Planetary scientists still struggle to clearly define the climate history of Mars billions of years ago. Although there is evidence to suggest the planet's water was flowing freely on its surface, some models instead point to a frigid world where this water was trapped in ice form.

Now, new findings based on Martian minerals, presented at the Goldschmidt Geochemical Conference in Barcelona, suggest the planet might have gone from a warm, wet period full of rainstorms to a colder one at some point between 3 and 4 billion years ago.

“We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely. But we don’t know exactly when these periods were, and how long they lasted. We have never sent unmanned missions to areas of Mars which can show us these earliest rocks, so we need to use Earth-bound science to understand the geochemistry of what may have happened there,” Professor Briony Horgan of Purdue University said in a statement.

Professor Horgan's team looked at how mineral deposits are weathered on Earth in a variety of environments such as Hawaii, Oregon, and Iceland. Using these analogous deposits, they compared the data to that from NASA's CRISM spectrometer and Curiosity.   

“Here on Earth, we find silica deposition in glaciers which are characteristic of melting water,"' said Horgan. "On Mars, we can identify similar silica deposits in younger areas, but we can also see older areas which are similar to deep soils from warm climates on Earth. This leads us to believe that on Mars 3 to 4 billion years ago, we had a general slow trend from warm to cold, with periods of thawing and freezing.”

While geological data continues to point at a wet past for the Red Planet, climate models based on the Sun's heat suggest it must have been a more icy past. Billions of years ago, our star was dimmer and Mars wouldn’t have received enough radiation to maintain liquid water. Still, somehow it may have done so.

“If our findings are correct, then we need to keep working on the Mars climate models, possibly to include some chemical or geological, or other processes which might have warmed the young planet,” said Horgan.

NASA is sending a new rover to Mars next year; hopefully, this will help scientists understand more of Mars' ancient climate.