Since 2017, when astronomers in Hawaii discovered an object they called Oumuamua (“explorer” in Hawaiian) traveling through the solar system, what it was has been the subject of discussion.
The telescopes only saw a dot tumbling. Astronomers deduced that it was reddish, shaped like a cigar or hotcake, and perhaps a few hundred meters long.
Oumuamua was classified as an asteroid, as it did not exhibit the crackling and flashing typical of comets. (Comets are basically dirty snowballs; when heated by sunlight, they emit jets of steam, carbon dioxide and dust, which create bright tails or comas.) There was no evidence of gas or dust around the object, and radio telescopes heard nothing of it.
However, further analysis revealed that something was causing Oumuamua to accelerate as it left the solar system, leaving scientists baffled.
Now, two astronomers have found what they call “a surprisingly simple explanation” for Oumuamua's behavior: the object was a comet after all, powered by minuscule amounts of hydrogen gas gushing from an icy core.
This may explain Oumuamua's peculiar properties, write Jennifer Bergner, an astrochemist at the University of California, Berkeley, and Darryl Z. Seligman, of Cornell University in upstate New York, in an article in Nature. “This provides further support that Oumuamua originated as a planetesimal relic very similar to comets in the solar system.”
In an email, Karen Meech, a comet expert at the University of Hawaii Institute for Astronomy, called the paper “a very interesting explanation.
“I'm not willing to say it 'resolves' the issue — the smoking gun there would be having detected hydrogen spectroscopically,” she added.
The controversy is unlikely to evaporate anytime soon. Avi Loeb, an astronomer at Harvard University who has proposed that Oumuamua could have been some extraterrestrial artifact, was quick to disagree with the article.
“The authors of the new study claim that this was a water ice comet even though we did not see the comet's tail,” Loeb said via email. “This is like saying that an elephant is a zebra without stripes.”
Bergner, an expert in the chemistry of ice in outer space, wondered whether gaseous molecular hydrogen, the most abundant and volatile element in the universe, could have propelled the comet. But where would the gas have come from?
“Because Oumuamua was so small, we think it actually produced enough force to drive this acceleration,” Bergner said.
And any dust in the ice would be trapped there, eliminating much of the spectacle of the comet's tail.
By: DENNIS OVERBYE
BBC-NEWS-SRC: http://www.nytsyn.com/subscribed/stories/6644981, IMPORTING DATE: 2023-04-05 00:20:08
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