The Red Planet is hiding an appealing secret. Scientists have discovered a world-historic discovery on Mars: "significant amounts of water" are hiding inside the Red Planet's Valles Marineris, its version of our grand canyon system, according to a recent press release from the European Space Agency (ESA). And up to 40% of material near the surface of the canyon could be water molecules. The newly discovered volume of water is hiding under the surface of Mars, and was detected by the Trace Gas Orbiter, a mission in its first stage under the guidance of the ESA-Roscosmos project dubbed ExoMars. Signs of water were picked up by the orbiter's Fine Resolution Epithermal Neutron Detector (FREND) instrument, which is designed to survey the Red Planet's landscape and map the presence and concentration of hydrogen hiding in Mars' soil. It works like this: while high-energy cosmic rays plunge into the surface, the soil emits neutrons. And wet soil emits fewer neutrons than dry soil, which enables scientists to analyze and assess the water content of soil, hidden beneath its ancient surface. "FREND revealed an area with an unusually large amount of hydrogen in the colossal Valles Marineris canyon system: assuming the hydrogen we see is bound into water molecules, as much as 40% of the near-surface material in this region appears to be water," said Igor Mitrofanov, the Russian Academy of Science's lead investigator of the Space Research Institute, in the ESA press release. Scientists have already discovered water on Mars, but most earlier discoveries detected the substance crucial to life as we know it near the poles of the Red Planet, subsisting as ice. Only very small pockets of water had shown up at lower latitudes, which was a big downer because future astronauts on Mars will need a lot of water, and there are better prospects for settling the planet at lower latitudes. But now, with what seems like a comparative abundance of water in Valles Marineris, we've taken a major step toward establishing a reliable source of water on the closest alien world.