Sorry, it wasn't an alien spacecraft, after all. Study finds explanation for an unusual behavior of a visitor called Oumuamua.

Was it alien space junk? A wandering interstellar asteroid? Or a weird comet from another sun?

Ever since 2017, when astronomers in Hawaii discovered an object they called Oumuamua [ Hawaiian for ''scout'' ] zipping pass through the solar system, they have been arguing about what it was.

Telescopes saw only a tumbling dot that was already on its way back into the interstellar dark. Astronomers deduced that it was reddish, cigar-or-pancake-shaped and perhaps a few hundred meters long.

To date, all the comets observed in our solar system have ranged from around a half-mile to hundreds of miles across. [Halley's comet is about seven miles wide, about 11 kilometers.]

Initially Oumuamua was pegged as an asteroid, as it exhibited none of the sizzle and flash typical of comets. [Comets are basically dirty snowballs; when warmed 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 when pointed at it.

But further analysis showed that something was making Oumuamua speed up as it exited the solar system, leaving scientists with a delicious puzzle.

NOW, two astronomers have found what they call ''a surprisingly simple explanation'' for Oumuamua's  behavior : The object was a comet after all, propelled by minuscule amounts of hydrogen gas spurting from an icy core.

''We show that this mechanism can explain many of Oumuamua's peculiar properties without fine-tuning,'' Jennifer Bergner, an astrochemist at the University of California, Berkeley, and Darryl Z. Seligman, of Cornell University, wrote in a paper published in Nature.

'' This provides further support that Oumuamua originated as a planetestimal relic broadly similar to solar system comets.

In a statement issued by the University of California, Berkeley, Dr. Seligman said : ''What's beautiful about Jenny's idea is that it's exactly what should happen to interstellar comets.

We had all these stupid ideas, like hydrogen icebergs and other crazy things, and it's just the most generic explanation.''

In an email, Karen Meech, a comet expert at the University of Hawaii Institute for Astronomy who has studied Oumuamua extensively, called the paper ''a very interesting explanation.''

The World Students Society thanks author Dennis Overbye.


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