Analysis of observations of the interstellar comet 2I / Borisov, carried out with the ALMA radio telescope array on December 15 and 16, 2019, showed an unusual chemical composition of the comet, different from that of comets in the solar system. The new study was published on April 20, 2020 in the journal Nature Astronomy.
The study was conducted by a team of scientists led by Martin Cordiner and Stephanie Milam of NASA's Goddard Space Flight Center in Greenbelt. It showed that the gas exiting the comet contained an unusually high amount of carbon monoxide (CO).
The CO concentration was higher than any comet ever discovered within 2 AU. from the Sun (within less than 300 million kilometers). The CO concentration in comet Borisov was estimated as 9–26 times higher than that of the average comet of the Solar System.
“This is the first time we have studied the composition of a comet outside the solar system,” astrochemist Martin Cordiner said. “It is drastically different from most other comets we've seen before.”
ALMA has detected two molecules in the comet's gas: hydrogen cyanide (HCN) and carbon monoxide (CO). Scientists expected to see HCN present in comet 2I / Borisov in quantities similar to those found in comets in the solar system. However, their surprise knew no bounds when they discovered such a high CO content.
“The comet was most likely formed from solid CO-enriched material that is only present at the lowest temperatures found in space: below -420 degrees Fahrenheit (-250 degrees Celsius),” planetary scientist Stephanie Milam said.
Carbon monoxide is one of the most abundant molecules in space and is found in most comets. Nevertheless, there is a huge difference in the concentration of CO in comets, and so far no one can answer the question – why. Scientists believe that this may be partly due to the place of formation of the comet and the frequency of its approach to the orbit of a particular star.
