New study: Strange interstellar object ‘Oumuamua could be hydrogen-burping comet

Researchers have speculated about what ‘Oumuamua is since the reddish, cigar-shaped galactic guest was first observed nearly six years ago by the Pan-STARRS1 telescope atop Haleakalā on Maui.

The strange object, later called ‘Oumuamua (which roughly translates to “scout” in Hawaiian), was the first known interstellar object to visit the solar system. An article in Space.com said from the moment of its discovery it was a “weird object — weird orbit, weird speed, weird properties.”

Some have even suggested the “scout from the distant past” could be an alien mothership harboring tiny drones that could have visited Earth as it passed by on its space odyssey.

According to a new study, the answer to the cosmic conundrum involving the interstellar enigma discovered in October 2017 by astronomers at the University of Hawai‘i’s Institute for Astronomy could have more to do with elemental expulsion — almost like hydrogen burps — than extraterrestrials.

The study published on March 22 in the journal Nature suggests that ‘Oumuamua, a more than 300-foot oblong object that likely traveled through the Milky Way for hundreds of millions of years before becoming the first visitor to our solar system from another star system, is just a comet.

The study was by University of California at Berkeley astrochemist Jennifer Bergner and Cornell University’s Darryl Seligman.

The mystery that has surrounded the object, which is so far away from us now that it can no longer be observed, mostly stems from its strange movements.

‘Oumuamua lacked the familiar tail of dust or gas normally associated with comets because of the outgassing of some kind of material such as nitrogen or carbon dioxide. At the same time, it appeared to be slightly accelerating as it made its way past the sun.

“Although typical cometary activity tracers were not detected, ‘Oumuamua showed a notable non-gravitational acceleration,” the new study says. “So far, there has been no explanation that can reconcile these constraints.”

Because non-outgassing explanations require fine-tuning and/or unrealistic power production from another source, Bergner and Seligman claim the object’s acceleration can be explained by the release of trapped hydrogen within ‘Oumuamua.

“‘Oumuamua began as an icy planetesimal that was irradiated at low temperatures by cosmic rays during its interstellar journey and experienced warming during its passage through the solar system,” their research says.

As the water ice inside, which has a structure that contains pockets where gas can collect, warms from the solar radiation, its structure changes and those pockets where hydrogen can hide are lost. As pockets collapse and cracks form, the trapped hydrogen would leak into space, pushing the object along. Gas pressure releasing — the hydrogen burps — at different locations and times can change a comet’s trajectory aside from gravitational forces.

“This explanation is supported by a large body of experimental work showing that [molecular hydrogen gas] is efficiently and generically produced from [water] ice processing, and that the entrapped [molecular hydrogen gas] is released over a broad range of temperatures,” the new study says. “We show that this mechanism can explain many of ‘Oumuamua’s peculiar properties … . This provides further support that ‘Oumuamua originated as a planetesimal relic broadly similar to solar system comets.”

Bergner and Seligman’s research supports a 2018 study by a team led by Marco Micheli of the European Space Agency’s SSA-NEO Coordination Centre and Karen Meech with the UH Institute for Astronomy, which also claimed that ‘Oumuamua, first thought to be an asteroid, behaves the same way as any ordinary comet.

While the new study is an “interesting and creative idea,” Meech told NPR in a March 22 story that she still thinks the object simply released enough water, carbon dioxide and carbon monoxide to explain its movement, it just wasn’t detected.

“What a lot of people don’t realize is that in order to get a good spectrum to detect the gas, you usually have to have a pretty bright comet,” Meech said. “And ‘Oumuamua was not bright.”

It’s also possible the trail of fine dust usually associated with comets that instruments look for simply wasn’t being shed by the interstellar object.

Avi Loeb, the vocal Harvard astronomer who brought forth theories that ‘Oumuamua could be an alien spacecraft, isn’t sold on the new study and its comet explanation, but said in a recent essay he wrote for Medium that it’s fantastic to see continuing interest from mainstream astronomy to explain the anomalous acceleration of the object more than 5 years after its discovery.

“It is good to have alternative models at hand as we search for the next `Oumuamua,” Loeb wrote.

The next interstellar visitor to our solar system might provide more answers, especially now that there is a wealth of testable ideas, Meech said. Some researchers have even already designed ways to intercept one.

“When ʻOumuamua was discovered, the astronomy community gathered as much data as possible, but ultimately, the object was just not visible long enough to answer all our questions,” said astronomer Ken Chambers, director of the Pan-STARRS observatories, in 2018. “With Pan-STARRS monitoring the skies, we hope to discover more ʻOumuamua-like objects in the future and begin to answer the really interesting questions about this class of objects.”