The seven rocky worlds of TRAPPIST-1

NASA had a big announcement today: the dwarf star TRAPPIST-1 has at least seven terrestrial planets, and at least three of them are in the star’s “goldilocks zone”, where liquid water could exist on the surface (assuming sufficient atmospheric pressure).

TRAPPIST-1 got its name from a Belgian telescope called the Transiting Planets and Planetesimals Small Telescope, situated at La Silla Observatory in Chile’s Atacama Desert.  TRAPPIST found that the star (catalogue number 2MASS J23062928-0502285) had at least three exoplanets orbiting it by observing the star’s lightcurve change as the planets transited.

Subsequently, NASA’s Spitzer Space Telescope was called in to confirm the discovery, in a marathon 500-hour focused study of the TRAPPIST-1 system.  And it did!  Today, NASA announced that not only are the three worlds real, there are at least four more.  And at least three but possibly all of them are in the habitable zone.  This is the largest collection of terrestrial worlds ever found.  Since they orbit quite near their dim parent, astronomers were able to calculate their densities, and they’re pretty close in size to Earth — some are actually smaller.

The Hubble Space Telescope is now being called in to study the planets in more detail, and hopefully to determine whether or not any of them has a substantial atmosphere, preferably one with an unusual concentration of hydrogen, which would imply water vapor.  So far, it hasn’t found evidence of an atmosphere (and has largely ruled out the kind of atmosphere we’re all hoping for on TRAPPIST-1b and TRAPPIST-1c), but they’re still looking, and the search is expected to continue into the James Webb Space Telescope.  The hobbled Kepler Space Telescope (now “K2”) has also been studying this system.

Here’s an artist’s concept, to show you the relative sizes (note that color is completely imaginary at this point):

pia21428_-_trappist-1_comparison_to_solar_system_and_jovian_moons

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