Martian Water, Past and Present

Mars Express above the thin Martian upper atmosphere successfully achieved orbital insertion on Christmas 2003.
Credit: NASA/JPL

Two new reports from the European Space Agency’s Mars Express satellite were published online this week in the journals Science and Nature, and both provide fresh insight about the presence of water on the Red Planet.

MARSIS, a low-frequency radar sounder on Mars Express, has peered down beneath the soil of Mars, essentially peeling back surface layers without the effort and expense of drilling. MARSIS has conducted two surveys so far — one a few hundred kilometers from the North Pole, and the other in a mid-latitude region.

In the far north, the radar found a water ice deposit under the surface. The ice is nearly pure, with only 2 percent dust mixed in. Future expeditions to drill for that ice will have to battle the extremely strong, rigid crust that caps this region of Mars.

The mid-latitude measurement was made at 35 degrees north latitude, in the Chryse Planitia region. MARSIS revealed that deposition materials flowing from Valles Marineris into this region buried an impact crater. The underground structure is at least 200 kilometers in length, and it may contain water ice.

"The detection of a feature like this suggests that MARSIS can potentially reveal a population of impact craters that have not yet been identified," says Jeffrey Plaut of NASA’s Jet Propulsion Laboratory, Co-Principal Investigator for the MARSIS instrument. "These [craters] would record the early history of Mars in this region which subsequently had a series of resurfacing events."

Scientists hope that MARSIS will discover hidden reservoirs of liquid water. Water is necessary for life as we know it, and, since the planet’s surface is currently too hostile for organisms to survive, underground aquifers would provide a vital refuge for any life on Mars. However, Plaut says the search for liquid water will have to wait until next year.

"We have no convincing evidence yet for subsurface liquid water, but we really have not been in a position to begin the search," Plaut says. "The geometry of the orbit of Mars Express, combined with the time when we initiated the experiment, left us in the position where, for a few weeks beginning in June, [we] had the opportunity to collect the data. Then the orbit drifted into the day side, where the conditions are not optimal for our subsurface sounding. Starting next spring, we will be in a position to begin a detailed search for any hints of liquid water in the subsurface, as the orbit stays in the nighttime and drifts to the warmer mid-latitude areas where it’s more likely that there might be shallow reservoirs of melted H2O."

Liquid water was present on the surface of Mars billions of years ago, according to new information provided by the Mars Express OMEGA instrument. OMEGA, an infrared and visible spectrometer, detected silicates and sulfates that had formed in the presence of water.

The scientists say these hydrated silicates and sulfates formed in different eras during the early history of Mars, and each reflect the environmental conditions of their time.

Phyllosilicates formed during the planet’s first 600 million years, through the aqueous alteration of igneous rocks. These clay-rich phyllosilicate deposits needed to be immersed in water for a long time in order to form.

MARSIS’s long antenna will fly over Mars, bouncing radio waves over a selected area and then receiving and analyzing the "echoes." Any near-surface liquid water should send a strong signal.
Credit: NASA/JPL

The sulfates, however, which developed as salt deposits in acidic water, did not require a long soak for their formation.

The two different kinds of hydrated minerals provide clues to the early evolution of the martian climate. The phyllosilicates formed in the warm and wet climate of young Mars, when open bodies of water were more plentiful. Then as Mars began to lose its atmosphere and the surface water evaporated into space, the rapidly drying ponds became more acidic and formed the hydrated sulfates.

"Between the silicate era and the sulfate era, Mars underwent a huge global change, out of which the atmosphere, if ever it was present, was lost," says Jean-Pierre Bibring, OMEGA Principal Investigator.

Mars may have been habitable for life during the era when the phyllosilicate clays formed. The clays were detected mainly in the Arabia Terra, Terra Meridiani, Syrtis Major, Nili Fossae and Mawrth Vallis regions, and these could be prime spots to search for evidence of past martian life.

"If life began on Mars, it could be preserved in these clay minerals," says Bibring. "[Mapping] the clay shows where we should go in the future, if we want to look for the astrobiological record of Mars."