[meteorite-list] SwRI Scientists Publish First Radiation Measurement From the Surface of Mars

[Ron Baalke]

http://www.swri.org/9what/releases/2013/mars-measurements.htm

SwRI scientists publish first radiation measurements from the surface of Mars
Southwest Research Insitute
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.

[Image: graph of radiation surface dose rates]
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."

[Image: chart comparing radiation dose equivalents}
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.