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Earth-Sized Worlds of TRAPPIST-1

28 May 2016, 22:00 UTC
Earth-Sized Worlds of TRAPPIST-1
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Figure 1: Artist's impression of a planet orbiting a red dwarf star.TRAPPIST-1 is an M8.0 ± 0.5 type red dwarf star located about 40 light years away. It has only ~1/2000th the Sun's luminosity, ~8 percent the Sun's mass, ~11.5 percent the Sun's radius, and its effective temperature is only 2550 ± 55K. For comparison, the Sun's effective temperature is 5778 K. TRAPPIST-1 is slightly larger in size than the planet Jupiter and its low effective temperature classifies it as an ultracool dwarf. Ultracool dwarfs are a class of stellar-like objects with effective temperatures below 2700 K. They include extremely low mass red dwarf stars and brown dwarfs.Observations of TRAPPIST-1 revealed the presence of three transiting Earth-size planets in orbit around it. The three planets are identified as TRAPPIST-1b, TRAPPIST-1c and TRAPPIST-1d. The two inner planets, TRAPPIST-1b and TRAPPIST-1c, orbit interior to the habitable zone around the star. Nevertheless, both planets are expected to be tidally-locked, with a permanent day-side hemisphere and a permanent night-side hemisphere. As a result, they can still support habitable regions, especially in the temperate regions around the day-night terminator. For TRAPPIST-1d, there are a number of solutions that place it within or beyond the habitable ...

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