NASA’s Mars Reconnaissance Orbiter (MRO) has identified what appear to be ancient hydrothermal deposits in the Eridania region in the southern highlands of Mars. The deposits would represent the remains of a vast inland sea that existed 3.7 billion years ago, according to a study published in the journal Nature Communications.
The Eridania basin of southern Mars is believed to have held a sea about 3.7 billion years ago, with seafloor deposits likely resulting from underwater hydrothermal activity. This graphic shows estimated depths of water in that ancient sea. Image credit: NASA.
The observations by MRO’s Compact Reconnaissance Spectrometer for Mars (CRISM) instrument provided the data for identifying minerals in the Eridania deposits.
“The mix of minerals identified from the CRISM data, including serpentine, talc and carbonate, and the shape and texture of the thick bedrock layers, led to identifying possible seafloor hydrothermal deposits,” said Dr. Paul Niles of NASA’s Johnson Space Center and colleagues.
“The area has lava flows that post-date the disappearance of the sea.”
The researchers interpret the data as evidence that these deposits were formed by heated water from a volcanically active part of the planet’s crust entering the bottom of a large sea.
“This site gives us a compelling story for a deep, long-lived sea and a deep-sea hydrothermal environment,” Dr. Niles said.
“It is evocative of the deep-sea hydrothermal environments on Earth, similar to environments where life might be found on other worlds — life that doesn’t need a nice atmosphere or temperate surface, but just rocks, heat and water.”
The scientists estimate the ancient Eridania sea held about 50,000 cubic miles (210,000 km3) of water.
That is as much as all other Martian lakes combined and about 9 times more than the combined volume of all of North America’s Great Lakes.
This diagram illustrates an interpretation for the origin of some deposits in the Eridania basin of southern Mars as resulting from seafloor hydrothermal activity more than 3 billion years ago. The ground level depicted is an exaggerated topography of a transect about 280 miles (450 km) long. Blue portions of the diagram depict water-depth estimates and the possibility of ice covering the ancient sea. Thick, clay-rich deposits (green) formed through hydrothermal alteration of volcanic materials in deep water, by this model. Notations indicate deep-water reactions of iron and magnesium ions with silicates, sulfides and carbonates. Deep-seated structural discontinuities could have facilitated the ascent of magma from a mantle source. Chloride deposits formed from evaporation of seawater at higher elevations in the basin. Image credit: NASA.
The study adds to the diversity of types of wet environments for which evidence exists on Mars, including rivers, lakes, deltas, seas, hot springs, groundwater, and volcanic eruptions beneath ice.
“Ancient, deep-water hydrothermal deposits in Eridania basin represent a new category of astrobiological target on Mars,” Dr. Niles and co-authors said.
“Eridania seafloor deposits are not only of interest for Mars exploration, they represent a window into early Earth.”
“That is because the earliest evidence of life on Earth comes from seafloor deposits of similar origin and age, but the geological record of those early-Earth environments is poorly preserved.”
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Joseph R. Michalski et al. 2017. Ancient hydrothermal seafloor deposits in Eridania basin on Mars. Nature Communications 8, article number: 15978; doi: 10.1038/ncomms15978
