An ancient river is helping NASA's Perseverance Mars rover do its work

NASA's Perseverance Mars rover sealed the tube containing its 20th rock core sample on June 23 (the 832nd Martian day, or sol, of the mission), and the mission's science team is excited about its potential. That's because this sample was drilled by the rover from an outcrop composed of tiny chunks of other rocks that were carried from elsewhere by a river in the distant past and deposited here, where they became cemented together. Conglomerates like this one (nicknamed "Emerald Lake" by the team) pack a lot of information about places the rover may never visit, with each new rock fragment representing a geologic a story to be told.