Webb measures the temperature of a rocky exoplanet

Use an international team of researchers James Webb Space Telescope NASA measures the temperature of the rocky exoplanet TRAPPIST-1b

This is the first detection of any form of light emanating from a small, cold exoplanet. Like the rocky planets in our solar system. The result represents an important step in determining whether planets orbit small, active stars such as TRAPPIST-1 They can support the atmosphere needed to support life. It also bodes well for Webb’s ability to characterize temperate, Earth-sized exoplanets using MIRI.

“These feedback really take advantage of Webb’s mid-infrared capability.“, He said Thomas Greenan astrophysicist at NASA Ames Research Center and lead author of the study published today in the journal nature. “No previous telescope had the sensitivity to measure faint infrared light.“.

Rocky planets orbit ultra-cool red dwarfs

In early 2017, astronomers reported a discovery Seven rocky planets orbiting a very cold red dwarf star (or M dwarf) 40 light years from Earth. What distinguishes the planets is their similarity in size and mass to the rocky inner planets in our solar system.. Although they all orbit much closer to their star than any of our planets that orbit the sun, they could all fit comfortably within the orbit of Mercury.

TRAPPIST-1 b, the innermost planetIt has an orbital distance of about one-hundredth from Earth and receives about four times the amount of energy Earth gets from the Sun. Although not within the system’s habitable zone, observations of the planet can provide important information about its sister planets, as well as other planets of M dwarf systems.

“There are ten times more of these stars in the Milky Way than stars like the Sun, and they are twice as likely to have rocky planets as there are stars like the Sun.Green explained.But they are also very active: they are very bright when young and emit flares and X-rays that can destroy the atmosphere.“.

Co-author Elsa Ducrot from the French Commission for Alternative Energies and Atomic Energy (CEA) in France, which was part of the team that conducted the previous studies of the TRAPPIST-1 system, added: “Terrestrial planets around smaller, cooler stars are easy to characterize. “If we want to understand the habitability around M stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”“.

Atmospheric detection (or not)

previous notes TRAPPIST-1b With the Hubble and Spitzer Space Telescopes They found no evidence of a distended atmospherebut they could not rule out dense.

One way to reduce uncertainty is to measure the planet’s temperature. “This planet is phase-locked, with one side facing the star at all times and the other in perpetual darkness.said Pierre-Olivier Lagage of CEA, a co-author of the research. “If you have an atmosphere to circulate and redistribute heat, the side of the day will be cooler than if there was no atmosphere.“.

The team used a file A technique called secondary eclipse photometry, where MIRI measured the change in the system’s brightness as the planet moved behind the star. Although TRAPPIST-1 b is not hot enough to emit its own visible light, it does glow in infrared. By subtracting the star’s brightness alone (during a secondary eclipse) from the combined brightness of the star and planet, they were able to successfully calculate how much infrared light the planet was emitting.

Measure subtle changes in luminosity

Web’s discovery of the secondary eclipse itself is a major milestone.. Since the star is 1,000 times brighter than the planet, the change in brightness is less than 0.1%.

“There was also some fear that we might miss the eclipse. All planets attract each other, so the orbits are not perfect.“, He said Taylor Bell, a postdoctoral researcher at the Bay Area Environmental Research Institute who analyzed the data. “But it was amazing: the eclipse time we saw in the data matched the predicted time within two minutes.“.

The team analyzed data from five separate secondary observations of the eclipse. “We compared the results to computer models that show what the temperature should be under different scenarios.Ducrot explained. “The results are almost perfectly consistent with a black body made of bare rock and no atmosphere to distribute heat. We also saw no signs of CO2 absorbing light, which would be evident in these measurements.“.

This research was conducted as part of the 1177’s Program Web-Guaranteed Time Monitoring (GTO), which is one of eight first-year Webb science programs designed to help fully characterize the TRAPPIST-1 system. Additional observations of TRAPPIST-1 b’s secondary eclipse are currently underway, and now that they know how good the data is, the team hopes to finally capture a complete phase curve that shows the change in brightness over the entire orbit. This will allow them to see how the temperature changes from day to night and confirm whether or not the planet has an atmosphere.

“There was a goal that I dreamed of achievingsaid Lagage, who has worked on developing the MIRI tool for more than two decades. “And that was it. It’s the first time we can detect emissions from a rocky, temperate planet. This is a really important step in the history of exoplanet discovery.“.

March 27, 2023

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