“We don't know how many planets we're going to have to examine before we find life, and not finding it on 10 or 100 doesn't mean it's not there. This may be very tricky.”

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.