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Science

SwRI scientists publish first radiation measurements from the surface of Mars
In the first 300 days of the Mars Science Laboratory's surface mission, the Curiosity rover cruised around the planet's Gale Crater, collecting soil samples and investigating rock structures while the onboard Radiation Assessment Detector made detailed measurements of the radiation environment on the surface of Mars.
NASA

Contact: Deb Schmid
dschmid@swri.org
210-522-2254
Southwest Research Institute

 

 

 

SwRI scientists publish first radiation measurements from the surface of Mars

Space Science & Engineering

For immediate release

Boulder, Colo. — Dec. 9, 2013 — In the first 300 days of the Mars Science Laboratory surface mission, the Curiosity rover cruised around the planet's Gale Crater, collecting soil samples and investigating rock structures while the onboard Radiation Assessment Detector made detailed measurements of the radiation environment on the surface of Mars.

SwRI scientists published radiation surface dose rates from the first 300 days on Mars in Science online Dec. 9. Curiosity's Radiation Assessment Detector observed a spike in the radiation dose associated with one hard solar energetic particle event and three dips in radiation associated with soft interplanetary coronal mass ejections, which provided magnetic shielding against galactic cosmic rays. Occasional brief gaps are typically when RAD was powered off to minimize interference with other activities.

"Our measurements provide crucial information for human missions to Mars," said Dr. Don Hassler, a Southwest Research Institute program director and RAD principal investigator. Hassler is the lead author of "Mars' Surface Radiation Environment Measured with the Mars Science Laboratory's Curiosity Rover," scheduled for publication in the journal Science online on December 9, 2013. "We're continuing to monitor the radiation environment, and seeing the effects of major solar storms on the surface and at different times in the solar cycle will give additional important data. Our measurements also tie into Curiosity's investigations about habitability. The radiation sources that are of concern for human health also affect microbial survival as well as the preservation of organic chemicals."

Two forms of radiation pose potential health risks to astronauts: a chronic low dose of galactic cosmic rays (GCRs) and the possibility of short-term exposures to the solar energetic particles (SEPs) associated with solar flares and coronal mass ejections. The radiation on Mars is much harsher than on Earth for two reasons: Mars lacks a global magnetic field and the Martian atmosphere is much thinner than Earth's, providing little shielding to the surface.

This environmental factor poses a challenge for future human exploration of Mars and is also important in understanding both geological and potential biological evolution on Mars. Both GCRs and SEPs interact with the atmosphere and, if energetic enough, penetrate into the Martian soil, or regolith, where they produce secondary particles that contribute to the complex radiation environment on the Martian surface, which is unlike anything on Earth.

"The RAD surface radiation data show an average GCR dose equivalent rate of 0.67 millisieverts per day from August 2012 to June 2013 on the Martian surface," said Hassler. Radiation dose is measured in units of sievert (Sv) or millisievert (1/1000 Sv). "In comparison, RAD data show an average GCR dose equivalent rate of 1.8 millisieverts per day on the journey to Mars, when RAD measured the radiation inside the spaceship."

Using the data collected by SwRI's Radiation Assessment Detector onboard the Curiosity rover, this chart compares the radiation dose equivalent for a 500-day stay on Mars to the dose associated with a 180-day journey to Mars, a six-month stay on the International Space Station and several Earth-based sources of radiation.

According to RAD data, most mission radiation exposure will be during outbound and return travel, when the astronauts will be exposed to the radiation environment in interplanetary space, shielded only by the spacecraft itself. The total during just the transit phases of a Mars mission would be approximately 0.66 Sv for a round trip with current propulsion systems and during similar solar activity. A 500-day mission on the surface would bring the total exposure to around 1 Sv.

Long-term population studies have shown that exposure to radiation increases a person's lifetime cancer risk; exposure to a dose of 1 Sv is associated with a five percent increase in fatal cancer risk. Although NASA has generally established a three percent increased risk of fatal cancer as an acceptable career limit for astronauts in low earth orbit, it does not currently have a limit for deep space missions, and is working with the National Academies Institute of Medicine to determine appropriate limits for deep space missions, such as a mission to Mars in the 2030s.

SwRI, together with Christian Albrechts University in Kiel, Germany, built RAD with funding from the NASA Human Exploration and Operations Mission Directorate and Germany's national aerospace research center, Deutsches Zentrum für Luft- und Raumfahrt.

NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology, Pasadena, Calif., manages the Mars Science Laboratory Project. The NASA Science Mission Directorate, at NASA Headquarters in Washington, manages the Mars Exploration Program.

"Mars' Surface Radiation Environment Measured with the Mars Science Laboratory's Curiosity Rover," published in Science online December 9, was written by Hassler, Cary Zeitlin of SwRI, Robert F. Wimmer-Schweingruber of Christian Albrechts University, Bent Ehresmann of SwRI, Scot Rafkin of SwRI, Jennifer L. Eigenbrode of NASA's Goddard Space Flight Center, David E. Brinza of JPL, Gerald Weigle of SwRI, Stephan Böttcher of Christian Albrechts University , Eckart Böhm of Christian Albrechts University, Soenke Burmeister of Christian Albrechts University, Jingnan Guo of Christian Albrechts University, Jan Köhler of Christian Albrechts University, Cesar Martin of Christian Albrechts University, Guenther Reitz of German Aerospace Center in Cologne, Germany, Francis A. Cucinotta of University of Nevada Las Vegas, Myung-Hee Kim of Universities Space Research Association, David Grinspoon of the Denver Museum of Nature and Science, Mark A. Bullock of SwRI, Arik Posner of NASA, Javier Gómez-Elvira of Centro de Astrobiología in Madrid, Spain, Ashwin Vasavada of JPL, and John P.Grotzinger of JPL, and the MSL Science Team.

Editors:

Images to accompany this story are available at: http://www.swri.org/press/2013/mars-measurements.htm.

For more information, contact Deb Schmid, (210) 522-2254, Communications Department, Southwest Research Institute, PO Drawer 28510, San Antonio, TX 78228-0510.

 

Southwest Research Institute^® (SwRI^®), headquartered in San Antonio, Texas, is a multidisciplinary, independent, nonprofit, applied engineering and physical sciences research and development organization with 11 technical divisions.   

 

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NASA Curiosity: First Mars Age Measurement and Human Exploration Help

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December 09, 2013

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

In a little more than a year on the Red Planet, the mobile Mars Science Laboratory has determined the age of a Martian rock, found evidence the planet could have sustained microbial life, taken the first readings of radiation on the surface, and shown how natural erosion could reveal the building blocks of life. Curiosity team members presented these results and more from Curiosity in six papers published online today by Science Express and in talks at the Fall Meeting of the American Geophysical Union in San Francisco.

The Age of 'Cumberland'

The second rock Curiosity drilled for a sample on Mars, which scientists nicknamed "Cumberland," is the first ever to be dated from an analysis of its mineral ingredients while it sits on another planet. A report 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 of earlier estimates for rocks in Gale Crater, where Curiosity is working.

"The age is not surprising, but what is surprising is that this method worked using measurements performed on Mars," said Farley. "When you're confirming a new methodology, you don't want the first result to be something unexpected. Our understanding of the antiquity of the Martian surface seems to be right."

The analysis of Cumberland from a sample drilled by Curiosity was a fundamental and unprecedented 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 of an isotope of potassium as it slowly changes into argon, an inert gas. Argon escapes when a rock is melted. This dating method measures the amount of argon that accumulates when the rock hardens again.

Before they could measure rocks directly on Mars, scientists estimated their ages by counting and comparing the numbers of impact craters on various areas of the planet. The crater densities are correlated with ages based on comparisons with crater densities on the moon, which were tied to absolute 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 of the 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 million years. 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 a pattern of windblown sand chewing away at relatively thick layers of rock. The eroding layer forms a retreating vertical face, or scarp.

"The exposure rate is surprisingly fast," Farley said. "The place where you'll find the rocks with the youngest 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 whether organic chemicals are preserved from ancient environments. Organic chemicals are building blocks for 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. "We detect organics but can't rule out that they might be brought along from Earth." Curiosity detected higher amounts in Cumberland than it did in in either test runs with Martian soil samples or analysis of empty sample cups. Increasing the amount of rock powder in the test cup increased the amount of organic content detected.

Favorable for Life

Ming is the lead author of a new report about a site called "Yellowknife Bay." The team reported 10 months ago that the first rock Curiosity drilled there, nicknamed "John Klein," yielded evidence that met 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 not too acidic or salty, and an energy source. The energy source is a type used by many rock-eating microbes on Earth: a mix of sulfur- and iron-containing minerals that are ready acceptors of electrons, 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 environment that could have supported life, but it also has provided evidence habitable conditions existed more recently 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 for evidence of life on Mars by improving insight about how erosion may expose buried clues of molecular building blocks of life.

