Why Is There Water on Mars?

Almost all water on Mars today exists as ice, though it also exists in small quantities as vapor in the atmosphere. What was thought to be low-volume liquid brines in shallow Martian soil, also called recurrent slope lineae, may be grains of flowing sand and dust slipping downhill to make dark streaks.

How did Mars get water?

Once a warm, wet world, Mars lost its magnetic field more than 4 billion years ago when its outer core cooled, shutting off the dynamo that kept the field in place. That exposed the planet to the solar wind, which clawed away at the atmosphere; and that in turn allowed the planet's water to sputter off into space.

Where did water on Mars go?

Mars once had water flowing over the surface, but it disappeared billions of years ago. A new study suggests that in addition to being lost to space, much of the water could have been trapped in minerals in the planet's crust.