The Mars mystique

Curiosity is gathering information, too, that might one day be useful to architects of a human mission. Even as the rover scours Gale Crater for signs that it might once have boasted an environment capable of supporting life, it is measuring radiation levels at the surface. In fact, the instrument responsible for the measurements, known as the Radiation Assessment Detector (RAD), has been monitoring radiation levels since the craft left Earth.

"One of our objectives is to make precursor measurements to help in the planning for future human exploration," notes Don Hassler, a physicist at the Southwest Research Institute in Boulder, Colo., and the lead scientist on the instrument, which was paid for by NASA's human-exploration program.

The exposure of space travelers to radiation is one of the major impediments to a mission to Mars. On Earth, humans are shielded from cell-damaging rays by the atmosphere. But astronauts on a prolonged planetary mission would be exposed to the combined effects of cosmic rays, which stream in from all directions from sources outside the solar system, and particles emitted from the sun, which come from steady solar winds and intense solar storms.

RAD gathered data on the intensity level of both sources during its seven-month journey to Mars – including bursts from five solar storms. "That was fortuitous from our point of view because it gave us an opportunity to characterize the effect of those," Dr. Hassler says.

The research could prove crucial in designing shielding for a spacecraft or for planning the right timing for a future Mars mission – when to go during the sun's 11-year sunspot cycle that would be least dangerous to astronauts.

While spacecraft could be lined to prevent radiation from reaching crew members, some rays are always going to get through. Thus another solution scientists are looking at to limit radiation exposure is reducing the time it takes to get to Mars. "That's the one where maybe some breakthrough is waiting to be made in propulsion that gets you there faster," says Cary Zeitlin, a RAD project scientist.

Assuming scientists opt for using NASA's announced 2020 rover to begin a program dedicated to returning soil and rock samples from Mars, that, too, would provide information to inform future human exploration. Late last month, NASA formally asked scientists to propose experiments the rover would carry out. At its most fundamental level, a sample-return program represents a scaled-down dry run for the sequence of missions needed to send humans.

"It's pretty simple," says John Grunsfeld, NASA's associate administrator for the science mission directorate. "If you can send a mission to Mars, acquire a sample, and return that sample back to Earth, that's a good model for sending a human to Mars and returning that human to Earth."

A sample-return program also could help avoid a debate that nearly squelched the Apollo moon program. The concern centered on viruses astronauts might bring back – something people worry even more about with travelers to Mars.

"A lot of planetary protection people were dead-set against it [sending an astronaut to the moon] and could have blocked the lunar exploration program," notes Mount Holyoke's Dyar, who earned her PhD studying lunar samples. "We were very close on that one."

A sample return program for Mars would allow the most precise analysis possible, from multiple labs, to hunt for signs of organic molecules and better understand the environment to which astronauts would be exposed.

"To me, the holy grail is always gonna be: Return samples," she says.

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