New estimates of when habitable conditions existed at Yellowknife Bay and how long they persisted come from details of rocks' composition and layering. It is thought that Mars had enough fresh water to generate clay minerals -- and possibly support life -- more than 4 billion years ago, but that the planet underwent drying that left any remaining liquid water acidic and briny. A key question was whether 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 water and deposited.

Scott McLennan of Stony Brook University in Stony Brook, N.Y., and co-authors found that chemical elements in the rocks indicate the particles were carried from their upstream source area to Yellowknife Bay and that most chemical weathering occurred after they were deposited. The loss of elements that leach easily, such as calcium and sodium, would be noticeable if the weathering that turns some volcanic minerals into clay minerals had happened upstream. Scientists did not notice such leaching.

David Vaniman of the Planetary Science Institute in Tucson, Ariz., and co-authors found supporting evidence in a separate mineral analysis of sedimentary rocks at Yellowknife Bay. They noticed a lack of olivine and an abundance of magnetite, which suggests the rocks turned to clay after they washed 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 rich environments where you find smectites on Earth."

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

"This habitable environment existed later than many people thought there would be one," Grotzinger said. "This has global implications. It's from a time when there were deltas, alluvial fans and other signs 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 have washed in from older deposits. Now, we know the clay minerals could be produced later, and that gives us many locations that may have had habitable environments, too."

Research suggests habitable conditions in the Yellowknife Bay area may have persisted for millions to 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 veins deposited by underground water into fractures in the rock. The thickness of observed and inferred tiers of rock layers provides the basis for estimating long duration, and the discovery of a mineral energy source for underground microbes favors habitability throughout.

Implications for Human Explorers

Today's reports include the first measurements of the natural radiation environment on the surface of Mars. Cosmic rays from outside our solar system and energetic particles from the sun bombarded the surface at Gale Crater with an average of 0.67 millisieverts per day from August 2012 to June 2013, 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 more than 95 percent of the total came from cosmic rays.

Results from the surface-radiation monitoring provide an additional piece of the puzzle for projecting the total round-trip radiation dose for a future human mission to Mars. Added to dose rates Curiosity measured during its flight to Mars, the Mars surface results project a total round-trip dose rate for a future 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 cancer risk. Exposure to a dose of 1,000 millisieverts is associated with a 5 percent increase in risk for developing 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 the National Academies to address the ethics, principles and guidelines for health standards for long duration and exploration spaceflight missions.

The radiation detected by Curiosity is consistent with earlier predictions. The new data will help NASA scientists and engineers create better models to anticipate the radiation environment human explorers 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're continuing to monitor the radiation environment and seeing the effects of major solar storms on the surface at different times in the solar cycle, will give additional important data. Our measurements also tie into Curiosity's investigations about habitability. The radiation sources that are concerns for human 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 (5 centimeters), the depth of Curiosity's drill, Hassler estimated they would be depleted up to 1,000-fold in 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 been exposed 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 be present in Cumberland to be detectable. Even if Mars has never supported life, the planet receives organic molecules delivered by meteorites, which should leave a detectable trace.

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

For more information about the mission, visit: http://www.jpl.nasa.gov/msl , http://www.nasa.gov/msl and http://mars.jpl.nasa.gov/msl

Guy Webster 818-354-6278
Jet Propulsion Laboratory, Pasadena, Calif.
guy.webster@jpl.nasa.gov

Dwayne Brown 202-358-1726
Headquarters, Washington
dwayne.c.brown@nasa.gov

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Rover results include first age and radiation measurements on Mars

Dec. 9, 2013 at 3:07 PM   |   

This mosaic of images from the Mast Camera (Mastcam) instrument on NASA's Curiosity Mars rover shows a series of sedimentary deposits in the Glenelg area of Gale Crater, from a perspective in Yellowknife Bay looking toward west-northwest. Photo: NASA

PASADENA, Calif., Dec. 9 (UPI) -- The U.S. space rover Curiosity is providing critical information about Mars' past and present to help plan future missions, NASA officials said.

In a little more than a year on Mars, the unmanned mobile science laboratory determined the age of a martian rock, found evidence the planet could have sustained microbial life, took first readings of radiation on the surface, and showed how natural erosion could reveal the building blocks of life, NASA said in a release.

