2023-09-27 14:46:45
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[EN VIDÉO] The planets of Trappist-1, astonishing worlds and perhaps rich in water Around this tiny star orbit seven planets the size of Earth. All…
Trappist-1 is a dwarf starred dwarf star — understand that it is cooler than our SunSun and only slightly larger than JupiterJupiter — located about 40 light years light years from Earth. It attracts a lot of attention because it is surrounded by at least seven planets. Earth-sized exoplanetsexoplanets. Enough to hope for finding habitable worlds. If not… inhabited!
Astronomers were impatiently waiting for the James Webb Space Telescope (JWST) to tell them a little more about these planets. Particularly on the two closest to Trappist-1. Scientists call them Trappist-1b and Trappist-1c. And by measuring their infrared emission, it should be possible to know if these exoplanets have an atmosphereatmosphere.
Atmosphere of Trappist-1b: beware of “ghost signals”
The first results published by astronomers in recent weeks described them as exoplanets probably devoid of atmosphere. Today, researchers from the University of Montreal (Canada) provide, in the journal Astrophysical Journal Letters, some details concerning Trappist-1b in particular. Thanks to spectroscopic observations carried out as the planet passed in front of its star. When light from a star passes through the atmosphere of one of its planets, it is imbued with a unique imprint. That of the atomsatoms and moleculesmolecules which make up this atmosphere.
The James-Webb telescope tells us more about this exoplanet as large as Earth
And it is precisely on this point that the work of researchers at the University of Montreal is important. They show that the activity of a star like Trappist-1 — red dwarfs have many spots and are shaken by numerous and violent eruptions — can generate kinds of “ghost signals”. Observations which misleadingly suggest the detection of a particular molecule in the atmosphere of an exoplanet. “We need to take this into account to correctly interpret the data returned by the James-Webb Space TelescopeJames-Webb Space Telescope”underlines Olivia Lim, main author of the study, in a press release from the University of Montreal.
No dense atmosphere for Trappist-1b
The researchers therefore integrated into their data a factor that they call “stellar contamination”. Enough to allow them to exclude certain types of atmosphere for Trappist-1b. With high confidence, they argue that atmospheres without clouds and hydrogen-rich hydrogen, for example, are not compatible with their data. The researchers thus confirm the results (see the article below) published last March: there does not seem to be a clear and extensive atmosphere around Trappist-1b. They also show how efficient and sensitive the NIRISSNIRISS instrument is when it focuses on the study of planetary atmospheres.
No significant atmosphere, therefore, for Trappist-1b. But why not a finer atmosphere? A bit like the one that surrounds a satellite of SaturnSaturn, TitanTitan, the only moon in our Solar System to have its own atmosphere. An atmosphere composed of water (H2O), carbon dioxidecarbon dioxide (CO2) and methane (CH4). Data from the James-Webb space telescope cannot yet rule it out. More observations will still be needed to find out.
Is the Trappist-1b exoplanet a habitable Earth 2.0? The James-Webb telescope has the answer
It belongs to one of the most promising star systems for the search for extraterrestrial life: the exoplanet Trappist-1b was probed by the MiriMiri instrument of the James-Webb telescope, in search of an atmosphere. What do these collected data tell us?
Article by Léa Fournissons published on 03/28/2023
Located 40.5 light years from Earth, the star Trappist-1 has intrigued astronomers since its discovery in 1999. Indeed, this red dwarf star is home to at least seven exoplanets, all of which have characteristics similar to rocky planetsrocky planets of our Solar SystemSolar system: size, massmass, or even density! Among them, three are in the habitable zone, the one which would allow the presence of water in the liquidliquid state.
This is why one of the first missions of the James-Webb telescope was to focus on it, and to point its Miri instrument towards this intriguing planetary system. He thus pointed his viewfinder towards Trappist-1b, the exoplanet closest to the star. The results have just been published in Nature. “These observations really take advantage of Webb’s mid-infrared capability”details Thomas Greene in a ESA communiquéan astrophysicist at NASA’s Ames Research Center and lead author of the study. “No previous telescope had the sensitivity to measure such faint mid-infrared light.”
Trappist-1b has no significant atmosphere
With a diameter similar to that of the Earth, Trappist-1b is however located much closer to its star, with a distance to its star 10 times less than that between MercuryMercury and the Sun. But, due to its star, a red dwarf whose radiation is much lower than that of the Sun, a yellow dwarf, the light it receives is substantially similar, equivalent to 4 times that of the Earth. Above all, “this planet is tidally locked, with one side facing the star at all times and the other in permanent darknessexplains Pierre-Olivier Lagage of the CEA, co-author of the article. If there is an atmosphere to circulate and redistribute the heat, the day side will be cooler than if there is no atmosphere.
This is precisely what the scientists were looking for: using a technique called secondary eclipse spectroscopy, they were able to measure the change in brightnessbrightness of the system when the planet passes behind the star. Then, it is possible to return to the brightness of the planet by subtracting the measurement during the eclipse from that without an eclipse. All in the infrared thanks to the Miri instrument from James-Webb, which corresponds to thermal radiationthermal radiation. This luminosity can then be linked to the temperature of the planet, therefore to the presence – or not – of an atmosphere!
The results are rather disappointing: there are none! “We compared the results to computer models showing what the temperature should be in different scenariosexplains Elsa Ducrot, scientist at the CEA and co-author of the study. The results are almost perfectly consistent with a blackbody consisting of bare rock and no atmosphere to circulate heat. We also did not see any signs of light absorption by carbon dioxide, which would be apparent in these measurements.”
“A truly important milestone in the history of exoplanet discovery”
If this result is not positive, it does however confirm James-Webb’s abilities, and remains very encouraging for the future. Because, for the very first time, a temperate exoplanet has been characterized. “There was a target that I dreamed of havingadd P. Luggage. And it was this one. This is the first time we can detect the emission from a rocky, temperate planet. This is a truly important milestone in the history of exoplanet discovery.”
Subsequently, other planets in the Trappist-1 system, or even other planetary systems, will be probed in the same way. Particularly around red dwarfs, the most likely stars for detecting extraterrestrial life. “There are ten times more of these stars in the Milky WayMilky Way than there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sunconclut T. P. Greene. But they’re also very active — they’re very bright when they’re young and they emit flares and X-rays that can wipe out an atmosphere.”
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