2023-05-08 09:05:34
The great exobiologist Carl Sagan understood that the discovery of life elsewhere than on Earth, and much more of intelligent life technologically at least as advanced as us, would have major philosophical and societal implications. It would already be an important discovery in this respect if we might at least determine to what extent the Earth and its biospherebiosphere are rare or not in the Milky WayMilky Way. During the interview he granted to Futura, Jean-Pierre Bibring put forward the thesis that, according to him, the Earth and life were a product of so many contingent events depending on particular local conditions that one might ‘expect to never find’exoterreexoterre in the Milky Way and perhaps far beyond as well.
The question is still largely open and exobiologists are working to get an answer. For example, they seek to determine the habitability of exoplanetsexoplanets rocky in orbitorbit around the red dwarfsred dwarfs. They are indeed the most numerous stars of the GalaxyGalaxy. But one wonders if they are favorable to life.
Explanations by Franck Selsis, astrophysicist, LAB, University of Bordeaux. The light of a star: the best and the worst thing for life! ” Born under a lucky star », third stage of the AstrobioEducation journey. Throughout this video you will hear regarding the Tatooine planets, inspired by the universe Star Wars, and you will know if they can potentially be habitable. © French Society of Exobiology
A super-Earth sterilized by a red dwarf?
the red dwarfs being less luminous and colder than the SoleilSoleilthe habitable zonehabitable zone naive that would allow the average surface temperature of a rocky exoplanet orbiting these stars to be consistent with water liquidliquid is much closer tostarstar host than in the case of Solar systemSolar system. However, the red dwarfs are very angry at the beginning of their long existence, producing important floods of X-raysX-rays et ultravioletultraviolet. The question then arises as to whether rocky exoplanets in this area can retain enough water and a atmosphereatmosphere protection to allow life to thrive, the water molecules being able to be photo-dissociated by these radiations and the atmosphere sometimes being able, as was the case of Mars but not of VenusVenusbe totally eroded by the ventsvents and stellar flares.
There is only one way to advance towards the solution of these questions, to study rocky exoplanets near red dwarfs, knowing in particular that the existence of certain atmospheres makes it possible to have a more complex notion of what the we must wait for conditions making an exoplanet habitable.
A group of astrophysicists has just used the instruments of the James-Webb telescope (JWSTJWST) to observe using the spectrographespectrographe close infraredinfrared from Webb (NIRSpecNIRSpec) la superTerre GJ 486 b. It is not in the naïve habitability zone because orbiting in just under 1.5 Earth days around GJ 486, its average surface temperature must be around 430°C.
These researchers used transitstransits for regarding an hour each to try to highlight the presence of water vapor in a possible atmosphere. GJ 486 b is regarding 30% larger than Earth and three times as massive, which means it is a rocky world with a gravitygravity stronger than on our Blue Planet, perhaps strong enough to retain an atmosphere with water vapour.
As explained in the article published in The Astrophysical Journal Letters and freely available on arXiv, astrophysicists have effectively highlighted this water vapor near the superTerresuperTerreor at least its presence is suggested by three different analytical methods coupled with modelingmodeling astrochemicals of a possible atmosphere.
Water vapor produced by stellar spots?
But, as also explained in a press release from NASA, one of the authors of the discovery, Kevin Stevenson of the laboratory of physiquephysique applied from Johns-Hopkins University in Laurel, Maryland, water vapor in the atmosphere of a rocky planetrocky planet warm would represent a major breakthrough for the science of exoplanets. But we have to be careful and make sure the star isn’t the culprit “. His colleague Sarah Moran, from the University of Arizona in Tucson, also in the United States, adds: We see a signal, and it’s almost certainly due to water. But we can’t yet tell if this water is part of the planet’s atmosphere, which means the planet has an atmosphere, or if we just see a water signature coming from the star. »
Paradoxically, the atmosphere of a red dwarf, already less hot than in the case of the Sun, can also be locally cold enough at the level of the equivalents of sunspots to allow the formation of water molecules in the form of vapour. The researchers concede however that they do not see any trace of these spots in the curve of lightlight transits obtained (which is the case for certain stars with exoplanets).
Observations at shorter infrared wavelengths by another JWST instrument, the Near Infrared Imager and Slitless Spectrograph (NirissNiriss), will be necessary to decide between the scenarios with planetary atmosphere or stellar spots.
But if an atmosphere with water vapor is indeed present on GJ 486 b, it will probably be necessary to conclude that it is still constantly supplied with water by volcanic eruptionsvolcanic eruptionsbecause the activity of the red dwarf must all the same contribute to erode this atmosphere.
Is the Earth an ordinary world? Are all exoplanetary systems like ours? How is a habitable planet built? Another video from the AstrobioEducation educational journey. © French Society of Exobiology
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