WASHINGTON, March 23 (Reuters) – The first interstellar object to visit our solar system, the strange comet ‘Omuamua’ has been the object of fascination since its discovery in 2017, including its curious acceleration as it moves away from the Sun.
Hypotheses floated in light of its unexpected behavior, including quick speculation that it might actually be an alien spacecraft. A new study offers a more sobering explanation – ‘Omuamua’s speed increased as hydrogen gas was released as the comet heated up in sunlight.
‘Oumuamua (pronounced oh-MOO-uh-MOO-uh) lacks the tail of gas and dust characteristic of many comets. It was previously described as cigar-shaped, but is now thought to resemble a rock pancake. Smaller than originally estimated, it is now approximately 375 feet (115 meters) by 365 feet (111 meters), about 60 feet (19 meters) thick.
“Oumuamua was born like other comets — a small object formed during the early stages of planet formation — as a large, icy space rock,” the researchers said.
After it was somehow ejected from its solar system, the comet’s chemistry changed because it was hit by high-energy radiation as it passed through interstellar space. This turned some of the comet’s ice — frozen water — into hydrogen gas, which became trapped in its remaining ice.
‘Oumuamua then warmed up as it passed through our inner Solar System, reorganizing the comet’s icy composition and releasing trapped hydrogen gas – which kicked up a bit as ‘Oumuamua moved away from the Sun. The release of this hydrogen in a process called outgassing does not result in a visible tail.
“The key discovery is that ‘Omuamua may have started as a water-icy planet, similar to solar system comets. This model can explain ‘Omuamua’s strange behavior without resorting to any exotic physics or chemistry,” the university said. Berkeley, California astrophysicist Jenny Berkner is lead author of the research published in the journal this week Nature.
“What we expect for an interstellar comet is the simplest explanation and fits all the data precisely,” said study co-author Darryl Seligman, a postdoctoral fellow in planetary science at Cornell University.
‘Oumuamua, whose name means a messenger from afar in the native Hawaiian language, was first detected by the University of Hawaii’s Pan-STARRS1 telescope.
“We don’t know where it came from, but it probably traveled less than 100 million years ago. It had a red color, similar to the colors of many smaller bodies in the Solar System. It has now passed Neptune. It’s on its way out of the Solar System,” Bergner said.
A second interstellar object, Comet 2I/Borisov, was discovered visiting our Solar System in 2019. It looks like a regular comet.
These alien interlopers may be more common than previously known. Once a new astronomical observatory under construction in Chile starts operating as planned next year, between one and two interstellar objects could be discovered in our solar system each year, researchers said.
Reporting by Will Dunham, Editing by Rosalba O’Brien
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