pairs above a value of 0.2. Both of these results are predicted by the rotational fission process hypothesized in Scheeres (Icarus 189, 370, 2007), and suggests this or a similar process as the genesis of the asteroid pairs and by implication as a fundamental process in the formation of asteroid binary systems. This formation mechanism is distinct from previous hypotheses to explain the population of orbiting, bound binary asteroid systems (Walsh et al., Nature 454, 188, 2008).