There's still debate about whether water exists or ever existed on Mars.

This is an important question, because if water does exist, it means that Mars might harbor life.

I never imagined so much water existed in the universe.

By increasing the pressure, the water can exist as a liquid even when the temperature is above 212 degrees.

And up there, if water exists, and air, then so does life.

Free water exists in the equatorial regions all year round.

But that water exists in only a few places.

For an estimated explanation of where Earth's water exists, look at the chart below.

If the atmospheric composition had been the same as today, liquid water should not have existed on Earth.

The rover is expected to spend at least 90 days looking for evidence that water once existed on the planet.