“Because of Hubble and other telescopes, we've now discovered that there are probably planets around every star, or virtually every star. There are solar systems around most stars. And the fact that we're here on a planet, Earth, means that it's likely there's lots of other Earths out there.”

American physicist and former NASA astronaut

John Mace Grunsfeld is an American physicist and former NASA astronaut. Born in 1958, he is known for five Space Shuttle flights, for serving as NASA chief scientist, and for later leadership roles in NASA science. His work has ranged across high-energy astrophysics, cosmic ray physics, and early exoplanet research, with an interest in the instruments that will support future astronomy. After leaving NASA in 2009, he became deputy director of the Space Telescope Science Institute in Baltimore, then returned to NASA in 2012 as associate administrator of the Science Mission Directorate before retiring again in 2016.