Layers in the lower portion of two neighboring buttes within the Noctis Labyrinthus formation on Mars are visible in this image from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter. The discovery of martian clay rich in minerals formed by water suggests the region may have hosted life relatively recently.
Credit: NASA/JPL-Caltech/University of Arizona
The Noctis Labyrinthus, which formed when the Martian crust stretched and fractured. As faults opened, they released subsurface ice and water, causing the ground to collapse. This westward view combines images taken during the period from April 2003 to September 2005 by the Thermal Emission Imaging System instrument on NASA's Mars Odyssey orbiter.
Credit: NASA/JPL-Caltech/ASU
SYDNEY: The discovery of Martian clays rich in minerals formed by water activity suggest the planet could have supported life relatively recently in its history.
Identified from data collected by NASA's Mars Reconnaissance Orbiter (MRO), the minerals were found inside two small depressions in a region of the planet known as Noctis Labyrinthus, or the 'labyrinth of the night'.
The findings, published earlier this month in the journal Geology, suggest the region may have previously been habitable when drier conditions existed on the planet's surface.
"We discovered locations at Noctis Labyrinthus that show many kinds of minerals that formed by water activity," said Catherine Weitz, lead author and senior scientist at the Planetary Science Institute in Arizona.
"The clays we found, called iron/magnesium (Fe/Mg)-smectites, are much younger at Noctis Labyrinthus relative to those found in the ancient rocks on Mars, which indicates a different water environment in these depressions relative to what was happening elsewhere on Mars."
Mapping hydrated minerals
Smectites are a specific type of clay mineral that expand and contract when immersed in water. They are common on Earth where they form by chemical reactions between circulating water and primary silicate rocks.
Weitz and her co-authors studied approximately 300 meters of vertically exposed layered rocks within two 30 to 40-kilometre-wide depressions, called troughs, near the western end of the Valles Marineris canyon system.
The team used high-resolution images and hyperspectral data from instruments aboard the MRO spacecraft. They combined this with digital terrain models to determine elevations and view geometric relationships between units.
The team was then able to map hydrated minerals and understand how the water chemistry had varied with time within each trough, said Weitz.
Retracing water activity and volcanism
Each trough probably experienced multiple episodes where water partially filled in low-lying regions and deposited minerals.
As each trough continued to enlarge and experience collapse over time, older minerals became buried and separated, followed by deposition of younger minerals, then finally erosion to re-expose buried units.
Volcanism from the Tharsis volcanoes to the west may have created subsurface water that was subsequently transported through the ground and into the troughs.
Localised volcanism that produced ash and gases, hydrothermal activity, and melting snow or ice within the troughs could have also produced some of the minerals.
The observed minerals indicate water varied in pH levels over time, in one trough from acidic to neutral, and in the other trough from neutral to acidic and back to neutral.
Potential oasis for life
"These types of minerals had already been discovered in some of the older terranes on Mars when the climate there may have been warmer and wetter," explained geologist Marc Norman from the Australian National University, who was not involved in the study.
"But life may not have had a chance to get started or at least would have been very simple and perhaps difficult to recognise or distinguish from abiogenic chemicals."
The significance of this discovery, said Norman, "is that they found these hydrated alteration products in a much younger geological terrane of Mars, which looks like it has an age of perhaps only 2 billion years old".
This is less than half the age of the solar system - both Earth and Mars are about 4.5 billion years old. At the same time life on Earth was robust and complex, making it easier to identify as uniquely biological, commented Norman.
"This terrane may have provided an oasis for life on Mars to survive and evolve, and would certainly be an interesting place to explore further with landers and possibly sample return missions to bring real material back to labs on Earth for detailed study," he added.
However, such a mission may prove too risky given the landscape. "These troughs would be fantastic places to send a rover, but unfortunately the rugged terrain makes it unsafe both for landing and for driving," said Weitz.
