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Sun may delay plans for sending humans to Mars

Less solar activity indicates a weaker magnetic field on the sun. A weak field lets cosmic rays into the solar system, posing a radiation hazard for astronauts.

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View larger. | This illustration depicts the heliosphere, or sphere of the sun’s magnetic influence. Outside this sphere, there’s a large increase in galactic cosmic rays. Illustration via AGU

The human dream of travel to Mars and beyond seems closer than it’s ever been. Several nations and private organizations are developing plans to send humans to Mars in the coming decades. But a new study announced by the American Geophysical Union on October 21, 2014 suggests that these plans might need to be delayed, or at least significantly altered. The reason? Increasing levels of cosmic radiation spurred by decreasing activity on our sun.

When the sun is active, its magnetic field intensifies. At such times, the sun’s magnetic field deflects galactic cosmic rays away from our solar system. A less active sun indicates a weakened solar magnetic field. In other words, more cosmic rays are zipping through our solar system, posing a radiation hazard for astronauts.

The sun’s activity has been weak in recent years, and scientists expect it to decline still more. The new study suggests that, as this happens, the number of days humans could safely spend in deep space might decrease by about 20 percent.

This prediction is not unexpected. Our sun has a regular cycle of activity, with peaks and valleys approximately every 11 years. At the low point of the current solar system (cycle #24) around 2009, the measured amount of cosmic rays hit a space-age high. In 2009, cosmic ray intensities increased 19% beyond anything scientists had seen in the previous 50 years. At that time, some scientists were speaking of re-thinking how much radiation shielding astronauts would need to take with them on deep-space missions. Read more about increased cosmic rays at the low point of the current solar cycle.

Since then, the current solar cycle has continued to be unusual. This past year should have been the peak, but there many fewer sunspots and much less activity than at previous peaks.

A major decrease in solar activity is predicted to occur for the next solar cycle (cycle #25). Such a decrease could make manned journeys to Mars more risky with respect to the health of the crews.

The new research finds that, during periods of low solar activity, a 30-year-old astronaut can spend roughly one year in space before the constant bombardment by cosmic rays pushes the risk of radiation-induced cancer above current exposure limits.

That’s just enough time to get to Mars and back. It doesn’t leave much time for exploration, and, if we can’t explore … should we go?

Bottom line: If the sun’s activity continues to weaken, as many scientists predict, future missions to carry humans to Mars would be far more dangerous.

Read more via the American Geophysical Union

Deborah Byrd

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