During a news conference this week, NASA announced that, using spectral analysis, the Mars Reconnaissance Orbiter detected what scientists believe to be definitive signs of liquid water on Mars.

No, the orbiter didn’t detect water flowing through mythical “canals” once thought to be crisscrossing the red planet’s surface. The announcement sounds borderline unsexy when laid out scientifically.

NASA now believes that what it calls “recurring slope lineae,” the dark streaks that run downhill on the sides of craters and other vertical topography during the Martian summer, are evidence that liquid water exists just beneath the planet’s surface.

This is a big deal, because the presence of liquid water is arguably the most necessary element for the evolution of life as we know it. The water on Mars is believed to be briny and far saltier than any on Earth. It isn’t drinkable and would be toxic to bacterial life from Earth, but it may have harbored Martian single-cell life at one time. It may currently be the home of life that has adapted to its harsh chemistry.

NASA’s scientists are confident that what they’re describing as seepage on the surface is evidence of subsurface reservoirs and rivers. Theories are already starting to circulate about what Mars may have been like 3.5 billion years ago and when it was covered with oceans.

The presence of water beneath the surface could also mean we’re on the verge of discovering life on another planet.

This tantalizing possibility is all the more reason for NASA to proceed with more robotic missions to Mars in preparation for manned missions in the 2020s and 2030s. This is the most exciting news about Mars in a very long time.