Just 40 light-years from Earth, the TRAPPIST-1 system of planets is home to the largest family of Earth-like worlds known to astronomers. At least seven planets are known to orbit within the TRAPPIST-1 solar system. A new study shows these worlds have nearly identical densities — within just a few percent of each other. This suggests that each of these seven planets could have similar compositions. “This is one of the most precise characterizations of a set of rocky exoplanets, which gave us high-confidence measurements of their diameters, densities, and masses. This is the information we needed to make hypotheses…

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