Information about the scientific finds as well as other information gleaned from Curiosity was presented Monday online by Science Express and in talks at the fall meeting of the American Geophysical Union in San Francisco.

The data on radiation will help NASA scientists and engineers create better models to anticipate the radiation environment human explorers will face, NASA said.

Curiosity's first readings of radiation hazards at Mars' surface will help in planning human missions to the Red Planet, NASA said. Other findings will guide the search for evidence of life on Mars by improving insight about how erosion may have affected molecular life.

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

NASA's Jet Propulsion Laboratory in Pasadena, Calif., built Curiosity and manages the mission.

 

© 2013 United Press International, Inc. All Rights Reserved. 

 

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Radiation on Mars 'Manageable' for Manned Mission, Curiosity Rover Reveals

By Mike Wall, Senior Writer   |   December 09, 2013 12:01pm ET

NASA's Mars rover Curiosity took this self-portrait, composed of more than 50 images using its robotic arm-mounted MAHLI camera, on Feb. 3, 2013. The image shows Curiosity at the John Klein drill site. A drill hole is visible at bottom left. Credit: NASA/JPL/MSSS/Marco Di Lorenzo/Ken Kremer View full size image

The risk of radiation exposure is not a show-stopper for a long-term manned mission to Mars, new results from NASA's Curiosity rover suggest.

A mission consisting of a 180-day cruise to Mars, a 500-day stay on the Red Planet and a 180-day return flight to Earth would expose astronauts to a cumulative radiation dose of about 1.01 sieverts, measurements by Curiosity's Radiation Assessment Detector (RAD) instrument indicate.

To put that in perspective: The European Space Agency generally limits its astronauts to a total career radiation dose of 1 sievert, which is associated with a 5-percent increase in lifetime fatal cancer risk. [Mars Radiation Threat to Astronauts Explained (Infographics)]

Humans traveling beyond the protection of Earth's atmosphere and magnetic field risk radiation-caused cancers and other diseases. See how space radiation threatens astronauts in this full infographic.
Credit: Karl Tate, SPACE.com Infographics Artist

"It's certainly a manageable number," said RAD principal investigator Don Hassler of the Southwest Research Institute in Boulder, Colo., lead author of a study that reports the results today (Dec. 9) in the journal Science.

A 1-sievert dose from radiation on Mars would violate NASA's current standards, which cap astronauts' excess-cancer risk at 3 percent. But those guidelines were drawn up with missions to low-Earth orbit in mind, and adjustments to accommodate trips farther afield may be in the offing, Hassler said.

"NASA is working with the National Academies' Institute of Medicine to evaluate what appropriate limits would be for a deep-space mission, such as a mission to Mars," Hassler told SPACE.com. "So that's an exciting activity."

The new results represent the most complete picture yet of the radiation environment en route to Mars and on the Red Planet's surface. They incorporate data that RAD gathered during Curiosity's eight-month cruise through space and the rover's first 300 days on Mars, where it touched down in August 2012.

The RAD measurements cover two different types of energetic-particle radiation — galactic cosmic rays (GCRs), which are accelerated to incredible speeds by far-off supernova explosions, and solar energetic particles (SEPs), which are blasted into space by storms on our own sun.

RAD's data show that astronauts exploring the Martian surface would accumulate about 0.64 millisieverts of radiation per day. The dose rate is nearly three times greater during the journey to Mars, at 1.84 millisieverts per day.

But Mars' radiation environment is dynamic, so Curiosity's measurements thus far should not be viewed as the final word, Hassler stressed. For example, RAD's data have been gathered near the peak of the sun's 11-year activity cycle, a time when the GCR flux is relatively low (because solar plasma tends to scatter galactic cosmic rays).

Curiosity's radiation measurements should help NASA plan out a manned mission to Mars, which the space agency hopes to pull off by the mid-2030s, Hassler said. And they should also inform the search for signs of past or present life on the Red Planet — another top NASA priority.

For example, the new RAD results suggest that microbial life is unlikely to exist right at the Martian surface, Hassler said. But future missions may not have to drill too deeply underground to find pockets of Mars life, if it ever existed.

"These measurements do tell us that we think it could be viable to find signs of possible extant or past life as shallow as 1 meter deep," Hassler said.

The new study is one of six papers published in Science today that report new results from Curiosity. Most of the other studies present evidence that the rover has found an ancient freshwater lake that could have supported microbial life for tens of thousands, and perhaps millions, of years.

 

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