Crewed missions to Mars is an essential goal for NASA, but researchers are started to understand and characterize the radiation hazards that could make such missions risky.

In a new study published online in the journal Space Weather, associate professor Nathan Schwadron of the UNH Institute for the Study of Earth, Oceans, and Space (EOS) and the department of physics confirmed that due to an abnormal and extended lack of solar activity, the solar wind is exhibiting low densities and magnetic field strengths, which causes dangerous levels of hazardous radiation to pervade the space environment.

"The behavior of the sun has recently changed and is now in a state not observed for almost 100 years," says Schwadron, lead author of the paper and principal investigator for the Cosmic Ray Telescope for
the Effects of Radiation (CRaTER) on NASA's Lunar Reconnaissance Orbiter (LRO), according to a University of New Hampshire press release

He added that throughout most of the space age, the sun's activity showed a clockwork 11-year cycle, with approximately six- to eight-year lulls in activity, followed by two- to three-year periods when the sun is more active.

"However, starting in about 2006, we observed the longest solar minimum and weakest solar activity observed in the space age," Schwadron said.

These conditions brought about the highest intensities of galactic cosmic rays seen since the beginning of the space age, and created worsening radiation hazards that could threaten future deep-space missions.

"While these conditions are not necessarily a showstopper for long-duration missions to the moon, an asteroid, or even Mars, galactic cosmic ray radiation in particular remains a significant and worsening factor that limits mission durations," says Schwadron.

The study is the capstone article in the pace Weather CRaTER Special Issue, which provides "comprehensive findings on space-based radiation as measured by the UNH-led detector," according to the release.

Data provided in the study is critical information on the radiation hazards that will be faced by astronauts during deep space missions, like ones to Mars. 

 Click here to view the papers.

"These data are a fundamental reference for the radiation hazards in near Earth 'geospace' out to Mars and other regions of our sun's vast heliosphere," says Schwadron, according to the release.

At the heart of CRaTER is "tissue equivalent plastic," a material that is used as a stand in for human muscle capable of gauging radiation dosage.

Ionizing radiation from galactic cosmic rays and solar energetic particles is still a big challenge to long-duration crewed missions to deep space. Humans face a number of consequences ranging from acute effects (radiation sickness) to long-term effects including cancer induction and damage to organs including the heart and brain, according to the release.

High radiation levels seen during the sun's last minimum cycle limits the allowable days that astronauts can be behind spacecraft shielding, according to the release. Thanks to the trend of reducing solar output, the allowable days in space for astronauts is dropping and estimated to be 20 percent lower in the coming solar minimum cycle, compared to the last minimum cycle.

Study coauthors on the capstone paper include Colin Joyce, Marty Quinn, Charles Smith, Sonya Smith, Harlan Spence, and Jody Wilson. 

The CRaTER investigation is a collaboration with team members at UNH, the University of Tennessee at Knoxville, Southwest Research Institute, Harvard-Smithsonian Center for Astrophysics, The Aerospace Corporation, the University of Michigan, and NASA Goddard Spaceflight Center.

Support for this research comes from NASA's LRO/CRaTER mission, and NASA'S Earth-Moon-Mars Radiation Environment Module and Corona-Solar Wind Energetic Particle Acceleration projects.

Other support comes from the National Science Foundation's Frontiers in Earth-System Dynamics program.

The NASA Goddard Space Flight Center in Greenbelt, Md. developed and manages the LRO mission. LRO's current science mission is implemented for NASA's Science Mission Directorate, according to the release.

NASA's Exploration Systems Mission Directorate sponsored LRO's initial one-year exploration mission that wrapped up back in September 2010.  

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