`Oumuamua, our Solar System's first interstellar visitor
by
Karen Meech(Institute for Astronomy, UH)
→
Pacific/Honolulu
Description
None of the approximately 750,000 known asteroids and comets is thought to have originated outside our Solar System, but formation models suggest that orbital migration of the giant planets ejected a large fraction of the original planetesimals into interstellar space. The predicted interstellar number density of icy interstellar objects of 2.4 × 10-4 au-3 suggested that these should have been detected by surveys, yet hitherto none had been seen. Many decades of asteroid and comet characterization have yielded formation models that explain the mass distribution, chemical abundances and planetary configuration of today’s Solar System, but until now there has been no way to tell if our Solar System is typical. I will present the discovery, the worldwide observing campaign to characterize 1I/2017 U1 (‘Oumuamua) and what we have learned from this campaign. Our observations reveal the object to be asteroidal, with no hint of cometary activity despite an approach within 0.25 au of the Sun. Spectroscopic measurements show that the object’s surface is consistent with comets or organic-rich asteroid surfaces found in our own Solar System. Light-curve observations indicate that the object has an extreme oblong shape, unlike anything seen in our Solar System. The presence of ‘Oumuamua suggests that previous estimates of the density of interstellar objects were pessimistically low. I will also discuss some of the implications of this discovery.