From left to right, John M. Grunsfeld, Associate Administrator for the Science Mission Directorate at NASA, Jim Green, director of planetary science at NASA, and Michael Meyer, lead scientist for the Mars Exploration Program at NASA Headquarters, announce that NASA has confirmed that liquid water flows on the surface of Mars, during a press conference at NASA headquarters in Washington, D.C. on September 28, 2015. Photo by Kevin Dietsch/UPI