UW Astronomers Observe Interstellar Asteroid

Concept art of 1I/’Oumuamua. Credit: M. Kornmesser/ESO

On October 25, 2017, the first discovery of an interstellar object (ISO), 1I/’Oumuamua, was announced to the world after it was detected by the Pan-STARRS telescope in Maui, Hawaii. Initially, the object was thought to be a comet from the far reaches of the solar system in a region known as the Oort Cloud, where objects have extreme orbits that take them careening through the inner solar system at speeds exceeding 60 km/s, too high to be bound to our solar system. Additional obs

ervations also showed that it was not cometary, but instead appeared more like an asteroid.

Soon after the Minor Planet Center’s official announcement of 1I, a group of astronomers at the University of Washington — Bryce Bolin (also at B612 Asteroid Institute), Lynne Jones, Daniela Huppenkothen, Joachim Moeyens, Mario Jurić, Željko Ivezić and Andrew Connolly — teamed up with researchers Hal Weaver and Carey Lisse at Johns Hopkins University Applied Physics Laboratory and Yan Fernandez from the University of Central Florida, and rapidly obtained observations at the Apache Point 3.5 m telescope in Sunspot, New Mexico.

Sequence of APO observations of 1I/’Oumuamua (click through for animated gif)

The team observed 1I in the New Mexico desert skies, imaging it in three different color filters and obtaining measurements covering a 4-hour lightcurve. The photometric data revealed that 1I had a likely rotation period of ~8.1 hours and an unusually high aspect ratio ~6:1. This aspect ratio revealed that the object is shaped like a fingerling potato. In addition, photometric color measurements implied that 1I has surface similar to primitive C and D type asteroids from the asteroid Main Belt and Jupiter Trojan swarms. These results are in agreement with several independent studies of 1I by groups at the University of Hawaii, University of California, Los Angeles and Queen’s University Belfast. The UW results have been accepted to the Astrophysical Journal Letters (Bolin et al., “APO Time Resolved Color Photometry of Highly-Elongated Interstellar Object 1I/’Oumuamua”), with a preprint available on the arXiv.

A full description of the work by UW astronomers is available on the Dirac website.