Yale University astronomers Gregory Laughlin and Malena Rice propose that interstellar objects such as the interstellar asteroid ‘Oumuamua and the interstellar comet 2I/Borisov could be icy planetesimals ejected by long-period giant protoplanets.
An artist’s impression of ‘Oumuamua. Image credit: M. Kornmesser / ESO.
When a star is newly formed, it is surrounded by a thin, rotating protoplanetary disk of dense gas and dust.
The disk is a volatile environment in which gas and dust are heated up by the young star, as well as the star’s gravitational energy, leading to movement, collisions, and eventually, the formation of planets.
Although most known planets form close to their star, there are some that develop much farther away and create large gaps in the protoplanetary disk.
“Those more distant planets are able to fling out material that could leave their home solar systems,” the astronomers said.
“However, they are also much more difficult to directly observe than their closer-in counterparts, which is why not many of these planets have been confirmed.”
To test their theory, Professor Laughlin and Rice looked at three protoplanetary disks from the Disk Substructures at High Angular Resolution Project (DSHARP), which focuses on images of 20 nearby protoplanetary disks taken by the Atacama Large Millimeter/submillimeter Array (ALMA).
“We were looking for disks in which it was pretty clear a planet was there,” Rice said.
“If a disk has clear gaps in it, like several of the DSHARP disks do, it’s possible to extrapolate what type of planet would be there. Then, we can simulate the systems to see how much material should be ejected over time.”
“This idea nicely explains the high density of these objects drifting in interstellar space, and it shows that we should be finding up to hundreds of these objects with upcoming surveys coming online next year,” Professor Laughlin said.
Beyond the mere novelty of noticing interstellar objects passing through our Solar System, the idea of observing such objects offers major possibilities for advancing our knowledge of the cosmos.
Unlike many astronomical discoveries, in which data is observed and interpreted from tremendous distances, interstellar objects are an up-close look at another part of the galaxy.
“You’re not looking at a distant star through a telescope,” Rice said.
“This is actual material that makes up planets in other solar systems, being flung at us. It’s a completely unprecedented way to study extrasolar systems up close — and this field is going to start exploding with data, very soon.”
The study will be published in the Astrophysical Journal Letters.
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Malena Rice & Gregory Laughlin. 2019. Hidden Planets: Implications from ‘Oumuamua and DSHARP. ApJL, in press; arXiv: 1909.06387
