Oumuamua more likely an interstellar space shard than an alien spaceship - CNET

This artist's impression shows Oumuamua, an interstellar asteroid.

ESO/M. Kornmesser

The first object ever spotted visiting our solar system from beyond has perplexed scientists ever since it was discovered and dubbed Oumuamua back in 2017. Now a team of researchers thinks it has a plausible origin story that can explain the interstellar traveler's weird shape and motions.

You may recall that Oumuamua was an oblong object that tumbled end-over-end through space and sped up as it left our solar system. All this was very strange because the properties of gravity tend to shape most space objects to be more spherical and Oumuamua didn't have a coma like a comet that could help explain its acceleration as it fled our sun's influence. 

It was also bizarre that very respectable astronomers were making headlines by wondering aloud (and in print) if the odd visitor might be an artificial alien interloper. 

There's been no evidence to back up the alien hypothesis, but a pair of researchers ran some scenarios through computer simulations and came up with a formation theory that can explain all of Oumuamua's weirdness. 

"Our objective is to come up with a comprehensive scenario, based on well understood physical principles, to piece together all the tantalizing clues," University of California - Santa Cruz astronomer Douglas N. C. Lin explained in a release. 

Lin is co-author, along with Yun Zhang at the National Astronomical Observatories of the Chinese Academy of Sciences, of a new study published Monday in Nature Astronomy.

"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," Lin said.

Put more simply, when an object like a comet, a disk of debris or even a planet larger than Earth travels close enough to a star, the gravitational force of the star could tear it into elongated fragments that get tossed into interstellar space in the process. 

An illustration of how an object can be distorted or fragmented to form an 'Oumuamua-like shape. 

NAOC/Y. Zhang

Thermal modeling showed that the surface of the oblong space shards would be heated, melting any ice, only to recondense once in deeper in space, solidifying the object into its cigar-like shape. The simulations show that the object's violent encounter with a distant star could dry it out to the point that it contains too few volatile chemical compounds to produce a coma like a comet's, but could leave it with some buried water ice.

This is an important point because that hidden ice could have been heated as Oumuamua passed through our solar system enough to out-gas and explain the object's mysterious acceleration as it left our cosmic neighborhood. 

Perhaps the biggest implication of the study is that if it's right, Oumuamua isn't as weird as it first seemed. 

"The discovery of 'Oumuamua implies that the population of rocky interstellar objects is much larger than we previously thought," Zhang said. "On average, each planetary system should eject in total about a hundred trillion objects like Oumuamua." 

While the models indicate Oumuamua wasn't created by intelligent alien life, that doesn't mean objects like it can't transport the building blocks of life around the universe. It's thought that comets and other objects may pick up matter capable of generating life as they travel through habitable zones and seed it when they collide with planets -- a theory known as panspermia. 

"This is a very new field. These interstellar objects could provide critical clues about how planetary systems form and evolve," Zhang said.

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