Liquid water cannot really exist for very long on Mars because of the low pressure and the low temperature. However, scientists believe that liquid water can/does exist on some moons of Jupiter even though it is much farther from the sun. How can that be you say…well, because of the many different moons in the Jupiter system the orbits are elliptical which means that the moons are often closer to Jupiter at times. This means that there are tidal forces at work that cause ‘tidal heating’ which is the stretching of the moon and the rocks moving and creating a lot of friction. This causes the heat which is enough to allow liquid water on the moon.

(The Great Courses – Life in Our Universe)