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[EN VIDÉO] The planets of Trappist-1, amazing worlds and perhaps rich in water. Seven planets the size of Earth orbit around this tiny star. All…
Trappist-1 is a dwarf dwarf star – understand that it is cooler than our SunSun and only slightly larger than JupiterJupiter – and is 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 exoplanets, exoplanets. Enough to hope to find habitable worlds. If not… inhabited!
Astronomers waited impatiently for the James Webb Space Telescope (JWST) to tell them a little more about these planets. Especially 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 find out whether these exoplanets have an atmosphere.
Atmosphere of Trappist-1b: Beware of “ghost signals”
The first results published by astronomers in recent weeks described them as exoplanets that probably have no atmosphere. Today, researchers at the University of Montreal (Canada) provide some details about Trappist-1b in particular in the Astrophysical Journal Letters. Thanks to spectroscopic observations made as the planet passed in front of its star. When a star’s light penetrates the atmosphere of one of its planets, it leaves a unique imprint. That of the atoms, atoms and molecules that make up this atmosphere.
The James Webb Telescope tells us more about this Earth-sized exoplanet
And this is precisely where 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 rocked by numerous and violent eruptions – can produce types of “ghost signals.” Observations that incorrectly suggest the detection of only one particular molecule in an exoplanet’s atmosphere. “We need to take this into account in order to correctly interpret the data provided by the James Webb Space Telescope,” emphasizes Olivia Lim, lead author of the study, in a press release from the University of Montreal.
No dense atmosphere for Trappist-1b
The researchers therefore integrated a factor into their data that they call “star contamination”. Enough to rule out certain types of atmospheres for Trappist-1b. They argue with great conviction that, for example, atmospheres without clouds and hydrogen-rich hydrogen are not compatible with their data. The researchers thus confirm the results published last March (see article below): There does not seem to be a clear and comprehensive atmosphere around Trappist-1b. They also show how efficient and sensitive the NIRISSNIRISS instrument is when it focuses on studying planetary atmospheres.
Therefore no significant atmosphere for Trappist-1b. But why not a more refined atmosphere? A bit like the one that surrounds a satellite of SaturnSaturn, TitanTitan, the only moon in our solar system that has its own atmosphere. An atmosphere consisting of water (H2O), carbon dioxide carbon dioxide (CO2) and methane (CH4). Data from the James Webb Space Telescope cannot yet rule it out. Further observations are required to find out.
Is the exoplanet Trappist-1b a habitable Earth 2.0? The James Webb Telescope has the answer
It is one of the most promising star systems for the search for extraterrestrial life: The exoplanet Trappist-1b was examined by the MiriMiri instrument of the James Webb Telescope in search of an atmosphere. What does this collected data tell us?
Article by Léa Fournissons published on March 28, 2023
Located 40.5 light-years from Earth, the star Trappist-1 has fascinated astronomers since its discovery in 1999. In fact, this red dwarf star is home to at least seven exoplanets, all of which have similar characteristics to rocky planets of our solar system: size, mass, mass or even density! Three of them are in the habitable zone, the one that would allow the existence of water in its liquid state.
That’s why one of the James Webb Telescope’s first missions was to focus on and point its Miri instrument at this fascinating planetary system. So he pointed his viewfinder at Trappist-1b, the closest exoplanet to the star. The results have just been published in Nature. “These observations really take advantage of Webb’s mid-infrared capability,” explains Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author of the study, in an ESA press release. “No previous telescope had the sensitivity to measure such faint light in the mid-infrared.”
Trappist-1b has no atmosphere to speak of
However, with a diameter similar to Earth’s, Trappist-1b is much closer to its star, and the distance to its star is ten times less than that between Mercury 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 essentially similar, namely four times that of Earth. Above all, “this planet is tidally locked, with one side always facing the star and the other in constant darkness,” explains Pierre-Olivier Lagage of the CEA, co-author of the paper. When there is an atmosphere that can circulate and redistribute heat, the dayside is cooler than without an atmosphere.
That’s exactly what the scientists were looking for: using a technique called secondary eclipse spectroscopy, they could measure the change in brightness of the system as 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 the measurement without the eclipse. All in the infrared range thanks to James-Webb’s Miri instrument, which corresponds to thermal radiation. This luminosity can then be linked to the temperature of the planet, i.e. to the presence – or absence – of an atmosphere!
The results are rather disappointing: there are none! “We compared the results with computer models that showed what the temperature should be in different scenarios,” explains Elsa Ducrot, a scientist at the CEA and co-author of the study. The results are almost entirely consistent with a black body consisting of bare rock with no atmosphere for heat circulation. We also saw no evidence of light absorption by carbon dioxide that would be evident in these measurements.”
“A truly important milestone in the history of exoplanet discovery”
Although this result is not positive, it confirms James-Webb’s abilities and remains very encouraging for the future. For the first time ever, a temperate exoplanet has been characterized. “There was a goal that I dreamed of,” adds Fr. Lagage. And it was this one. This is the first time we have detected emission from a rocky, temperate planet. This is a really important milestone in the history of exoplanet discovery.”
Other planets in the Trappist-1 system or even other planetary systems will then be examined in the same way. Especially near red dwarfs, the most likely stars for discovering extraterrestrial life. “There are ten times more of these stars in the Milky Way than there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” concludes TP Greene. But they are also very active – they are very bright when they are young, and they emit flares and X-rays that can blot out the atmosphere.”