NASA's twin Solar Terrestrial Relations Observatory, or STEREO, spacecraft are providing the unique scientific tool to study these ejections as never before. Launched in October 2006, STEREO's nearly identical observatories can make simultaneous observations of these ejections of plasma and magnetic energy that originate from the sun's outer atmosphere, or corona. The spacecraft are stationed at different vantage points. One leads Earth in its orbit around the sun, while the other trails the planet.
Using three-dimensional observations, solar physicists can examine a CME's structure, velocity, mass, and direction in the corona while tracking it through interplanetary space. These measurements can help determine when a CME will reach Earth and predict how much energy it will deliver to our magnetosphere, which is Earth's protective magnetic shield.
"Before this unique mission, measurements and the subsequent data of a CME observed near the sun had to wait until the ejections arrived at Earth three to seven days later," said Angelos Vourlidas, a solar physicist at the Naval Research Laboratory in Washington. Vourlidas is a project scientist for the Sun Earth Connection Coronal and Heliospheric Investigation, STEREO's key science instrument suite. "Now we can see a CME from the time it leaves the solar surface until it reaches Earth, and we can reconstruct the event in 3D directly from the images."
