Dark surface streaks along canyon and crater walls on Mars could be signs of running water presently scouring the surface, according to a new study. The streaks occur in areas thought by some scientists to involve long-running thermal activity under the surface. The salty water seeps to the from below, now and then, because of interactions with hidden, hot, molten rock, the thinking goes. The process is thought to operate somewhat like an ephemeral hot spring on Earth.