Research papers 1I/'Oumuamua as an N2 ice fragment of an exo‐Pluto surface I: Size and Compositional Constraints, Alan P. Jackson and Steven J. Desch
and 1I/'Oumuamua as an N2 ice fragment of an exo‐Pluto surface II: Generation of N2 ice fragments and the origin of 'Oumuamua, Steven J, Desch and Alan P. Jackson,
published in Journal of Geophysical Research: Planets, March 2021
Image credit: Painting by William K. Hartmann, based on commission from Michael Belton
Research paper Ejection of rocky and icy material from binary star systems: Implications for the origin and composition of 1I/'Oumuamua, authors Alan P. Jackson, Daniel Tamayo, Noah Hammond, Mohamad Ali-Dib, Hanno Rein
Discovered on 19th October 2017 by the Pan-STARRS 1 telescope at Haleakala Observatory in Hawai'i, 'Oumuamua is an intriguing object. With an eccentricity of 1.2 and travelling at around 26 km/s relative to the Solar system it is the first confirmed body of interstellar origin to pass through the Solar system. In addition it is highly elongated, as can be seen in the artist's impression, and has displayed no detectable coma or tail-like activity, despite having passed within 0.25 AU of the Sun (within the orbit of Mercury), making it a volatile-poor asteroid rather than an ice-rich comet. It was this latter point that particularly interested me and my colleagues at the University of Toronto.
The overwhelming majority of objects that are ejected from our own Solar system out into interstellar space are icy comets that originate from the outer regions like the Kuiper belt, not the inner parts of the Solar system where rocky asteroids are found. This is because the dominant contributors to ejecting material from the Solar system are Neptune and Jupiter, which are themselves in those outer regions. To be more efficient at ejecting material from the warm, inner regions we need a system with a different architecture to ours, one that has a large body in the inner regions. A Jupiter like planet in the inner parts of the system would work, but planet surveys have told us that Jupiter-like planets close to their parent stars are not very common. Binary stars on the other hand are common, with something like half of all stars being members of a binary or multiple star system. Moreover the companion star is there right from the very beginning of the life of the system, so material can start being ejected as soon as planetesimals form, rather than having to wait until a large planet can be formed. As such we found that material ejected from binary stars should dominate the population of interstellar bodies, especially for rocky ones like 'Oumuamua, which then means that 'Oumuamua most likely was born in a binary star system.
Further work later in 2018 by Micheli et al. showed that matching the trajectory of 'Oumuamua through the solar system required a comet-like non-gravitational acceleration, suggesting that 'Oumuamua might actually be a comet rather than a volatile-poor asteroid. See our more recent press release above for a more up-to-date hypothesis for this interesting object.
Image credit: ESO/M. Kornmesser, artist's impression of 1I/'Oumuamua
Image Credit: ESO/M. Kornmesser, artists impression of 1I/'Oumuamua