MSGID: 1:317/3 64226d5f   
   PID: hpt/lnx 1.9.0-cur 2019-01-08   
   TID: hpt/lnx 1.9.0-cur 2019-01-08   
    Temperature of a rocky exoplanet measured    
      
     Date:   
         March 27, 2023   
     Source:   
         NASA/Goddard Space Flight Center   
     Summary:   
         An international team of researchers has used NASA's James Webb   
         Space Telescope to measure the temperature of the rocky exoplanet   
         TRAPPIST-1 b.   
      
         The measurement is based on the planet's thermal emission: heat   
         energy given off in the form of infrared light detected by Webb's   
         Mid-Infrared Instrument (MIRI). The result indicates that the   
         planet's dayside has a temperature of about 500 kelvins (roughly   
         450 degrees Fahrenheit) and suggests that it has no significant   
         atmosphere.   
      
      
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   FULL STORY   
   ==========================================================================   
   An international team of researchers has used NASA's James Webb Space   
   Telescope to measure the temperature of the rocky exoplanet TRAPPIST-1   
   b. The measurement is based on the planet's thermal emission: heat energy   
   given off in the form of infrared light detected by Webb's Mid-Infrared   
   Instrument (MIRI). The result indicates that the planet's dayside has   
   a temperature of about 500 kelvins (roughly 450 degrees Fahrenheit)   
   and suggests that it has no significant atmosphere.   
      
      
   ==========================================================================   
   This is the first detection of any form of light emitted by an exoplanet   
   as small and as cool as the rocky planets in our own solar system. The   
   result marks an important step in determining whether planets orbiting   
   small active stars like TRAPPIST-1 can sustain atmospheres needed to   
   support life. It also bodes well for Webb's ability to characterize   
   temperate, Earth-sized exoplanets using MIRI.   
      
   "These observations really take advantage of Webb's mid-infrared   
   capability," said Thomas Greene, an astrophysicist at NASA's Ames   
   Research Center and lead author on the study published today in the   
   journal Nature. "No previous telescopes have had the sensitivity to   
   measure such dim mid-infrared light."  Rocky Planets Orbiting Ultracool   
   Red Dwarfs In early 2017, astronomers reported the discovery of seven   
   rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40   
   light-years from Earth.   
      
   What is remarkable about the planets is their similarity in size and mass   
   to the inner, rocky planets of our own solar system. Although they all   
   orbit much closer to their star than any of our planets orbit the Sun -   
   all could fit comfortably within the orbit of Mercury - they receive   
   comparable amounts of energy from their tiny star.   
      
   TRAPPIST-1 b, 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 system's habitable zone, observations of the planet can provide   
   important information about its sibling planets, as well as those of   
   other M-dwarf systems.   
      
   "There are ten 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," explained Greene. "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."  Co-author Elsa Ducrot from the   
   French Alternative Energies and Atomic Energy Commission (CEA) in France,   
   who was on the team that conducted earlier studies of the TRAPPIST-1   
   system, added, "It's easier to characterize terrestrial planets around   
   smaller, cooler stars. If we want to understand 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."   
   Detecting an Atmosphere (or Not) Previous observations of TRAPPIST-1   
   b with the Hubble and 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 Pierre-Olivier   
   Lagage from CEA, a co-author on the paper. "If it has an atmosphere to   
   circulate and redistribute the heat, the dayside will be cooler than   
   if there is no atmosphere."  The team used a technique called secondary   
   eclipse photometry, in which MIRI measured the change in brightness from   
   the system as the planet moved behind the star. Although TRAPPIST-1 b 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.   
      
   Measuring Minuscule Changes in Brightness Webb's detection of a secondary   
   eclipse is itself a major milestone. With the star more than 1,000 times   
   brighter than the planet, the change in brightness is less than 0.1%.   
      
   "There was also some fear that we'd miss the eclipse. The planets all   
   tug on each other, so the orbits are not perfect," said Taylor Bell,   
   the post-doctoral researcher at the Bay Area Environmental Research   
   Institute who analyzed the data. "But it was just amazing: The time of   
   the eclipse that we saw in the data matched the predicted time within   
   a couple of minutes."  The team analyzed data from five separate   
   secondary eclipse observations. "We compared the results to computer   
   models showing what the temperature should be in different scenarios,"   
   explained Ducrot. "The results are almost perfectly consistent with a   
   blackbody made of bare rock and no atmosphere to circulate the heat. We   
   also didn't see any signs of light being absorbed by carbon dioxide, which   
   would be apparent in these measurements."  This research was conducted   
   as part of Webb Guaranteed Time Observation (GTO) program 1177, which is   
   one of eight programs from Webb's first year of science designed to help   
   fully characterize the TRAPPIST-1 system. Additional secondary eclipse   
   observations of TRAPPIST-1 b are currently in progress, and now that they   
   know how good the data can be, the team hopes to eventually capture a full   
   phase curve showing the change in brightness over the entire orbit. This   
   will allow them to see how the temperature changes from the day to the   
   nightside and confirm if the planet has an atmosphere or not.   
      
   "There was one target that I dreamed of having," said Lagage, who worked   
   on the development of the MIRI instrument for more than two decades. "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."   
       * RELATED_TOPICS   
             o Space_&_Time   
                   # Extrasolar_Planets # Stars # Astronomy # Pluto #   
                   Kuiper_Belt # Eris_(Xena) # Mars # Sun   
       * RELATED_TERMS   
             o Spitzer_space_telescope o Space_observatory o   
             Compton_Gamma_Ray_Observatory o Eris_(dwarf_planet) o Uranus   
             o Titan_(moon) o Venus o Neptune   
      
   ==========================================================================   
   Story Source: Materials provided by   
   NASA/Goddard_Space_Flight_Center. Note: Content may be edited for style   
   and length.   
      
      
   ==========================================================================   
   Journal Reference:   
      1. Thomas P. Greene, Taylor J. Bell, Elsa Ducrot, Achre`ne Dyrek,   
      Pierre-   
         Olivier Lagage, Jonathan J. Fortney. Thermal Emission from the   
         Earth- sized Exoplanet TRAPPIST-1 b using JWST. Nature, 2023; DOI:   
         10.1038/ s41586-023-05951-7   
   ==========================================================================   
      
   Link to news story:   
   https://www.sciencedaily.com/releases/2023/03/230327163227.htm   
      
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