Scientists report 'unusual' findings after scanning comet that visited from another solar system

'This is the first time we've ever looked inside a comet from outside our solar system, and it is dramatically different from most other comets we've seen before'

Scientists have peered at the chemicals inside an object from another solar system for the first time – and found "unusual" results.

Last year, a comet known as 2I/Borisov was spotted flying through our solar system, having come on an interstellar journey from another planetary system.

Now researchers have found that it was probably formed in a distant, cold part of its solar system, far from its home star.

Soon after it was discovered, researchers pointed the Atacama Large Millimeter/submillimeter Array (ALMA) towards it, in an attempt to scan it and understand what it may be made up of. That radio telescope – the largest in the world – is able to scan electromagnetic radiation and can help understand the chemical makeup of objects large and small elsewhere in the universe.

The observations showed that gas was coming out of the comet that contained unusually high amounts of carbon monoxide. There was more of the chemical than had been found in any comet near the sun, and may have been 26 times higher than the average solar system comet.

Usually, in comets found in our solar system, water is the most abundant molecule in the "coma" or gas cloud that surrounds them. But 2I/Borisov had as much as 1.7 times as much carbon monoxide as it did water, the scientists report.

"This is the first time we've ever looked inside a comet from outside our solar system," said astrochemist Martin Cordiner in a statement. "And it is dramatically different from most other comets we've seen before."

Such comets are fascinating to scientists in part because they spend much of their time a long way from any star, in very cold environments. As such, their interior makeup is relatively untouched, and could provide an insight into what happened when they were born in the early history of their solar systems.

In 2I/Borisov's case, scientists think it was kicked out from its home system, probably when it interacted with a passing star or planet. Since then, the cold environment intestellar space will probably have kept it preserved as it travelled on its way towards Earth, meaning that its makeup has probably remained as it was since its formation, possibly billions of years ago.

Alongside the carbon monoxide (CO) found in the comet, there was also hydrogen cyanide (HCN), scientists report in the new article published in Nature Astronomy. But researchers were less surprised by that discovery, since the HCN was found in roughly similar amounts to that in comets from our own solar system.

Carbon monoxide is also expected to be present in such objects, but not in such high amounts. The unusual findings could offer an insight into the conditions that gave birth to the interstellar comet.

"The comet must have formed from material very rich in CO ice, which is only present at the lowest temperatures found in space, below -420 degrees Fahrenheit (-250 degrees Celsius)," said planetary scientist Stefanie Milam.

As such, the object was likely formed in an extreme region, at a long distance from its star. Its home could be similar to the cold area beyond Neptune in our own solar system, the Kuiper Belt, which is host to numerous icy objects.

"If the gases we observed reflect the composition of 2I/Borisov's birthplace, then it shows that it may have formed in a different way than our own solar system comets, in an extremely cold, outer region of a distant planetary system," said Cordiner.

The object known as 2I/Borisov's arrived soon after the first known interstellar visitor, Oumuamua. But scientists had a much more limited chance to study that object, since it was only spotted as it was headed away from the solar system.

The findings are reported in two papers published in Nature Astronomy today: 'Unusually high CO abundance of the first active interstellar comet' and '2I/Borisov is a carbon monoxide-rich comet from another star'.