WASHINGTON--On 11 January, Earth got a visitor from space: a gigantic cloud of magnetized solar gas. This visitor may have arrived unnoticed to most people, but it didn't slip past the watchdogs at NASA and other space agencies worldwide. Thanks to 20 spacecraft and 30 ground-based facilities in 12 countries, scientists tracked this magnetic cloud in unprecedented detail, NASA announced at a press conference here today.
Coils of magnetic energy burst periodically from the sun, triggering mass ejections of magnetized solar gases. These charged gases can create magnetic "storms" when they slam into Earth's outer atmosphere, which in turn sometimes disrupt power grids. To try to prevent damage to powerlines, experts are hoping to better predict an arriving cloud's impact. But until now, said astronomer Steve Maran of NASA's Goddard Space Flight Center in Greenbelt, Maryland, scientists have been like the blind men trying to scope out an elephant--except "what we're dealing with is an elephant millions of miles long racing by at a million miles an hour."
This time a gauntlet of instruments tracked a cloud 48 million kilometers across from its origin on the sun's surface to its collision with Earth's atmosphere. "This is the first time we have been able to observe something from the very start," said University of Minnesota physicist Barbara Thompson.
On 6 January, the cloud, traveling at 450 kilometers a second, overran the sun-orbiting Solar and Heliospheric Observatory satellite. Other satellites monitored it as it billowed earthward, until ground-based facilities picked up perturbations 4 days later. These measurements showed that the cloud had sent a "pressure pulse" into Earth's magnetosphere--magnetic lines of force reaching from pole to pole far above the atmosphere. The pulse compressed the magnetosphere on Earth's sun side by about one-third, or 23,000 kilometers, said Goddard's Mauricio Pereto, and it created magnetic "substorms" picked up by magnetometers in Greenland and Canada.