Photos Suggest Mars Was All Wet, Once

By Andrea Thompson
MSNBC

A lot more Martian rocks were altered by water than scientists originally thought, suggesting that early Mars was a very wet place.

New observations made by NASA’s Mars Reconnaissance Orbiter, currently circling the planet, have revealed evidence that vast regions of the southern highlands of Mars were altered by water in a variety of environments billions of years ago.

Water is a key condition for life as we know it. Though there is no firm evidence that Mars has ever harbored life, knowing that the planet was once wet suggests that it was at least habitable in the past.

The key to the finding is the discovery that rocks called phyllosilicates are widespread on at least the planet’s southern hemisphere. The water present on Mars from about 4.6 billion to 3.8 billion years ago transformed some rocks into these phyllosilicates, which include clays rich in iron, magnesium or aluminum, mica and kaolinite (an ingredient in Kaopectate).

“In a phyllosilicate, the atoms are stacked up into layers, and all of the phyllosilicates have some sort of water or hydroxyl [oxygen and hydrogen group] incorporated into the crystal structure,” said study team member Scott Murchie of Johns Hopkins University.

Previous data from an instrument on Europe’s Mars Express spacecraft — known as OMEGA, or Observatoire pour la Mineralogie, l’Eau, les Glaces et l’Activite — had revealed only a few large outcrops of phyllosilicates, suggesting they were a relative rarity on Mars.

“It sort of gave the false impression that rocks that were altered like this were more restricted than they really are,” Murchie said.

But the new observations, made with MRO’s Compact Reconnaissance Imaging Spectrometer for Mars and detailed in Thursday’s issue of the journal Nature, reveal “thousands and thousands of outcrops that we can now resolve with the higher resolution of the instrument, and they’re scattered all over the planet wherever the older rocks occur,” Murchie told Space.com.

“What that’s suggesting to us is that we’re seeing a pervasive subsurface layer that goes back in time — it’s been altered by water to clays and related minerals, and it’s outcropping all over the place,” Murchie added.

The layer of water-altered rocks sits below younger, volcanic rocks and the ubiquitous windblown Martian dust and sand in many places. But in craters and scarps, including Valles Marineris, across the terrain of the southern hemisphere, the ancient clays and other minerals have been exposed.

“It’s like going to the bottom rock layer in the Grand Canyon,” Murchie said, where ancient layers underlie the whole area, but are only exposed in a few places.

This layering gives scientists a dividing line of about 3.7 to 3.5 billion years ago for a transition in Martian geology:

“Before that the rocks were altered into clays, since then they’re not,” Murchie said.

The variety of clays and other minerals formed also tells scientists that rock was altered by water under a variety of conditions.