NASA Curiosity First Mars Age Measurement and Human Exploration Help

8/10/2019 NASA Curiosity First Mars Age Measurement and Human Exploration Help

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12.09.2013Source: Jet Propulsion Laboratory

NASA Curiosity: First Mars Age Measurement and Human ExplorationHelp

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Curiosity research papers associated with this news release:http://mars.jpl.nasa.gov/msl/mission/science/researchpapers/

Erosion by Scarp Retreat in Gale CraterThis mosaic of images from the Mast Camera (Mastcam) instrument on NASA's Curiosity Mars rover shows a series ofsedimentary deposits in the Glenelg area of Gale Crater, from a perspective in Yellowknife Bay looking toward west-northwest.

NASA's Curiosity rover is providing vital insight about Mars' past and current environments that willaid plans for future robotic and human missions.

In a little more than a year on the Red Planet, the mobile Mars Science Laboratory has determinedthe age of a Martian rock, found evidence the planet could have sustained microbial life, taken thefirst readings of radiation on the surface, and shown how natural erosion could reveal the buildingblocks of life. Curiosity team members presented these results and more from Curiosity in six paperspublishedonlinetoday by Science Express and in talks at the Fall Meeting of the AmericanGeophysical Union in San Francisco.Watch televised news briefing.

The Age of 'Cumberland'

The second rock Curiosity drilled for a sample on Mars, which scientists nicknamed "Cumberland," isthe first ever to be dated from an analysis of its mineral ingredients while it sits on another planet. Areport by Kenneth Farley of the California Institute of Technology in Pasadena, and co-authors,estimates the age of Cumberland at 3.86 billion to 4.56 billion years old. This is in the range ofearlier estimates for rocks in Gale Crater, where Curiosity is working.
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"The age is not surprising, but what is surprising is that this method worked using measurementsperformed on Mars," said Farley. "When you're confirming a new methodology, you don't want thefirst result to be something unexpected. Our understanding of the antiquity of the Martian surfaceseems to be right."

View of Yellowknife Bay Formation, with Drilling SitesThis mosaic of images from Curiosity's Mast Camera (Mastcam) shows geological members of the Yellowknife Bayformation, and the sites where Curiosity drilled into the lowest-lying member, called Sheepbed, at targets "John Klein" and"Cumberland."

The analysis of Cumberland from a sample drilled by Curiosity was a fundamental andunprecedented measurement considered unlikely when the rover landed in 2012. Farley and his co-authors adapted a 60-year-old radiometric method for dating Earth rocks that measures the decay ofan isotope of potassium as it slowly changes into argon, an inert gas. Argon escapes when a rock ismelted. This dating method measures the amount of argon that accumulates when the rock hardensagain.

Before they could measure rocks directly on Mars, scientists estimated their ages by counting andcomparing the numbers of impact craters on various areas of the planet. The crater densities arecorrelated with ages based on comparisons with crater densities on the moon, which were tied toabsolute dates after the Apollo lunar missions returned rocks to Earth.

Farley and co-authors also assessed how long Cumberland has been within about an arm's reach ofthe Martian surface, where cosmic rays that hit atoms in the rock produce gas buildups that Curiosity

can measure.

Analyses of three different gases yielded exposure ages in the range of 60 million to 100 millionyears. This suggests shielding layers above the rock were stripped away relatively recently.Combined with clues of wind erosion Curiosity observed, the exposure-age discovery points to apattern of windblown sand chewing away at relatively thick layers of rock. The eroding layer forms aretreating vertical face, or scarp.

"The exposure rate is surprisingly fast," Farley said. "The place where you'll find the rocks with theyoungest exposure age will be right next to the downwind scarps."

From Rocks to Building Blocks?

Finding rocks with the youngest exposure age is important in the mission's investigations of whetherorganic chemicals are preserved from ancient environments. Organic chemicals are building blocksfor life, although they also can be produced without any biology.

"We're making progress on the path to determining whether there are Martian organics in there,"Doug Ming, of NASA's Johnson Space Center, Houston, said of the Cumberland rock sample. "Wedetect organics but can't rule out that they might be brought along from Earth." Curiosity detectedhigher amounts in Cumberland than it did in in either test runs with Martian soil samples or analysis
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of empty sample cups. Increasing the amount of rock powder in the test cup increased the amount oforganic content detected.

Favorable for Life

Possible Extent of Ancient Lake in Gale Crater, MarsThis illustration depicts a concept for the possible extent of an ancient lake inside Gale Crater.

Ming is the lead author of a new report about a site called "Yellowknife Bay." The team reported 10months ago that the first rock Curiosity drilled there, nicknamed "John Klein," yielded evidence thatmet the mission's goal of identifying a Martian environment favorable for microbial life long ago.Yellowknife Bay's clay-rich lakebed habitat offers the key chemical elements for life, plus water nottoo acidic or salty, and an energy source. The energy source is a type used by many rock-eatingmicrobes on Earth: a mix of sulfur- and iron-containing minerals that are ready acceptors ofelectrons, and others that are ready electron donors, like the two poles of a battery.

Not only has Curiosity accomplished its primary goal of finding evidence for an ancient environmentthat could have supported life, but it also has provided evidence habitable conditions existed morerecently than expected and likely persisted for millions of years.

Additional new results from Curiosity are providing the first readings of radiation hazards at Mars'surface, which will aid planning of human missions to Mars. Other findings will guide the search forevidence of life on Mars by improving insight about how erosion may expose buried clues ofmolecular building blocks of life.

