\u201cThese observations really take advantage of Webb\u2019s mid-infrared capability,\u201d said Thomas Greene, an astrophysicist at NASA\u2019s Ames Research Center and lead author on the study<\/a> published today in the journal Nature<\/em>. \u201cNo previous telescopes have had the sensitivity to measure such dim mid-infrared light.\u201d<\/p>\n\n\n\n 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 \u00ad\u2013 all could fit comfortably within the orbit of Mercury \u00ad\u2013 they receive comparable amounts of energy from their tiny star.<\/p>\n\n\n\n TRAPPIST-1 b, the innermost planet, has an orbital distance about one hundredth that of Earth\u2019s and receives about four times the amount of energy that Earth gets from the Sun. Although it is not within the system\u2019s habitable zone, observations of the planet can provide important information about its sibling planets, as well as those of other M-dwarf systems. <\/p>\n\n\n\n \u201cThere 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,\u201d explained Greene. \u201cBut they are also very active \u00ad\u2013 they are very bright when they\u2019re young, and they give off flares and X-rays that can wipe out an atmosphere.\u201d<\/p>\n\n\n\n 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, \u201cIt’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.\u201d<\/p>\n\n\n\n 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.<\/p>\n\n\n\n One way to reduce the uncertainty is to measure the planet\u2019s temperature. \u201cThis planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,\u201d said Pierre-Olivier Lagage from CEA, a co-author on the paper. \u201cIf it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.\u201d<\/p>\n\n\n\n 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.<\/p>\n\n\n\n Webb\u2019s 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%.<\/p>\n\n\n\n \u201cThere was also some fear that we\u2019d miss the eclipse. The planets all tug on each other, so the orbits are not perfect,\u201d said Taylor Bell, the post-doctoral researcher at the Bay Area Environmental Research Institute who analyzed the data. \u201cBut it was just amazing: The time of the eclipse that we saw in the data matched the predicted time within a couple of minutes.\u201d<\/p>\n\n\n\n The team analyzed data from five separate secondary eclipse observations. \u201cWe compared the results to computer models showing what the temperature should be in different scenarios,\u201d explained Ducrot. \u201cThe results are almost perfectly consistent with a blackbody made of bare rock and no atmosphere to circulate the heat. We also didn\u2019t see any signs of light being absorbed by carbon dioxide, which would be apparent in these measurements.\u201d<\/p>\n\n\n\n This research was conducted as part of Webb Guaranteed Time Observation (GTO) program 1177<\/a>, which is one of eight programs from Webb\u2019s 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<\/a> 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.<\/p>\n\n\n\n \u201cThere was one target that I dreamed of having,\u201d said Lagage, who worked on the development of the MIRI instrument for more than two decades. \u201cAnd it was this one. This is the first time we can detect the emission from a rocky, temperate planet. It\u2019s a really important step in the story of discovering exoplanets.\u201d<\/p>\n\n\n\n We recommend you: Hubble Monitors Changing Weather and Seasons at Jupiter and Uranus<\/a><\/p>\n\n\n\n![\"Infographic](\"https:\/\/www.nasa.gov\/sites\/default\/files\/styles\/full_width\/public\/thumbnails\/image\/stsci-01gw5g2m4kydk1s2t56nknmgk7.jpg?itok=mBaFiEUx\" "\\"\\"\/")
<\/a><\/figure>\n\n\n\nRocky Planets Orbiting Ultracool Red Dwarfs<\/h2>\n\n\n\n
Detecting an Atmosphere (or Not)<\/h2>\n\n\n\n
![\"Infographic](\"https:\/\/www.nasa.gov\/sites\/default\/files\/styles\/full_width\/public\/thumbnails\/image\/stsci-01gw5ft7gxb5bkx2jz45m8hgrm.jpg?itok=ycYl0m-O\" "\\"\\"\/")
<\/a><\/figure>\n\n\n\nMeasuring Minuscule Changes in Brightness<\/h2>\n\n\n\n