‘Oumuamua’ – the first interstellar visitor to be observed in the solar system – has a dry, organic layer protecting its icy interior from vapourising, and is very similar to the minor planets in our system, scientists say.

Worldwide investigations into the mysterious, cigar-shaped object that passed close to Earth show that the way our planets and asteroids are formed is very similar to the
systems around other stars in our galaxy. Since the object was spotted in October, astronomers have been trying to piece together a profile of the strange visitor, which has been named ‘Oumuamua’.

Researchers from Queen’s University Belfast in the UK measured the way that ‘Oumuamua’, reflects sunlight, and found it similar to icy objects covered with a dry crust. This is because ‘Oumuamua’ has been exposed to cosmic rays for millions, or even billions, of years, creating an insulating organic-rich layer on its surface.

The research, published in the journal Nature Astronomy, suggests that Oumuamua’s dry crust could have protected its icy interior from being vaporised – even though the object was just over 37 million kilometres from the Sun in September when it zipped past.

“We have discovered that the surface of ‘Oumuamua’ is similar to small solar system bodies that are covered in carbon-rich ices, whose structure is modified by exposure to
cosmic rays,” said Alan Fitzsimmons, Professor at Queen’s University Belfast in the UK.

“We have also found that a half-metre thick coating of organic-rich material could have protected a water-ice-rich comet-like interior from vapourising when the object was heated by the sun, even though it was heated to over 300 degrees centigrade,” said Fitzsimmons.

Researchers observed ‘Oumuamua’ while it was still within reach of the largest telescopes in the world. They found the object was the same colour as some of the icy minor planets they had been studying in the outskirts of our solar system. This implies that different planetary systems in our galaxy contain minor planets like our own.

Working together, the researchers have been able to uncover some very important facts about ‘Oumuamua’. “We’ve discovered that this is a planetesimal with a well-baked crust that looks a lot like the tiniest worlds in the outer regions of our solar system, has a greyish red surface and is highly elongated, probably about the size and shape of the Gherkin skyscraper in London,” said Michele Bannister from Queen’s University.

“It’s fascinating that the first interstellar object discovered looks so much like a tiny world from our own home system,” Bannister said. “This suggests that the way our planets and asteroids formed has a lot of kinship to the systems around other stars,” she said.


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