Borisov, a comet from another star system, was surrounded by a cloud of poisonous ice that had to have formed in a region of space colder than anything known to man.
Researchers from NASAs Goddard Space Flight Center found that it must have formed in the outer edges of its original star system – known as Kruger 60.
This would have been in an area of space where temperatures fall to a staggering -420 degrees Fahrenheit – cold enough for carbon monoxide (CO) to freeze.
NASA scientists say its 100,000 mile coma – a fuzzy outer layer of light surrounding the object – contains water and an unusually large amount of carbon monoxide.
A team from Yale University captured this ‘close-up’ image of the comet on the November 24, using the Keck Observatory’s low-resolution imaging spectrometer
The cold temperatures of interstellar space would have preserved its chemicals for millions or even billions of years while it journeyed across the universe.
When it got within around 190 million miles of our Sun the warmth eventually caused the ice to vaporise and the coma to shrink in size.
It had up to 26 times as much CO than that of the average solar system comet.
According to NASA researchers this means it was born where the volatile compound could be frozen into its nucleus.
Dr Martin Cordiner, of NASA’s Goddard Space Flight Centre in Maryland, said: ‘This is the first time we’ve ever looked inside a comet from outside our solar system.
‘It’s is dramatically different from most other comets we’ve seen before.’
On October 10, experts announced that they had found that Borisov had come from a twin star system dubbed ‘Kruger 60’, pictured in an artist’s impression, that lies 13 light years away
Comets spend most of their time at large distances from any star. Unlike planets their interior compositions change little over time due to the freezing temperatures.
The findings, published in the journal Nature Astronomy, could shed fresh light on the evolution of star systems including our solar system.
They are based on images of the trail of gas left by Borosov that were captured by the ALMA (Atacama Large Millimeter/submillimeter Array) telescope in Chile.
It detected normal quantities of HCN (hydrogen cyanide) – another molecule present in comets – but the CO readings came as a surprise to astronomers.
Co-author Dr Stefanie Millam, said it must have formed from material ‘very rich in CO ice’ which is only present at the lowest temperatures found in space.
The comet is more than half a mile wide and its tail nearly 100,000 miles long – meaning it would stretch round Earth 14 times.
Previous research has indicated it came from a twin star system dubbed ‘Kruger 60’ that lies 13 light years away from Earth.
It was probably ejected into interstellar space as a consequence of a near-collision with a planet in its original star system.
Co-author Dr Anthony Remijan, of the National Radio Astronomy Observatory in Charlottesville, Virginia, said ALMA is changing our understanding of the nature of comets and what they’re made of.
‘It’s only because of ALMA’s unprecedented sensitivity at submillimeter wavelengths that we are able to characterise the gas coming out of such unique objects,’ he said.
Carbon monoxide is one of the most common molecules in space – and is found inside most comets but every comet varies in how much CO is found inside them.
The comet’s tail, shown in the new image, is nearly 100,000 miles long, which is 14 times the size of Earth. The tail is made up of an unusually high level of carbon monoxide
It can be related to where in the solar system a comet was formed – or how often the orbit brings it closer to the Sun leading to the evaporation of more ice.
‘If the gases we observed reflect the composition of Borisov’s birthplace, then it shows 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 Dr Cordiner.
This region can be compared to the Kuiper Belt – a cold region of icy bodies beyond Neptune in the Solar System.
The team can only speculate about the kind of star that hosted Borisov’s planetary system as they haven’t observed it directly.
This composite image of Borisov was captured in September 2019. Astronomers don’t know whether it’s nitrogen dioxide heavy coma is usual for interstellar objects or whether Borisov is unique among the stars
Dr Cordiner said: ‘Most of the proto-planetary disks observed with ALMA are around younger versions of low-mass stars like the Sun.
‘Many of these disks extend well beyond the region where our own comets are believed to have formed – and contain large amounts of extremely cold gas and dust. It’s possible that Borisov came from one of these larger disks.’
It reached 21 miles a second as it travelled through our solar system – suggesting it was ‘kicked out’ from its host system by a passing star or giant planet.
It then spent millions or billions of years on a cold, lonely voyage through interstellar space before it was discovered by chance on August 30, 2019 by Crimean telescope maker Gennady Borisov.
Borisov was discovered in 2019 and was only the second interstellar traveller to be spotted in the solar system – following the discovery of Oumuamua in 2017.
Borisov is the second-known visitor from outside our solar system — joining the cigar-shaped asteroid Oumuamua, which was detected on October 19, 2017
Oumuamua was already on its way out when it was spotted in 2017 – making it difficult to reveal details about whether it was a comet, asteroid or something else.
The presence of an active gas and dust coma surrounding Borisov made it the first confirmed interstellar comet.
Until others are observed its unusual composition cannot easily be explained – and raises more questions than answers, according to the NASA team.
‘Borisov gave us the first glimpse into the chemistry that shaped another planetary system,’ said Dr Milam.
‘But only when we can compare the object to other interstellar comets, will we learn whether Borisov is a special case, or if every interstellar object has unusually high levels of CO.’
A paper published by another team in the same journal based on observations from the Hubble Space Telescope (HST) confirmed the comet has between 0.7 and 1.7 times as much CO as water – making it unique.
WHAT IS 2I/BORISOV?
2I/Borisov is a comet that came from outside the solar system.
It is believed to have a core that is around 0.9–4.1 miles (1.4–6.6 kilometres) in diameter.
The interstellar comet 2I/Borisov, pictured, which is currently visiting our solar system is harbouring water that came from another star system, a study has found
The comet was spotted by amateur astronomer Gennady Borisov from Crimea’s MARGOT observatory on August 30, 2019.
It will make its closest pass to the Sun on December 8, 2019 — but will not get close to any of the planets in the solar system.
2I/Borisov will leave the solar system in the direction of the constellation of Telescopium.
According to Polish researchers, it likely originated from the binary red dwarf star system Kruger 60.
The comet is only the second interstellar visit to have been spotted.
The first was the cigar-shaped asteroid 1I/’Oumuamua, which was detected on October 19, 2017.