Space weather, also known as solar weather, refers to the light, energy and particles that stream off of the sun. The so-called solar wind is a constant stream of particles that stretches all the way beyond Pluto, creating an envelope around the solar system. The sun also releases sporadic, intense bursts of light (solar flares) and eruptions of charged particles (coronal mass ejections, or CMEs). When these particles strike Earth’s magnetic field, they can create the natural light show known as the auroras.

The particles released by the sun are a type of radiation, and can cause physical harm to humans. People on Earth are protected by Earth’s atmosphereand its magnetic field, but without proper shielding, astronauts are exposed to these harsh weather events.

Scientists are interested in finding out exactly how much radiation astronauts will be exposed to during a trip to the Red Planet and once they get there, John Grunsfeld, a former astronaut who now serves as associate administrator of NASA’s Science Mission Directorate, said at the event. (Mars doesn’t have a magnetic field that protects it from space radiation, and its atmosphere is much thinner than Earth’s.) Specific questions need to be answered about when astronauts are most vulnerable to space radiation, how that dose will affect the human body over long periods of time, and how to mitigate the health risks of space radiation, he said. (Some of those questions were answered by the rovers that NASA has sent to Mars.)

On most days, astronauts in space receive a steady dose of radiation from the solar weather and from radiation coming from outside the solar system. The International Space Station is equipped with shielding to keep that dose as low as possible, but astronauts are more vulnerable during spacewalks, when they are protected only by their suits.

Solar flares and CMEs from the sun could deliver potentially devastating doses of radiation to space travelers. Sections of the space station have additional radiation shielding to protect occupants during these solar events. According to Grunsfeld, a solar storm peppered the lunar surface with a radiation shower between the Apollo 16 and Apollo 17 missions to the moon in the early 1970s. If astronauts had been on the moon at the time, they might have received a radiation dose high enough to require immediate medical attention, he said. Humans traveling to Mars will have to deal with these threats as well.

“We have a plan that looks at all of the risks of going to Mars, and a big part of it is environmental modeling, monitoring and prediction of solar flares and solar events,” Grunsfeld said. “It’s not quite as advanced as terrestrial weather [monitoring] now, where we can see a hurricane and try to predict its path and see where it will go. The sun is much more complicated, so there’s a lot of knowledge that we still need to gain.”

That knowledge is coming from many different places. NASA has a fleet of satellites studying the sun, including the Solar Terrestrial Relations Observatory (STEREO), which has been in operation for 10 years. STEREO consists of two satellites that orbit on opposite sides of the sun, which essentially provides the satellites with depth perception, and the ability to determine where solar eruptions are coming from and where they are heading. STEREO can let people on Earth know when a CME or solar flare is headed their way.