Mars Has Frozen Ice Today, But It Is Thought To Have Once Been Liquid

The presence of water on a planet is regarded to be one of the primary requirements for life. Although liquid water is ideal for life as we know it, the mere fact that water exists at all suggests that life may exist on a planet (or has been present in the past).

In the case of Mars, scientists are certain that the planet's poles contain significant amounts of ice. Since the atmosphere of the planet is so thin, there is little to no chance that liquid water could exist there, as far as we know.

Outside of Mars' polar regions, whatever water that may exist is most likely also frozen. However, NASA spacecraft like the Curiosity Rover continue to scour the planet for probable sites where life might exist. Even if there isn't life on Mars, the vast amounts of frozen water will be a fantastic resource for any upcoming human settlements and missions to the planet.

But might this solid ice have ever been liquid? The scientific community is divided on this issue, and debates have been going on for more than a century. Several spacecraft have observed indicators of what appear to be ancient river channels, fluvial plains, and other hydrological features that may be proof of liquid water in the past, after early misinterpretations of formations that mimic deliberately created water canals.