he first ever interstellar visitor to our solar system is wrapped in a layer of organic insulation, scientists have said.
Oumuamua has enthralled astronomers and the public since it flew through the solar system in October.
As the first alien rock to travel here from another star, it was immediately recognised as highly unusual – but as scientists learn more about the object, they are discovering how strange it actually is.
Its strangeness has even led to suggestions it could be an alien artefact, rather than just an incredibly abnormal natural object.
Very little is known about what Oumuamua is, where it came from, and what it is made up of. Scientists had relatively little time to study the object as it passed through our solar system, and they are continuing to analyse the data that was obtained.
Before the rock arrived, scientists had expected that visitors of its kind would look like comets as they flew through the solar system. Such items would be made up of ice that would leave a visible stream behind them as they travelled past hot stars, they suggested.
But when Oumuamua flew past, no such activity was detected, despite flying close to the sun on its journey.
Now scientists taking part in different studies have released detailed findings on what the rock looks like and what it might be made of.
While it is probably an icy body as expected, it appears to be wrapped in an organic coat that shields the frozen water inside from being hit by the sun, according to the new research.
“In the end this was a nice result because we’ve expected all along that the majority of objects that would visit our solar system would be icy in nature,” said Alan Fitzsimmons from Queen’s University Belfast and the lead author of one of two major new studies into Oumuamua.
“It has been a puzzle that this thing looked like a big lump of rock.
“Our study says that this object could well be icy in nature but we didn’t detect that ice due to the fact it’s been baked by energetic radiation between the stars for hundreds of millions of years, or even billions of years.”
It is not certain that Oumuamua has any ice at all – the conclusion of Professor Fitzsimmons’ work is only that it can’t be ruled out. But that is because it is wrapped by its strange organic coat, and scientists can only see the very thinnest layer at the top of the object.
The coat was examined by using spectroscopy, which looks at the light being reflected from its surface and splits it down into its wavelengths. By looking at those measurements, scientists can work out what the object might be composed of.
“What we didn’t see is the signatures of the rocks you’d usually find on Earth, or you might find on the inner asteroid belt surrounding our sun,” Professor Fitzsimmons said.
It appeared red, but when looked at through infrared light it became more grey in colour. That was expected – it is what would normally come back from icy objects in our own solar system – but there did not actually appear to be any ice water coming off the surface.
Normally, ice is expected fall off such an object as it flies by the sun and the ice is warmed, forming a miniature comet. [….]