TRAPPIST-1 is a red dwarf star approximately 40 light years from here. Small and dim, it was only discovered in 1999 as part of an infrared sky survey. In the last few years, it has been established to have a system of terrestrial (roughly Earth-sized) planets orbiting it. The planets are mostly close to the star and to each other, with significant gravitational interactions amongst them bringing most of their orbits into near-resonance.

 Now, we have new data on the makeup of these planets. In an open access paper in The Planetary Science Journal, a team using the Spitzer Space Telescope. All of the planets seem to have very similar densities, suggesting they likely formed together and have similar compositions. It also appears they all have little or no water, despite some being located in the theoretically habitable zone of the star – a potential blow to suggestions that these worlds could harbor complex life, but presenting other interesting questions about the worlds’ formation and evoltuion.


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