Extreme Asteroids in the Pan-STARRS 1 Survey

Abstract

Using the first 18 months of the Pan-STARRS 1 survey, we have identified 33 candidate high-amplitude objects for follow-up observations and carried out observations of 22 asteroids. Four of the observed objects were found to have observed amplitude A obs  ≥ 1.0 mag. We find that these high-amplitude objects are most simply explained by single rubble-pile objects with some density-dependent internal strength, allowing them to resist mass shedding even at their highly elongated shapes. Three further objects, although below the cutoff for “high amplitude,” had a combination of elongation and rotation period which also may require internal cohesive strength, depending on the density of the body. We find that none of the “high-amplitude asteroids” identified here require any unusual cohesive strengths to resist rotational fission. Three asteroids were sufficiently observed to allow for shape and spin-pole models to be determined through light curve inversion. Asteroid 45864 was determined to have retrograde rotation with spin-pole axes λ  = 218° ± 10°, β  = −82° ± 5° and asteroid 206167 was found to have best-fit spin-pole axes λ  = 57° ± 5°, β  = −67° ± 5°. An additional object not initially measured with A obs  > 1.0 mag, 49257, was determined to have a shape model that does suggest a high-amplitude object. Its spin-pole axes were best fit for values λ  = 112°± 6°, β  = 6° ± 5°. In the course of this project, to date no large superfast rotators ( P rot < 2.2 hr) have been identified.