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Paper: The Asteroid Spin-Rate Study: Looking for Super Fast Rotators in the Outer Main Belt
Volume: 513, Serendipities in the Solar System and Beyond
Page: 93
Authors: Chang, C.-K.; Lin, H.-W.; Ip, W.-H.
Abstract: Super-fast rotators (SFRs) are important to understand asteroid interior structure. Asteroids larger than a few hundred meter and up to tens of kilometers are believed to have rubble piles structure (i.e., gravitationally bounded aggregations; hereafter, rubble-pile asteroids). One of the supportive evidences is the 2-hour spin-barrier (i.e., rotation periods always of > 2 hour) seen among rubble-pile asteroids, which is a result that the exceedingly centrifugal force induced from a super-fast rotation (i.e., a rotation period < 2 hour) would overcome the gravity and break up rubble-pile asteroids. This 2-hour spin-barrier also leads to an upper limit of 3 g cm–3 for the bulk density of asteroid, which is comparable with the measurements obtained from space missions and multiple-body systems. However, SFRs (asteroids in the size range of rubble-pile asteroid have a rotation period of < 2 hour) show contradictories to the aforementioned picture. The internal cohesion was proposed to explain their existence, and a considerable number of sub-kilometer sized SFRs should therefore be expected. To date, only six SFRs were found and, moreover, a taxonomic tendency seems to be presented among them (i.e., none of them are of C-type asteroids). This probably suggests that SFRs is an individual group beside average asteroids. A simple way to test this possible taxonomic tendency is to look for C-type SFRs. Therefore, we conducted a rotation period survey in October 2016 using PS1, which has a limiting magnitude of 22 that can detect sub-kilometer sized asteroids in the outer main belt, a region dominated by C-type asteroids. We preliminarily obtained ∼ 900 reliable rotation periods, from which (a) a spin-rate distributions was constructed that shows number decrease with increasing spin-rate, and (b) several SFR candidates were found. One of the SFR candidates is an outer-main-belt asteroid and we were, however, not able to determine its taxonomic type due to its ambiguous color obtained during the survey. Therefore, a spectroscopic confirmation is needed in the near future.
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