The dayside of TRAPPIST-1b, the innermost planet in the seven-planet system TRAPPIST-1, has a temperature of about 227 degrees Celsius (441 degrees Fahrenheit),according to an analysis of data from the Mid-Infrared Instrument (MIRI) onboard the NASA/ESA/CSA James Webb Space Telescope.
The TRAPPIST-1 system is remarkable for its seven planets that are similar in size, mass, density, and stellar heating to the rocky planets Venus, Earth, and Mars in our own Solar System. This illustration shows what the rocky planet TRAPPIST-1b could look like based on the new study. Image credit: NASA / ESA / CSA / J. Olmsted, STScI.
TRAPPIST-1 is an ultracool M-dwarf star located 38.8 light-years away in the constellation of Aquarius.
Also known as K2-112 or TIC 278892590, the star is barely larger than Jupiter and has just 8% of our Sun’s mass.
In February 2017, astronomers announced that the star hosts at least seven planets: TRAPPIST-1b, c, d, e, f, g and h.
All these planets are similar in size to Earth and Venus, or slightly smaller, and have very short orbital periods: 1.51, 2.42, 4.04, 6.06, 9.21, 12.35 and 20 days, respectively.
Three of these planets lay in the star’s habitable zone, meaning they may harbor suitable conditions for life.
TRAPPIST-1b, the innermost planet, has an orbital distance about one hundredth that of Earth’s and receives about four times the amount of energy that Earth gets from the Sun.
Although it is not within the habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other red-dwarf systems.
“There are 10 times as many of these stars in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” said Dr. Thomas Greene, an astrophysicist at NASA’s Ames Research Center.
“But they are also very active — they are very bright when they’re young, and they give off flares and X-rays that can wipe out an atmosphere.”
“It’s easier to characterize terrestrial planets around smaller, cooler stars,” said Dr. Elsa Ducrot, a researcher at the Université Paris-Saclay.
“If we want to understand habitability around M-dwarf stars, the TRAPPIST-1 system is a great laboratory. These are the best targets we have for looking at the atmospheres of rocky planets.”
This graphic compares the dayside temperature of TRAPPIST-1b as measured using Webb’s Mid-Infrared Instrument (MIRI) to computer models of what the temperature would be under various conditions. Image credit: NASA / ESA / CSA / J. Olmsted, STScI / Thomas Greene, NASA’s Ames Research Center / Taylor Bell, BAERI / Elsa Ducrot, CEA / Pierre-Olivier Lagage, CEA.
Previous observations of TRAPPIST-1b with the NASA/ESA Hubble and NASA’s Spitzer space telescopes found no evidence for a puffy atmosphere, but were not able to rule out a dense one.
One way to reduce the uncertainty is to measure the planet’s temperature.
“This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Dr. Pierre-Olivier Lagage, an astronomer at the Université Paris-Saclay.
“If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”
Using a technique called secondary eclipse photometry, the astronomers measured the change in brightness from the TRAPPIST-1 system as TRAPPIST-1b moved behind the star.
Although TRAPPIST-1b is not hot enough to give off its own visible light, it does have an infrared glow.
By subtracting the brightness of the star on its own (during the secondary eclipse) from the brightness of the star and planet combined, they were able to successfully calculate how much infrared light is being given off by the planet.
“There was one target that I dreamed of having,” Dr. Lagage said.
“And it was this one. This is the first time we can detect the emission from a rocky, temperate planet.”
“It’s a really important step in the story of discovering exoplanets.”
The study appears this week in the journal Nature.
T.P. Greene et al. Thermal Emission from the Earth-sized Exoplanet TRAPPIST-1 b using JWST. Nature, published online March 27, 2023; doi: 10.1038/s41586-023-05951-7
Source : Breaking Science News