Thanks to the Solar Terrestrial Relations Observatory (STEREO), astrophysicists are getting an unprecedented three-dimensional view of the sun. The twin satellites are now beaming back their first pictures of explosive events on the solar surface. Slightly separated from each other, the two can image events on the sun’s surface simultaneously, allowing depth perception. Before STEREO, astrophysicists had no way of tracing the front of a solar storm as it traveled from the sun to Earth, so they had to guess when a storm would hit. STEREO’s detailed in-depth view will give them a forecast accurate to within a couple of hours.
One of STEREO’s most important tasks will be tracking solar flares and coronal mass ejections, which pack the force of a billion-megaton nuclear bomb and are the most powerful explosions in the solar system. These turbulent events also send out a burst of solar wind—energetic subatomic particles—that strikes Earth’s magnetic field within 21 hours, creating a geomagnetic storm. That can translate into space weather severe enough to knock out radio communications and satellites, and even overload terrestrial power grids. NASA scientists estimate that a worst-case solar storm could have an economic impact similar to that of a category 5 hurricane or a tsunami: One scenario shows that the cost of lost satellites could be as much as $70 billion. Knowing when such storms are coming helps protect astronauts as well as ground communications: Physicists estimate that a 1989 solar outburst released enough radiation to expose astronauts on the Mir space station to their yearly dose in just a few hours.
“In terms of space weather forecasting, we’re where meteorologists were in the 1950s. They didn’t see hurricanes until the rain clouds were right above them; in our case, we can see storms leaving the sun but have to make guesses and use models to figure out if and when they will impact Earth,” says Michael Kaiser, project scientist for STEREO at NASA’s Goddard Space Flight Center. As the data pour in, these satellites should change all that.