Spectroscopy and thermal modelling of the first interstellar object 1I/2017 U1 'Oumuamua

Abstract

During the formation and evolution of the Solar System, significant numbers of cometary and asteroidal bodies were ejected into interstellar space${}^{1,2}$. It can be reasonably expected that the same happened for planetary systems other than our own. Detection of such Inter- stellar Objects (ISOs) would allow us to probe the planetesimal formation processes around other stars, possibly together with the effects of long-term exposure to the interstellar medium. 1I/2017 U1 'Oumuamua is the first known ISO, discovered by the Pan-STARRS1 telescope in October 2017${}^3$.The discovery epoch photometry implies a highly elongated body with radii of $\sim 200\times 20$ m when a comet-like geometric albedo of 0.04 is assumed. Here we report spectroscopic characterisation of 'Oumuamua, finding it to be variable with time but similar to organically rich surfaces found in the outer Solar System. The observable ISO population is expected to be dominated by comet-like bodies in agreement with our spectra, yet the reported inactivity implies a lack of surface ice. We show this is consistent with predictions of an insulating mantle produced by long-term cosmic ray exposure. An internal icy composition cannot therefore be ruled out by the lack of activity, even though 'Oumuamua passed within 0.25 au of the Sun.

4 figures, 1 table; Accepted for publication in Nature Astronomy, data are available at https://github.com/asteroidnerd/Oumuamua-spectroscopy

References in corpus (6)

• Interstellar Interloper 1I/2017 U1: Observations from the NOT and WIYN Telescopes
• An Observational Upper Limit on the Interstellar Number Density of Asteroids and Comets
• 1I/2017 U1 (`Oumuamua) is Hot: Imaging, Spectroscopy and Search of Meteor Activity
• On the rotation period and shape of the hyperbolic asteroid 1I/`Oumuamua (2017) U1 from its lightcurve
• Col-OSSOS: z Band Photometry Reveals Three Distinct TNO Surface Types
• The Hubble Wide Field Camera 3 Test of Surfaces in the Outer Solar System: Spectral Variation on Kuiper Belt Objects

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• High-Drag Interstellar Objects And Galactic Dynamical Streams