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That interstellar comet spotted last year is weirder than expected

Published Apr 21st, 2020 10:28PM EDT
interstellar comet
Image: Gemini Observatory/NSF/AURA

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  • Interstellar comet 2I/Borisov is packed with carbon monoxide, making it a real weirdo when compared to comets from our solar system.
  • Scientists using high-powered telescopes observed the comet’s emissions and found carbon monoxide as well as hydrogen cyanide.
  • Future observations of new interstellar comets will be the only way to determine how unique 2I/Borisov truly is.
  • Visit BGR’s homepage for more stories.

When an amateur astronomer spotted what appeared to be only the second interstellar object ever observed by mankind, it was an incredibly big deal. The object, later confirmed to be a comet and named 2I/Borisov, definitely originated from outside of our solar system, and researchers have been studying it for months.

Now, after observation campaigns from both the Hubble Space Telescope and Chile’s Atacama Large Millimeter/submillimeter Array (ALMA), scientists have enough data to begin to describe what the comet is made of, and perhaps even offer us some hints as to its origins.

The first interstellar visitor to be spotted by humans was the bizarre Oumuamua, a cigar-shaped mass of… something that came cruising through our system and around the Sun so fast we didn’t even spot it until it was already on its way back out. Researchers had precious little time to study it as it sped away, but everything they learned about it seemed to generate more questions than answers.

By comparison, 2I/Borisov appeared pretty normal, at least at first. It wasn’t oddly shaped and, as far as astronomers could tell, it was a lot like the kinds of comets we see here in our own system. However, subsequent observations revealed the comet to be truly alien, and in a new paper published in Nature Astronomy, a team of scientists explains just how strange it is.

The team observed emissions from the comet which allowed them to estimate the abundance of various compounds present within it. What they found was that 2I/Borisov is made up of hydrogen cyanide, which the team was expecting, but it’s also absolutely packed with carbon monoxide. This, the scientists say, suggests the comet formed in a region of space that is incredibly cold, below -420 degrees Fahrenheit.

“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,” Martin Cordiner, lead author of the paper, said in a statement. “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.”

Now, the scientists have to grapple with another question: Is 2I/Borisov a good representative of most interstellar comets, or a total oddball? Are the comets we see in our own system unique, or is this sole interstellar visitor a rarity? We’ll have to wait for additional comets to arrive from elsewhere before we know.

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