Solar Superstorms and Radiation
Approximately three months after the crew of Apollo 16 returned from the moon, the sun sent out an enormous explosion from its surface, spewing out radiation and billions of charged particles toward the Earth. This solar storm – one of the largest and most dangerous to occur during the Space Age – thankfully did not occur during Apollo 16 and Apollo 17, which launched four months later.
Solar storms and the radiation they create are one of the biggest obstacles to long-term space travel. Outside the Earth’s protective magnetic fields, astronauts are exposed to far more radiation than they normally experience. Solar flares and other bursts from the sun’s surface generate massive amounts of dangerous X-rays and heavy charged particles that can penetrate into the cells of living creatures, damaging DNA and leading to increased risk of cancer.
Had astronauts been en route to or on the surface of the moon during the 1972 “superstorm” — or similar events in 1956 and 1989 — they would have experienced massive doses of radiation. Their skin would have burned, blistered, and peeled and the radiation penetrating their bones would have caused nausea and vomiting. In all likelihood, they would have been killed.
NASA is required by law to protect its crew from such events and also the longer-term effects of radiation in space. Cumulative exposure in low-Earth orbit – where astronauts receive more radiation than even people working near nuclear reactors on Earth — increases the risk of developing cancer. Since only 24 men have ever traveled beyond low-Earth orbit, the long-term effects of radiation exposure outside the planet’s magnetic field are still largely unknown.
NASA guidelines estimate that males should spend at most 268 days in space and females at most 159 days in space to remain below a three percent chance of contracting cancer over their lifetime. A potential Mars mission would take at least 520 days round-trip, during which a dangerous solar flare could occur.
Major solar storms have been relatively rare during the last century, though this may not be the case in the future. Data from polar ice indicate that we are living through a relatively mild period of solar activity, which may pick up and cause storms larger than even the largest recorded episode – the 1859 Carrington event – which was approximately four times larger than the deadly 1972 storm.
Solar astronomers are hard at work creating better models to help predict such events. Faster computers and increased monitoring might make it possible to forecast solar weather by as much as several weeks in advance. If regular travel to the moon and back ever happens, such data would be extremely useful.
Image: Composite of multiple solar flares bursting from the sun. JAXA/Hinode