The Mars of popular imagination is primarily dry, dusty, and secretly inhabited by benevolent aliens who spawned mankind—but NASA reported Monday that they have discovered signs of salty, liquid water on the Red Planet's surface.
Scientists have known for years that Mars has water frozen in the ice caps at its poles, and the planet is covered in clues pointing to the fact that it once housed an ocean—but this is the first time anyone has found current evidence of sweet, wet, liquid-y, life-giving water on the planet.
The signs of water don't point toward gushing geysers or previously-undiscovered alien lakes, but NASA is convinced that long, dark stains of waterlogged salt streaking down Martian mountains are the result of brackish water trickling down the planet's surface in the summer months.
Scientists aren't sure how much water there is or where it is originating (the water may be coming from Mars's atmosphere, or it could be seeping to the surface from melting patches of underground ice) but there is water, by God, and water means life—both for potential alien species and for humans if we want to colonize.
NASA hasn't actually seen water yet—just these streaks that are the result of water that has since dried up. But we know it exists, so there will at least be a little bit of water for an intrepid astronaut to salvage once we accidentally leave them behind during the inevitable Mars mission.