Interstellar comet 2I/Borisov appears to have a large amount of water

Interstellar comet 2I/Borisov seen by Hubble (Image NASA, ESA, D. Jewitt (UCLA))
Interstellar comet 2I/Borisov seen by Hubble (Image NASA, ESA, D. Jewitt (UCLA))

An article published in the “Astrophysical Journal Letters” reports the detection of what have been interpreted as traces of water emitted by interstellar comet 2I/Borisov. A team of researchers led by Adam McKay of NASA’s Goddard Space Flight Center used the Apache Point Observatory in New Mexico to study the light reflected from the comet detecting the “signature” of oxygen in large amounts. The most likely explanation for the presence of this element is that the ultraviolet light from the Sun broke the water molecules emitted into oxygen and hydrogen.

Comet 2I/Borisov, initially designated as C/2019 Q4, was discovered on August 30, 2019 by the amateur astronomer Gennady Borisov and after some observations the data about its orbit started suggesting its interstellar origin. confirmed by follow-up observations.

The first studies of comet 2I/Borisov allowed to detect some molecules such as those of carbon and cyanide. A more general study indicated that it’s similar to the solar system’s comets, but how much? We’re used to considering the presence of water in abundance as part of comets’ nature but we can’t take it for granted in the study of an interstellar comet therefore Adam McKay, with the collaboration of Anita Cochran, Neil Dello Russo and Michael DiSanti, tried to look for evidence of the presence of water on this object.

Several photos of interstellar comet 2I/Borisov, including the one that so far is the sharpest taken by the Hubble Space Telescope on October 12 at a distance of about 420 million kilometers from Earth, showed that it’s active, with a coma surrounding the nucleus and a tail.

Adam McKay and his collaborators observed comet 2I/Borisov with the 3.5 meter ARC telescope at the Apache Point Observatory of the Astrophysical Research Consortium (ARC) using in particular the ARCES (ARC Echelle Spectrometer) instrument to analyze the spectrum of the light from 2I/Borisov. The result of the analysis is that the spectrum shows oxygen emissions in large amounts.

According to the researchers, that oxygen derives from water vapor molecules emitted by comet 2I/Borisov during its activity that are broken by ultraviolet light from the Sun. In theory it could derive from carbon monoxide or carbon dioxide molecules broken in the same way but the activity of 2I/Borisov seems more consistent with what we can expect from the emission of water, which sublimates under the Sun’s action.

The calculations regarding water production by interstellar comet 2I/Borisov are currently approximate, applying models created for the solar system’s comets. Their correctness in the study of 2I/Borisov must be verified with follow-up observations and spectroscopic analyzes. It’s still approaching the Sun so there will still be many possibilities to improve our knowledge of this object arrived from another star system.

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