New estimates of when habitable conditions existed at Yellowknife Bay and how long they persistedcome from details of rocks' composition and layering. It is thought that Mars had enough fresh waterto generate clay minerals -- and possibly support life -- more than 4 billion years ago, but that theplanet underwent drying that left any remaining liquid water acidic and briny. A key question waswhether the clay minerals at Yellowknife Bay formed earlier, upstream on the rim of Gale Crater

where the bits of rock originated, or later, downstream where the rock particles were carried by waterand deposited.

Scott McLennan of Stony Brook University in Stony Brook, N.Y., and co-authors found that chemicalelements in the rocks indicate the particles were carried from their upstream source area toYellowknife Bay and that most chemical weathering occurred after they were deposited. The loss ofelements that leach easily, such as calcium and sodium, would be noticeable if the weathering thatturns some volcanic minerals into clay minerals had happened upstream. Scientists did not noticesuch leaching.
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David Vaniman of the Planetary Science Institute in Tucson, Ariz., and co-authors found supportingevidence in a separate mineral analysis of sedimentary rocks at Yellowknife Bay. They noticed alack of olivine and an abundance of magnetite, which suggests the rocks turned to clay after theywashed downstream. The presence of smectite tells about conditions where the clay formed.

"Smectite is the typical clay mineral in lake deposits," Vaniman said. "It is commonly called a

swelling clay -- the kind that sticks to your boot when you step in it. You find biologically richenvironments where you find smectites on Earth."

John Grotzinger of Caltech and co-authors examined physical characteristics of rock layers in andnear Yellowknife Bay and concluded the habitable environment there existed at a time "relativelyyoung by Martian standards." It was a part of Martian history called the Hesperian Era, when parts ofthe planet were already becoming drier and more acidic, less than 4 billion years ago and roughlythe same time as the oldest evidence for life on Earth.

"This habitable environment existed later than many people thought there would be one," Grotzingersaid. "This has global implications. It's from a time when there were deltas, alluvial fans and othersigns of surface water at many places on Mars, but those were considered too young, or too short-

lived, to have formed clay minerals. The thinking was, if they had clay minerals, those must havewashed in from older deposits. Now, we know the clay minerals could be produced later, and thatgives us many locations that may have had habitable environments, too."

Research suggests habitable conditions in the Yellowknife Bay area may have persisted for millionsto tens of millions of years. During that time rivers and lakes probably appeared and disappeared.Even when the surface was dry, the subsurface likely was wet, as indicated by mineral veinsdeposited by underground water into fractures in the rock. The thickness of observed and inferredtiers of rock layers provides the basis for estimating long duration, and the discovery of a mineralenergy source for underground microbes favors habitability throughout.

Implications for Human Explorers

Radiation Exposure Comparisons with Mars Trip CalculationMeasurements with the MSL Radiation Assessment Detector (RAD) on NASA's Curiosity Mars rover during the flight to Marsand now on the surface of Mars enable an estimate of the radiation astronauts would be exposed to on an expedition toMars.
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Today's reports include the first measurements of the natural radiation environment on the surface ofMars. Cosmic rays from outside our solar system and energetic particles from the sun bombardedthe surface at Gale Crater with an average of 0.67 millisieverts per day from August 2012 to June2013, according to a report by Don Hassler of Southwest Research Institute in Boulder, Colo., and

co-authors. For comparison, radiation exposure from a typical chest X-ray is about 0.02 millisievert.That 10-month measurement period did not include any major solar storms affecting Mars, and morethan 95 percent of the total came from cosmic rays.

Results from the surface-radiation monitoring provide an additional piece of the puzzle for projectingthe total round-trip radiation dose for a future human mission to Mars. Added to dose rates Curiositymeasured during its flight to Mars, the Mars surface results project a total round-trip dose rate for afuture human mission at the same period in the solar cycle to be on the order of 1,000 millisieverts.

Long-term population studies have shown exposure to radiation increases a person's lifetime cancerrisk. Exposure to a dose of 1,000 millisieverts is associated with a 5 percent increase in risk fordeveloping fatal cancer. NASA's current career limit for increased risk for its astronauts currently

operating in low-Earth orbit is 3 percent. The agency is working with the Institute of Medicine of theNational Academies to address the ethics, principles and guidelines for health standards for longduration and exploration spaceflight missions.

The radiation detected by Curiosity is consistent with earlier predictions. The new data will helpNASA scientists and engineers create better models to anticipate the radiation environment humanexplorers will face, as the agency develops new technologies to protect astronauts in deep space.

"Our measurements provide crucial information for human missions to Mars," Hassler said. "We'recontinuing to monitor the radiation environment and seeing the effects of major solar storms on thesurface at different times in the solar cycle, will give additional important data. Our measurementsalso tie into Curiosity's investigations about habitability. The radiation sources that are concerns forhuman health also affect microbial survival as well as preservation of organic chemicals."

If any organic chemicals that are potential signs of life did exist within rocks at about 2 inches (5centimeters), the depth of Curiosity's drill, Hassler estimated they would be depleted up to 1,000-foldin about 650 million years by radiation at the exposure rate measured in Curiosity's first 10 months.However, the Cumberland rock that Curiosity sampled with its drill at Yellowknife Bay had beenexposed to cosmic rays' effects for only about 60 million to 100 million years, by Farley's estimate.Researchers calculate that, with such a young exposure age, enough organic material could still bepresent in Cumberland to be detectable. Even if Mars has never supported life, the planet receivesorganic molecules delivered by meteorites, which should leave a detectable trace.

NASA's Jet Propulsion Laboratory built Curiosity and manages the mission for NASA's ScienceMission Directorate, Washington.

For more information about the mission, visit:http://www.nasa.gov/mslandhttp://mars.jpl.nasa.gov/msl
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NASA Curiosity First Mars Age Measurement and Human Exploration Help