Meet Kepler-138b, a Mars-sized planet with the smallest measured mass

You've heard of hot Jupiters, mini-Neptunes and super-Earths -- but how about an almost-Mars? Scientists using data from NASA's Kepler spacecraft have pinned down the mass of an exoplanet that's slightly lighter than the Red Planet -- making it the smallest such world to have its density measured.

via L.A. Times - Science http://ift.tt/1SqgCeo