American physicists have found out what would happen to the Earth's atmosphere if it orbited the star Proxima Centauri in approximately the same orbit as the exoplanet Proxima b. According to the authors' estimates, the rate of atmospheric loss under conditions of strong ultraviolet radiation and high activity of Proxima will be at least 10 thousand times higher than that of the real Earth. With different initial data, the complete disappearance of the atmosphere will occur in a period of 100 million to 2 billion years, which is much less than the lifetime of Proxima b. The study was published in The Astrophysical Journal Letters, briefly reported in a NASA press release.
The existence of a terrestrial exoplanet near the closest star to the Sun - Proxima Centauri - became known a year ago. The Pale Red Dot project, after a long series of observations, unequivocally pointed to the fluctuations of the red dwarf associated with the gravity of the exoplanet located next to it. Moreover, according to the discoverers, Proxima b is located in the habitable zone of its star, which means that liquid water can exist on its surface.
However, some scientists have questioned the potential habitability of Proxima b. Proxima Centauri is a red dwarf, and its habitable zone is much closer to the star than, say, the Sun's habitable zone. At the same time, the activity of Proxima Centauri is associated with frequent flares and a large proportion of ultraviolet radiation, which can be detrimental to potential life on the exoplanet. The surface of Proxima b can be protected from these factors by a rather dense atmosphere comparable to that of the Earth - this was recently shown by the American physicist Dimitar Atri.
The authors of the new work tried to assess whether the existence of such a dense atmosphere at Proxima b is possible. In their models, physicists have placed the Earth - as a well-studied model object - in the orbit of an exoplanet and estimated the possible rate of decrease of its atmosphere. The main reason for this process would be the action of the star's hard ultraviolet radiation, the power of which is hundreds of times higher than the ultraviolet radiation in the vicinity of the real Earth.
The harsh ultraviolet light ionizes atmospheric gases by ripping electrons away from them. Following the negatively charged electrons, positively charged ions leave the atmosphere - this occurs most intensively near the magnetic poles. According to the authors' estimates, for the Earth's twin near Proxima Centauri, this process will occur 10 thousand times faster than for the Earth. This is equivalent to the fact that the total mass of the Earth's atmosphere will leave the planet in a time of about 100 million years, or, according to the most optimistic forecasts, about two billion years. This is much shorter than the lifetime of Proxima b.
Physicists note that such calculations do not completely rule out the suitability of Proxima b for life. But in order to preserve the atmosphere on an exoplanet, the mechanism of its occurrence must be very different from that of the earth.
Red dwarfs are the most common class of stars. Most of the discovered exoplanets orbit around such luminaries, and this attracts the attention of researchers looking for potentially habitable worlds. One of the most unusual of these systems is TRAPPIST-1, a red dwarf with seven exoplanets orbiting, four of which are in the habitable zone.
Vladimir Korolev
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