Recent measurements by NASA’s Curiosity rover indicate that a huge lake once filled much of Gale Crater for millions and millions of years and thus possessed the right environmental conditions for a long enough time span to significantly increase the chances that simple microbial life forms could possibly have formed and persisted on Mars billions of years ago.
Scientists announced the discovery of a vast ancient lake at Gale and that Mount Sharp was subsequently created inside the crater by the deposition of sediments into the large lake bed over tens of millions of years, during a NASA media briefing today, Dec. 8.
“Mars changed over time,” said Ashwin Vasavada, Curiosity deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., at the briefing.
“Rivers and lakes were present over millions of years.”
Curiosity safely touched down inside Gale Crater in August 2012.
Since then, the six-wheeled rover has been on an epic trek traversing more than 5 miles (8 kilometers) across the crater floor to conduct detailed observations at a number of scientifically interesting sites along the way, including making a multi-month detour in early 2013 to a region called “Yellowknife Bay.”
She conducted five rock drilling operations since landing to ingest pulverized samples for chemical analysis to elucidate Mars’ history of potential habitability, and discovered a habitable zone at Yellowknife Bay.
Gale Crater was selected several years ago by the science team as Curiosity’s landing site precisely because the team suspected the presence of an ancient lake based on spectroscopic observations captured from Mars orbit by NASA and ESA robotic spacecraft orbiting the Red Planet.
“We selected Gale because of Mount Sharp and its layered minerals with a record of early Mars history,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington.
“But how did the mountain form in the middle of the crater?”
The origin of Mount Sharp has puzzled researchers and generated a lot of debate in the scientific community.
Gale Crater itself was originally formed by excavation from a meteorite impact billions of years ago. There may have been a small central peak formed as a rebound from the impact that could have appeared as an island in the ancient lake.
Today, Gale Crater looks vastly different compared to ancient Mars. It is overwhelmed by Mount Sharp which dominates the center of the 96 mile wide (154 kilometers) crater and towers 3.4 miles (5.5 kilometers) into the Martian sky.
Gale Crater lake existed long before Mount Sharp ever formed, during a period billions of years ago when the Red Planet was far warmer and wetter than it is now.
But for reasons we are still trying to decipher and comprehend, Mars underwent radical climactic change between 3 and 4 billion years ago and was transformed from an ancient wet world—potentially hospitable to life—to a cold, dry desiccated world—rather inhospitable to life—that exists today.
Unlocking the mysteries, mechanisms, and time periods of Mars’ climate change, loss of a thick atmosphere, ability to sustain liquid surface water and searching for organic compounds, and for evidence of past or present habitable zones favorable to life are the questions driving NASA’s Mars Exploration program.
“If our hypothesis for Mount Sharp holds up, it challenges the notion that warm and wet conditions were transient, local, or only underground on Mars,” said Ashwin Vasavada, Curiosity deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
“A more radical explanation is that Mars’ ancient, thicker atmosphere raised temperatures above freezing globally, but so far we don’t know how the atmosphere did that.”
The lower flanks of Mount Sharp are filled with hundreds of exposures of sedimentary rock layers.
The rock layers alternating between lake, river, and wind deposits bear witness to the repeated filling and evaporation of a Martian lake much larger and longer-lasting than any previously examined close-up, according to a statement from the science team.
“We are making headway in solving the mystery of Mount Sharp,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. “Where there’s now a mountain, there may have once been a series of lakes.”
“We are fitting together a jigsaw puzzle,” said Curiosity science team member Sanjeev Gupta of Imperial College in London.
Gale Crater lake was gradually filled in by sediments deposited over tens of millions of years.
“The lake was only a few meters deep,” Gupta told AmericaSpace.
The sediments accumulated from rivers, lakes, deltas, and streams as water carrying sand and silt flowed in from the mountainous crater rim, much like river mouths on Earth, and deposited the sediments to form the lower layers of Mount Sharp. These are believed to be the oldest layers and hold the minerals most conducive to the formation of life.
“We found sedimentary rocks suggestive of small, ancient deltas stacked on top of one another,” said Gupta. “Curiosity crossed a boundary from an environment dominated by rivers to an environment dominated by lakes.”
Over time the rim was gradually eroded by weathering and melting snow as the deposition cycle was repeated over and over again. The crater rim was much higher three billion years ago, according to the team.
“The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works,” Grotzinger said.
“As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year.”
Curiosity arrived at the foothills of Mount Sharp in September at a spot dubbed the Pahrump Hills. This area comprises the lowest sedimentary layers of Mount Sharp at a section of rock 500 feet (150 meters) high, dubbed the Murray formation. The one-ton robot is analyzing a drill sample dubbed “Confidence Hills.”
The rover recently completed a walkabout of the Pahrump Hills to determine the best location for the next drill campaign.
So far Curiosity’s odometer totals over 5.5 miles (9.0 kilometers) since landing inside Gale Crater on Mars in August 2012. She has taken some 203,000 images during over 820 Sols of exploration.
Stay tuned here for continuing updates.
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