Scientists explain the strange acceleration of the space comet ‘Oumuamua’

WASHINGTON (Reuters) – Twisted comet Oumuamua, the first interstellar object found visiting our solar system, has been a subject of interest since it was spotted in 2017, including its intriguing acceleration as it hurtles away from the sun.

Hypotheses have been put forward in light of its unpredictable behavior, including fleeting speculation that it may in fact be an alien spacecraft. A new study offers a more realistic explanation – that ‘Oumuamua’s acceleration was due to the release of hydrogen gas as the comet warmed in sunlight.

Oumuamua (pronounced oh-moo-ah-moo-ah) lacks the tail of gas and dust that characterizes many comets. It was previously described as cigar-shaped but is now thought to resemble a rock pie. Smaller than originally estimated, it is now pegged at about 375 feet (115 m) by 365 feet (111 m), and about 60 feet (19 m) thick.

The researchers said it appears that “Oumuamua was born like many other comets as a so-called planetary – a small object that formed in the early stages of planet formation – and was essentially a large icy space rock.

After it was somehow ejected from its original solar system, they said, the comet’s chemistry changed as it was bombarded with high-energy radiation as it ventured through interstellar space. This converted some of the comet’s ice – frozen water – into hydrogen gas trapped within the remainder of its ice.

Oumuamua then heated up as it passed through our inner solar system, causing the comet’s icy structure to rearrange and to release trapped hydrogen gas – giving Oumuamua a little kick as it headed away from the sun. The release of this hydrogen in a process called outgassing will not cause a visible tail.

“The main finding is that ‘Oumuamua may have started as an icy, water-rich planet much like solar system comets. This model could explain ‘Oumuamua’s strange behavior without having to resort to any exotic physics or chemistry.” California, Berkeley astrophysicist Jenny Bergner, lead author of the research published this week in the journal nature.

“The simplest explanation, which is exactly what we would expect for an interstellar comet, fits all the data without fine-tuning,” said study co-author Daryl Seligman, a postdoctoral fellow in planetary sciences at Cornell University.

Oumuamua, whose name in the indigenous Hawaiian language denotes a messenger coming from a great distance, was first detected by the University of Hawaii’s Pan-STARRS1 telescope.

“We don’t know where it originated but it may have been traveling through interstellar space less than 100 million years ago. Its reddish color corresponds to the colors of many small bodies in the solar system. It currently bypasses Neptune on its way out of the solar system.”

A second interstellar object, Comet 2I/Borisov, was discovered during a visit to our solar system in 2019. This object looked like a typical comet.

These alien intruders may be more common than previously known. One to two interstellar objects could be detected each year in our solar system, the researchers said, once a new astronomical observatory now being built in Chile begins operations as planned next year.

(Reporting by Will Dunham; Editing by Rosalba O’Brien)

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