Study offers answer for comet’s orbit that stumped astronomers

The strange outer- space object ’ Oumuamua flew through our solar system in 2017 and captured our imaginations.

Meaning “scout” or “messenger” in Hawaiian, ’ Oumuamua was the first known visitor from outside our solar system. It had no bright dust tail, like most comets, and had a peculiar shape – something between a cigar and a pancake.

But the object also had a weird orbit: It accelerated away from the sun in a way that astronomers could not explain, leading some to suggest it was an alien spaceship.

Now, in a study published Wednesday, the odd orbit of ’ Oumuamua can be explained by a simple physical mechanism that’s probably common among many icy comets: outgassing of hydrogen as the comet warmed in the sunlight.

’ Oumuamua was a comet traveling through interstellar space that was basically getting cooked by cosmic radiation, forming hydrogen as a result, said lead author Jennifer B. Bergner, an astrochemist at the University of California, Berkeley.

As it neared our sun, ‘ Oumuamua also warmed up and then released hydrogen, which slightly bent its path through our solar system.

The object was about a quarter- mile long, and astronomers first spotted it in October 2017 as it zipped through the inner solar system. Most comets are much bigger than ’ Oumuamua.

“Because ’ Oumuamua was so small, we think that it actually produced sufficient force to power this acceleration,” Bergner said.

Astronomers say the comet may well have been wandering through our Milky Way galaxy, unattached to any star system, for hundreds of millions of years before its chance encounter with our solar system.

“What’s beautiful about Jenny’s idea is that it’s exactly what should happen to interstellar comets,” said study coauthor Darryl Seligman, of Cornell University. “We had all these stupid ideas, like hydrogen icebergs and other crazy things, and it’s just the most generic explanation.”

Scientists believe interstellar comets such as ’ Oumuamua pass through our solar system about once a year, but they are faint and hard to spot.

The new study’s findings support theories that ’ Oumuamua may have originated as an icy planetesimal – a small object formed during the early stages of planet formation – similar to other solar system comets.

The study was published in the peerreviewed British journal Nature.

ESO/ M. KORNMESSER An artist’s impression of ’ Oumuamua. The unique object was discovered on Oct. 19, 2017, by the Pan- STARRS 1 telescope in Hawaii.