Carbon Rocks Deep Underground Could Hold the Evidence of Mars' Watery Past.

What happened

In addition to the scarcity of carbonate rocks on Mars' surface, scientists have also puzzled over why the carbonates that have been found fall into two distinct groups: calcium- and iron-rich and magnesium-rich rocks. A new geochemical modeling study led by researchers at JAXA and the University of Tokyo addresses Mars' "missing" stores of carbonate rocks.

The paper that describes their findings recently appeared in the journal JGR Planets . Though carbonates are present on Mars, they're not abundant.

If Mars were wet for a long time, they should be abundant. Previous research on water-rock interactions on Mars billions of years ago has assumed that water interacted with the planet's most common rock types, which are composed of mafic, iron-, and magnesium-rich minerals.

Feldspar-rich rocks, however, have been increasingly detected on the planet's surface by orbiters and rover missions. These rock-forming minerals are also the most abundant group on Earth, accounting for 60% of the Earth's crust. The simulations were based on the PHREEQC Version 3 geochemical code, which performs a wide variety of aqueous geochemical calculations.