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New Theory Explains Mysterious Interstellar Object ‘Oumuamua

A new scenario based on computer simulations accounts for all of the observed characteristics of the first known interstellar object to visit our solar system. Since its discovery in 2017, an air of mystery has surrounded the first known interstellar object to visit our solar system, an elongated, cigar-shaped body named ‘Oumuamua (Hawaiian for “a messenger from afar arriving first”).

How was it formed, and where did it come from? A new study published in Nature Astronomy offers a first comprehensive answer to these questions.

This illustration shows the tidal disruption process that can give rise to ‘Oumuamua-like objects. (Image credit: NAOC/Y. Zhang)

First author Yun Zhang at the National Astronomical Observatories of the Chinese Academy of Sciences and co-author Douglas N. C. Lin at UC Santa Cruz, used computer simulations to show how objects like ‘Oumuamua can form under the influence of tidal forces like those felt by Earth’s oceans. Their formation theory explains all of ‘Oumuamua’s unusual characteristics. Lin, professor emeritus of astronomy and astrophysics at UC Santa Cruz, said:

Mysterious Object

Discovered on October 19, 2017, by the Panoramic Survey Telescope and Rapid Response System 1 (Pan-STARRS1) in Hawaii, ‘Oumuamua is absolutely nothing like anything else in our solar system, according to Zhang. Its dry surface, unusually elongated shape, and puzzling motion even drove some scientists to wonder if it was an alien probe. Zhang said:

Lin added:

Astronomers had expected that the first interstellar object they detected would be an icy body like a comet. Icy objects like those populating the Oort cloud, a reservoir of comets in the outermost reaches of our solar system, evolve at very large distances from their host stars, are rich in volatiles, and are often tossed out of their host systems by gravitational interactions. They are also highly visible due to the sublimation of volatile compounds, which creates a comet’s coma (or “tail”) when it is warmed by the sun.

An ‘Oumuamua-like object produced by a simulation of the tidal disruption scenario proposed by Zhang and Lin. (Image: NAOC / Y. Zhang; background: ESO / M. Kornmesser)

‘Oumuamua’s dry appearance, however, is similar to rocky bodies like the solar system’s asteroids, indicating a different ejection scenario. Other researchers have calculated that there must be an extremely large population of interstellar objects like ‘Oumuamua, Zhang said:

When a smaller body passes very close to a much bigger one, tidal forces of the larger body can tear the smaller one apart, as happened to comet Shoemaker-Levy 9 when it came close to Jupiter. The tidal disruption processes can eject some debris into interstellar space, which has been suggested as a possible origin for ‘Oumuamua. But whether such a process could explain ‘Oumuamua’s puzzling characteristics remained highly uncertain.

Computer Simulations

Zhang and Lin ran high-resolution computer simulations to model the structural dynamics of an object flying close by a star. They found that if the object comes close enough to the star, the star can tear it into extremely elongated fragments that are then ejected into the interstellar space. Zhang said:

The researchers’ thermal modeling showed that the surface of fragments resulting from the disruption of the initial body would melt at a very short distance from the star and recondense at greater distances, thereby forming a cohesive crust that would ensure the structural stability of the elongated shape. Zhang explained:

Observations of ‘Oumuamua showed no cometary activity, and only water ice is a possible outgassing source to account for its non-gravitational motion. If ‘Oumuamua was produced and ejected by the scenario of Zhang and Lin, plenty of residual water ice could be activated during its passage through the solar system. The resulting outgassing would cause accelerations that match ‘Oumuamua’s comet-like trajectory. Zhang said:

The researchers’ calculations demonstrate the efficiency of tidal forces in producing this kind of object. Possible progenitors, including long-period comets, debris disks, and even super-Earths, could be transformed into ‘Oumuamua-size pieces during stellar encounters.

An artist’s impression of ‘Oumuamua formation. (Image: YU Jingchuan from Beijing Planetarium)

This work supports estimates of a large population of ‘Oumuamua-like interstellar objects. Since these objects may pass through the domains of habitable zones, the possibility that they could transport matter capable of generating life (called panspermia) cannot be ruled out. Zhang said:

According to Lin:

U.S. Naval Academy astronomer Matthew Knight, who is co-leader of the ‘Oumuamua International Space Science Institute team and was not involved in the new study, said this work:

[Note: Materials may be edited for content and length.]

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  • Troy was born and raised in Australia and has always wanted to know why and how things work, which led him to his love for science. He is a professional photographer and enjoys taking pictures of Australia's beautiful landscapes. He is also a professional storm chaser where he currently lives in Hervey Bay, Australia.

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