Selections from 2019: Explanation for an Interstellar Visitor

Editor’s note: In these last two weeks of 2019, we’ll be looking at a few selections that we haven’t yet discussed on AAS Nova from among the most-downloaded papers published in AAS journals this year. The usual posting schedule will resume in January.

High-drag Interstellar Objects and Galactic Dynamical Streams

Published March 2019

Main takeaway:

Remember the first known interstellar asteroid, 1I/’Oumuamua? A study by scientist Marshall Eubanks (Space Initiatives, Inc.) explores the possibility that the asteroid is a very lightweight, high-drag object that long ago orbited the galaxy, became caught up within dense interstellar gas, and was then released in our direction as part of the Pleiades dynamical stream.

Why it’s interesting:

'Oumuamua velocity

‘Oumuamua’s incoming velocity is consistent with the dynamics of the Pleiades stream. [Eubanks 2019]

This interstellar object visited our solar system for only a brief time, and it displayed a number of perplexing behaviors — like its unexpected acceleration boost as it left the solar system again. Eubanks’ hypothesis provides a plausible natural explanation: if ‘Oumuamua is a body with a large area-to-mass ratio, solar radiation pressure could have provided the acceleration boost (note that this is the same explanation used by Bialy & Loeb to argue that ‘Oumuamua could be a light sail). And this same lightweight, high-drag structure makes it easy for the asteroid to have become entrained in interstellar gas before being sent into our solar system with the Pleiades stream.

Why This Could Provide Cool Future Opportunities:

In Eubanks’ model, ‘Oumuamua may not be unique. Instead, this object could be just one of an entire population of light asteroids with large area-to-mass ratios — all of which are likely to be entrained with dense gas and could be ejected toward us in streams. By searching stellar streams for bodies like this one, we could identify future interstellar visitors like ‘Oumuamua before they arrive, providing us with more time to study them from afar — or even prepare a fly-by mission.


T. M. Eubanks 2019 ApJL 874 L11. doi:10.3847/2041-8213/ab0f29