The recent discovery by Pan-STARRS1 of 1I/2017 U1 ( ‘ Oumuamua ) , on an unbound and hyperbolic orbit , offers a rare opportunity to explore the planetary formation processes of other stars , and the effect of the interstellar environment on a planetesimal surface .
1I/ ‘ Oumuamua ’ s close encounter with the inner Solar System in 2017 October was a unique chance to make observations matching those used to characterize the small-body populations of our own Solar System .
We present near-simultaneous g ^ { \prime } , r ^ { \prime } , and J photometry and colors of 1I/ ‘ Oumuamua from the 8.1-m Frederick C. Gillett Gemini North Telescope , and gri photometry from the 4.2 m William Herschel Telescope .
Our g ^ { \prime } r ^ { \prime } J observations are directly comparable to those from the high-precision Colours of the Outer Solar System Origins Survey ( Col-OSSOS ) , which offer unique diagnostic information for distinguishing between outer Solar System surfaces .
The J-band data also provide the highest signal-to-noise measurements made of 1I/ ‘ Oumuamua in the near-infrared .
Substantial , correlated near-infrared and optical variability is present , with the same trend in both near-infrared and optical .
Our observations are consistent with 1I/ ‘ Oumuamua rotating with a double-peaked period of 8.10 \pm 0.42 hours and being a highly elongated body with an axial ratio of at least 5.3:1 , implying that it has significant internal cohesion .
The color of the first interstellar planetesimal is at the neutral end of the range of Solar System g - r and r - J solar-reflectance colors : it is like that of some dynamically excited objects in the Kuiper belt and the less-red Jupiter Trojans .