Astronomers are announcing a newly discovered exoplanet in the habitable zone of its star, and another one — in the same system — that’s just twice the size of Earth. The Gliese 581 planetary system now has four known planets, with masses of about 1.9 (planet e, left in the foreground), 16 (planet b, nearest … Continue reading "Nearly Earth-sized Planet, Possible Watery World Spotted Near Another Star"