New research has uncovered the origins of ‘Oumuamua — the first interstellar object spotted roaming within our solar system — implying there may be many more objects in the cosmos like the so-called ‘space cigar.’

The interstellar visitor ‘Oumuamua caused quite a stir when it was first when spotted by astronomers on the 19th of October 2017. Not only did this excitement arise from the fact that it was a visitor from outside the solar system, but some also from the fact that the object — officially designated 1I/2017 U1 — possessed completely unexpected qualities for such body. The most striking of these features — an extremely unusual shape, not expected for an asteroid or comet, that resulted in it being nicknamed the ‘space cigar.’

Its elongated shape and other peculiarities led to speculation that ‘Oumuamua could be some form of an alien object, with even wild suggestions of a probe or ship lurking beneath its rocky exterior thrown around. Whilst the absence of any unexpected radio waves from the object quickly to these speculations to rest, there was clearly still a mystery to be solved regarding where ‘Oumuamua had come from and how it had formed.

New research suggests a formation mechanism for ‘Oumuamua, which though more naturalistic than suggestions of construction by alien engineers, is no less exciting.

An artist’s impression of ‘Oumuamua overlaid with a simulation of the tidal disruption scenario proposed by Zhang and Lin. Image credit: NAOC/Y. Zhang; (background: ESO/M. Kornmesser))

A paper published in the latest edition of the journal Nature Astronomy authored by Yun Zhang, National Astronomical Observatories of the Chinese Academy of Sciences, and Douglas Lin, University of California, Santa Cruz, suggests that ‘Oumuamua was created from the fragments of a planetesimal — a small planetary body — which strayed too close to its parent star and was ripped apart by the resultant tidal forces.

“It is really a mysterious object, but some signs, like its colours and the absence of radio emission, point to ‘Oumuamua being a natural object,” says the paper’s main author Zhang.

The model put forward by the paper also addresses ‘Oumuamua’s outlandish characteristics including its odd, cigar-like shape and its other unusual qualities.

“Our objective is to come up with a comprehensive scenario, based on well understood physical principles, to piece together all the tantalizing clues,” adds Lin, professor emeritus of astronomy and astrophysics at UC Santa Cruz. “We showed that ‘Oumuamua-like interstellar objects can be produced through extensive tidal fragmentation during close encounters of their parent bodies with their host stars, and then ejected into interstellar space”

Matthew Knight, astronomer and co-leader of the ‘Oumuamua International Space Science Institute team: “[This study] does a remarkable job of explaining a variety of unusual properties of ‘Oumuamua with a single, coherent model.”

It isn’t just its shape that make ‘Oumuamua extraordinary, the interstellar visitor displayed so many odd and unexpected characteristics that researchers have commented that it is like nothing else found in the solar system. For example, it was experiencing an acceleration that wasn’t a result of gravity, tumbling over itself over a period of every few hours, and low velocity for an object that had been ejected from a distant star system.

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

Beyond its odd motion, researchers had expected ‘Oumumua to take the appearance of an icy-comet, but observations indicated that lacked many comet-like features and more closely resembled an asteroid with a dry rocky surface.

The most notable by its absence was the nebulous cloud that usually surrounds a comet when it passes a hot body such as a star. This envelope — formally known as a coma — is caused by the sublimation of materials beneath the surface of the comet and accounts for comets’ distinctive tails. The lack of such a coma indicates that ‘Oumuamua is not sublimating much material even when heated by its close approach to the Sun. The lack of a distinctive tail also explains why the object managed to make it through the solar system without being detected, as comas usually make comets quite visible.

The lack of coma has a deeper significance, however, as it challenges the mechanism by which ‘Oumuamua was thrown out of its home star system. 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.

As ‘Oumuamua has a dry appearance, similar to rocky bodies like the solar system’s asteroids, a different ejection scenario must be responsible for setting it on its interstellar jaunt.