The sensitivity required to distinguish between various atmospheric scenarios on such a small planet so far away is truly remarkable. If the cooler, more temperate TRAPPIST-1 planets formed under similar conditions, they too may have started with little of the water and other components necessary to make a planet habitable. The absence of a thick atmosphere suggests that the planet may have formed with relatively little water. The data also shows that it is unlikely the planet is a true Venus analog with a thick CO2 atmosphere and sulfuric acid clouds. This is because the CO2 would be absorbing all of the 15-micron light, so we wouldn’t detect any coming from the planet.” “If the planet had a thick CO2 atmosphere, we would have observed a really shallow secondary eclipse, or none at all. “Our results are consistent with the planet being a bare rock with no atmosphere, or the planet having a really thin CO2 atmosphere (thinner than on Earth or even Mars) with no clouds,” said Zieba. (Because TRAPPIST-1 c orbits so close to its star – about 1/50th the distance between Venus and the Sun – it is thought to be tidally locked, with one side in perpetual daylight and the other in endless darkness.)Īlthough these initial measurements do not provide definitive information about the nature of TRAPPIST-1 c, they do help narrow down the likely possibilities. In addition, a substantial atmosphere of any composition will redistribute heat from the dayside to the nightside, causing the dayside temperature to be lower than it would be without an atmosphere. However, clouds can reflect light, making the planet appear brighter and masking the presence of carbon dioxide. Carbon dioxide gas preferentially absorbs 15-micron light, making the planet appear dimmer at that wavelength. The amount of mid-infrared light emitted by a planet is directly related to its temperature, which is in turn influenced by atmosphere. This method is the same as that used by another research team to determine that TRAPPIST-1 b, the innermost planet in the system, is probably devoid of any atmosphere. By comparing the brightness when the planet is behind the star (starlight only) to the brightness when the planet is beside the star (light from the star and planet combined) the team was able to calculate the amount of mid-infrared light with wavelengths of 15 microns given off by the dayside of the planet. To address these questions, the team used MIRI (Webb’s Mid-Infrared Instrument) to observe the TRAPPIST-1 system on four separate occasions as the planet moved behind the star, a phenomenon known as a secondary eclipse. In addition, there may or may not have been enough water, carbon dioxide, and other volatiles available to make substantial atmospheres when the planets formed. During the first billion years of their lives, M dwarfs emit bright X-ray and ultraviolet radiation that can easily strip away a young planetary atmosphere. Although the planets are similar in size and mass to the inner, rocky planets in our own solar system, it is not clear whether they do in fact have similar atmospheres. TRAPPIST-1 c is one of seven rocky planets orbiting an ultracool red dwarf star (or M dwarf) 40 light-years from Earth.
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