Another feat for the James Webb: the giant space telescope has managed to measure the temperature of a rocky “cousin” planet of Earth for the first time, located 40 light years from our solar system, according to a study published Monday in Nature.
Discovered in 2017, the Trappist-1 system has seven planets revolving around a small “cold” star, a red dwarf, half as hot as the Sun. This planetary system is a target of choice for the James Webb Telescope (JWST), developed by NASA and in service since July 2022, one of whose missions is to probe the atmosphere of potentially habitable exoplanets, beyond the system. solar.
TRAPPIST-1 b: We give it a one (M-dwarf) star review; it lacks atmosphere. ⭐
Webb found the dayside temperature of this rocky exoplanet to be about 450º F (227º C) — suggesting it has no significant atmosphere: https://t.co/TGYqguDgT4
Here’s why this is a big deal ⬇️ pic.twitter.com/7kW8nKxC4U
— NASA Webb Telescope (@NASAWebb) 27 mars 2023
Trappist-1 is an “excellent laboratory” for this quest, NASA points out in a press release: it is close to the solar system and contains only rocky planets, all of similar size and mass to Earth. But it is difficult to know their characteristics because exoplanets cannot be observed directly from such a great distance, unlike the stars around which they orbit. To detect them, astronomers use the transit method, which captures the variations in luminosity caused by the passage of the planet in front of its host star, like a micro-eclipse.
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Previously unexplored wavelengths
The JWST’s Mirim imager, capable of observing in the mid-infrared, was able to capture a so-called secondary eclipse, when the planet passes behind its star. In this case the planet Trappist -1b, the closest to the star Trappist-1 and therefore the easiest to study because its transits are more numerous. “It is just before disappearing behind the star that the planet adds the most light (to that of the star) because it almost exclusively shows its “day” side, explains to AFP Elsa Ducrot, astrophysicist at the Commissariat at Atomic Energy (CEA), co-author of the study.
By comparing the amount of light detected before and during the occultation, scientists deduce the part emitted by the planet. It is light detectable only in the mid-infrared, a wavelength hitherto unexploited by astronomers, which makes it possible to detect the thermal emission of the planet: the JWST acts “like a giant non-contact thermometer”, comments NASA, one of the astrophysicists, Thomas Greene, is the main author of the study.
Trappist-1b ‘has little or no atmosphere’
Trappist-1-b’s temperature measurement is a first for a rocky exoplanet. It is around 230 degrees Celsius there on the day side, suggesting “that there is no redistribution of heat over the whole planet, a role provided by an atmosphere”, specifies the CEA, which designed the imager Mirim.
Conclusion: Trappist-1b “has little or no atmosphere”, develops Elsa Ducrot, emphasizing that it will be necessary to search at other wavelengths to decide. What is certain, however, is that if there is an atmosphere, it does not contain carbon dioxide, continues the astrophysicist.
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As many details as a previous telescope, Spitzer, had failed to detect “despite the observation of 28 secondary eclipses of Trappist-1b”. “The James Webb saw them in a single eclipse!” Says the scientist. By revealing for the first time the atmosphere around a rocky planet, the telescope developed by NASA opens “a new era” for the study of exoplanets, she adds.
Trappist-1b is too close to its star to be likely to harbor life forms as we know it. But its observation can provide valuable information on its sister planets, abounds NASA. Including Trappist-1e, Trappist-1f and Trappist-1g which are in the habitable zone. A region neither too hot nor too cold to have liquid water, a condition conducive to extraterrestrial life.
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