Telescopes show Earth's sister planet swelling to an apparent diameter wider than Jupiter, while its phase thins dramatically from 37% to 15% lit. Soon after sunset on Feb. 1, direct your ...

"There are still many things related to planetary formation and the early evolution of young planetary systems that we don't understand." The discovery of an extraordinary multi-planet system has ...

Because Io is so close to its massive host planet, the moon is subjected to a tremendous gravitational pull as it orbits Jupiter once about every 42 hours, according to the Planetary Society.