Curiosity rover finds evidence of stratified ancient Martian lake
A recent comprehensive study of data from the first three-and-a-half years of NASA’s Curiosity mission indicates that a long-lasting ancient lake on Mars had stable environmental conditions that differed significantly from one part of the lake to another. Different conditions that were suitable for different types of microbes existed simultaneously in the lake.
Earlier research revealed evidence of a lake more than three billion years ago in Mars’ Gale Crater. The new study defines the chemical conditions that had existed in the lake and uses Curiosity’s science instruments to determine that the lake was stratified. Stratified bodies of water show marked chemical or physical differences between deep and shallow water. In the lake at Gale’s Crater, the shallow water was richer in oxidants than the deeper water was.
“These were very different, co-existing environments in the same lake,” said Joel Hurowitz of Stony Brook University, Stony Brook, New York, lead author of a report of the findings in the June 2 edition of the journal Science. “This type of oxidant stratification is a common feature of lakes on Earth, and now we’ve found it on Mars. The diversity of environments in this Martian lake would have provided multiple opportunities for different types of microbes to survive, including those that thrive in oxidant-rich conditions, those that thrive in oxidant-poor conditions, and those that inhabit the interface between those settings.”
When Curiosity first landed inside Gale Crater in 2012, the rover’s primary goal was to determine whether environmental conditions on Mars had ever been favorable for microbial life. During the mission’s first year on Mars, Curiosity found evidence of ancient freshwater river and lake environments at “Yellowknife Bay” – a site on the crater floor. Since then, Curiosity has made its way to Mount Sharp – a layered mountain (officially known as Aeolis Mons) inside the crater. The rover has studied progressively younger rock layers as it drives to higher elevations on lower Mount Sharp.
The team was, at first, puzzled by differences in the physical, chemical, and mineral characteristics of several sites on lower Mount Sharp. For instance, some rocks showed thicker layering with a large proportion of an iron mineral called hematite, while other rocks showed very fine layers and more of an iron mineral called magnetite. Scientists pondered whether these differences were the result of environmental conditions fluctuating over time or differing from place to place.
“We could tell something was going on,” Hurowitz said. “What was causing iron minerals to be one flavor in one part of the lake and another flavor in another part of the lake? We had an ‘Aha!’ moment when we realized that the mineral information and the bedding-thickness information mapped perfectly onto each other in a way you would expect from a stratified lake with a chemical boundary between shallow water and deeper water.”
The report written by Hurowitz and 22 co-authors also documents fluctuations in the ancient climate of Mars. One such change occurred between the time rocks on the crater floor were deposited and the time when the rocks that make up the base of Mount Sharp were deposited. These younger rocks are exposed at “Pahrump Hills” and other sites.
“These results give us unprecedented detail in answering questions about ancient environmental conditions on Mars,” said Curiosity Project Scientist Ashwin Vasavada of NASA’s Jet Propulsion Laboratory, Pasadena, California. “I’m struck by how these fascinating conclusions on habitability and climate took everything the mission had to offer: a set of sophisticated science instruments, multiple years and miles of exploration, a landing site that retained a record of the ancient environment, and a lot of hard work by the mission team.”
Jim Sharkey is a lab assistant, writer and general science enthusiast who grew up in Enid, Oklahoma, the hometown of Skylab and Shuttle astronaut Owen K. Garriott. As a young Star Trek fan he participated in the letter-writing campaign which resulted in the space shuttle prototype being named Enterprise. While his academic studies have ranged from psychology and archaeology to biology, he has never lost his passion for space exploration. Jim began blogging about science, science fiction and futurism in 2004. Jim resides in the San Francisco Bay area and has attended NASA Socials for the Mars Science Laboratory Curiosity rover landing and the NASA LADEE lunar orbiter launch.