Comet Borisov degassed 230 million liters of extrasolar water

The world of exoplanets fascinates us but, unfortunately, even if a fraction of Humanity is busy developing an interstellar probe project via the project Breakthrough Starshot, a photonic nanowire powered by beams laser for stars closest to Sun in the Alpha system of the Centaur, Homo sapiens is still taking its first steps out of its cradle, the Earth, in the Solar system.

However, matter from another planetary system is within reach since the identification of the first interstellar objects crossing the Solar System. First there was the now legendary 'Oumuamua which was reminiscent of the script for Arthur Clarke's novel Meeting with Rama and believed to have been born in the vicinity of a red dwarf. There is now the comet interstellar 2I / Borisov.

A mission is planned to attempt in the near future to observe these interstellar visitors more closely, and, why not, take samples of them. In the case of comet 67P / Tchourioumov-Guérassimenko, astrochemist, exobiologist and planetologist Olivier Poch, recently explained to us that his study was light news about the origin of thenitrogen on Earth, nitrogen that life uses crucially in the protein and theDNA. A mission to a cousin of 2I / Borisov could therefore prove to be very talkative on theexobiology and help us understand how rare life on Earth is in an galaxy, or not.

Swift, gamma-ray bursts to comets

In the meantime, the instruments with which the noosphere of the geochemist Vladimir Vernadsky and geologist and paleontologist Pierre Teilhard de Chardin, the collective spirit in a way Homo sapiens, Already allow us to probe the mysteries of the formation of planetary systems and chemistry prebiotic that they would host by diving into the composition of the coma by 2I / Borisov. This has been the case in recent months with the telescope Hubble, the network of radio telescope Alma and we learn it now via a publication of an article in The Astrophysical Journal and which can be viewed online at arXiv, with the Neil Gehrels observatory Swift of the Nasa.

As the ehealth below recalls, Swift was developed to study bursts gamma, some of the brightest explosions in the worldUniverse. But it turned out later that the instruments which equipped this NASA satellite, and in particular its ultraviolet / optical telescope (Uvot), could be used in other fields of theastrophysics. The American planetologist Dennis Bodewits Auburn University in Alabama has used it for several years to study comets.

With his colleagues, including Zexi Xing for a thesis at Auburn University, he therefore obtained telescope time with Swift to take several shots in ultraviolet by 2I / Borisov. The researchers were in particular on the trace of the hydroxyl radicals OH, products of the photodissociation of molecules of water degassed from the comet by the ultraviolet radiation of the Sun. Recall that according to the famous model of the “dirty snowball” proposed by theastronomer Fred Whipple in the early 1950s, comets are small frozen celestial bodies containing primordial matter dating from the earliest times of the formation of a planetary system. In the case of the Solar System, hundreds of billions would be “in the freezer” in the kuiper belt and the Oort cloud billions of kilometers from the Sun.

230 million liters of degassed extrasolar water

As a comet, 2I / Borisov also had to contain water ice, but also in a smaller amount of carbon dioxide (CO₂). Recently, Hubble also detected the atypical amount of carbon monoxide (CO) in the hair of the comet on the occasion of its degassing under the effect of the hot radiation of the Sun, in particular closer to our star. By combining all the observations, we finally arrive today at a first portrait of 2I / Borisov that summarizes a statement by Zexi Xing: “Borisov does not integrate perfectly into any class of comets in the Solar System, but it is not exceptionally distinguished from them. There are known comets that share at least one of its properties ”.

Swift made it possible to follow the loss of water from the comet which had started at its approach at 370 million kilometers from the Sun while 2I / Borisov was sinking at approximately 161,000 kilometers per hour on a orbit hyperbolic without return through the Solar System. The astrophysicists saw a 50% increase in the amount of hydroxyl – and therefore water – produced by Borisov between 1^er November and 1^er December, only seven days before his visit to perihelion. At the peak of its degassing, the water loss amounted to 30 liters per second. Cumulated over its entire time of activity, the comet would have released into the Solar System the equivalent of 230 million liters of water extrasolar. However as it moved away from the Sun, Borisov's water loss dropped faster than any previously observed comet. For Zexi Xing, this could have been caused by a variety of factors like a change in comet rotation and even its fragmentation which was highlighted in late March.

The fact remains that the loss of water made it possible to specify the size of the comet which is estimated to be around 0.74 km. On the other hand, it is at least 55% of its surface which sublimated under the action of the Sun's rays, which is 10 times the surface involved in the majority of the comets of the Solar System. Borisov nevertheless partially resembles them from a chemical point of view because Uvot has made it possible to identify molecules like C2 and amidogen in approximately 25% to 30% of all comets in the Solar System.