Discovered in 2017, ‘Oumuamua became the first observed interstellar object to zip through our solar system, and its appearance sparked questions scientists are still trying to answer.
‘Oumuamua was first spotted on 19 October 2017. A telescope in Hawaii spied it as it made its way past the Sun, reaching a top speed of 87 kilometers per second, or 54 miles per second —too fast to have originated in the Solar System. Astronomers named the object 1I/2017 U1 (‘Oumuamua), Hawaiian for “a messenger from afar arriving first.”
For several years, scientists speculated on what the strange interstellar object up to 400 meters long could actually be – was it an alien spacecraft? or possibly an asteroid?
No such object from beyond our Sun’s reaches had visited us before, with this interloper moving so fast it could not be bound to the Sun. ‘Oumuamua was also odd in that it looked like an asteroid but behaved like a comet.
Another odd thing about ‘Oumuamua was its strange acceleration as it hurtled away from the sun. All kinds of hypotheses were floated in light of its unexpected behavior, according to Reuters.
However, a new study published in the journal Nature last week has offered a more sober explanation – that ‘Oumuamua’s speed-up was due to the release of hydrogen gas as the comet warmed up in the sunlight.
The team of researchers says ‘Oumuamua was definitely a comet, albeit one with an unusual makeup. “We can explain a lot of the strange behavior,” says Jennifer Bergner, a chemist at the University of California, Berkeley, who led the study.
Bergner and her colleague Darryl Seligman, an astronomer at Cornell University, think they can now explain what happened. Their modeling shows ‘Oumuamua could have begun life as a regular water-rich comet around a nearby star, before being ejected.
They found that high-energy cosmic rays that pervade the Galaxy, emitted by supernovae and other energetic events, could have turned up to 30 percent of the comet’s water ice into hydrogen, which could have become trapped in ‘Oumuamua’s ice as it journeyed through interstellar space.
‘Oumuamua was accelerating as it moved, which would require more than just gravity. The object appeared to be pushed like comets are when they near the sun and the evaporation of their gas and dust by the sun’s heat causes a propulsive effect.
However, ‘Oumuamua didn’t look like a comet, nor did it have a tail or an envelope of gas and dust, called a coma, that all comets have, reports CNN News.
‘Oumuamua then was warmed up as it passed through our inner solar system, causing the comet’s ice structure to rearrange and releasing the trapped hydrogen gas.
This action gave ‘Oumuamua a little bit of a kick as it headed away from the sun. The release of this hydrogen in a process called outgassing would not cause a visible tail.
The simplest explanation, and exactly what we would expect for an interstellar comet, fits all of the data with no fine-tuning,” said Seligman, who is also a co-author in the study.
The study is “the most convincing model so far” for ‘Oumuamua, says Marco Micheli, an astronomer at the European Space Agency in Italy who was not involved with the work. The alien visitor, he says, was actually not so different from Solar System comets, Science.org. reports.
