Was Mars once green?

For the most part, scientists are in agreement that Mars once had much more surface water than it does today. But the debate still rages as to whether the red planet had a warm enough climate for liquid water. Now, a new study has provided more compelling evidence in favor of a wet Mars. Moreover, Mars may have even had rainstorms, as Newsweek reports.

Briony Horgan of Purdue University recently presented her team’s findings at the Goldschmidt Geochemistry Conference in Barcelona. “We know there were periods when the surface of Mars was frozen; we know there were periods when water flowed freely,” Horgan said in a statement. “But we don’t know exactly when these periods were, and how long they lasted.”

Smoking Gun

Horgan’s team uncovered clues about Mars’ ancient climate by comparing data sets of Martian mineral deposits collected by NASA’s rovers and spacecraft with similar patterns on regions of Earth that are considered Mars analogs. These areas include the Oregon Cascades, Hawaii, and Iceland.

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The smoking gun was the discovery of silica deposits on Mars. These deposits proved similar to silica deposits found in Earth glaciers. Earth glaciers are constantly in flux, melting and refreezing. This led planetary scientists to believe that Mars was once warm enough for ice to melt.

Furthermore, the team observed older areas of Mars with soil that shared characteristics with deep soils from a time when Earth was much warmer. “This leads us to believe that on Mars three to four billion years ago, we had a general slow trend from warm to cold, with periods of thawing and freezing,” Horgan said.

Have You Ever Seen the Rain?

The evidence that Mars did indeed have liquid water on its surface is piling up. The most obvious is that the Martian landscape is full of ancient river beds and basins where oceans may have even existed. A recent study also provided compelling evidence that a meteorite impact in an ancient Martian ocean caused a mega-tsunami on the red planet. But as the study also posited, Mars’ water could have come from subterranean aquifers.

So what about those rainstorms? Just because Mars had flowing water, doesn’t necessarily mean it had a hydrologic cycle like Earth. “Rainstorms on Mars” might be a great headline, but is there evidence? Horgan’s team says yes. Geochemical processes observed on Mars seem to be similar to those on Earth only known to form “under persistent rain-dominated climates,” as the team states in their abstract.

The evidence for liquid water on ancient Mars and possibly even rainstorms is compelling. Furthermore, with the possibility of flowing water also comes the possibility of life. But science always needs definitive proof. Horgan is optimistic that the upcoming Mars 2020 rover will provide that proof. “We hope that the Mars 2020 mission will be able to look more closely at these minerals, and begin to answer exactly what conditions existed when Mars was still young.”

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