Spacecraft sees solar storm in 3-D; it's the blob!

An artist's reconstruction of an outburst from the sun called a coronal mass ejection (in orange). Data for the illustration were gathered by NASA's STEREO satellites.

Now this is what the twin STEREO-mission spacecraft were designed to do.

Hunting for evidence of a small planet that smacked the Earth and formed the moon is a sideline. (You can read more about that here.) STEREO's day job is to help scientist track enormous outbursts of charged particles from the sun -- outbursts that can wreak havoc on satellites orbiting Earth, as well as threaten the well-being of astronauts on orbit. They can disrupt the electricity grid on Earth. And they trigger hauntingly beautiful auroras.

About-to-be-published results by a team of British scientists suggests that STEREO-like spacecraft are capable of giving Earth at least 24-hour's warning that a so-called coronal mass ejection (CME) is about to arrive.  They base their conclusion on data from the STEREO spacecraft, which tracked one of these ejections from the git-go last December.

First, a word about CMEs.  A CME is the mother of all solar storms. In effect, it's the sun going: Aw, snap! Folks are still trying to figure out the mechanism driving these storms. But in broad brush, the sun's magnetic field stores an enormous amount of energy. At some point, so the thinking goes, the field becomes unstable and unleashes that energy, hurtling blobs of charged particles from the suns corona into space.

These blobs of plasma, with their own magnetic fields, travel through space at speeds ranging from 45,000 miles an hour to more than six million miles an hour.

Typically, these ejections are seen as 2-D images, making it difficult to determine their direction of travel, among other things. STEREO's twin spacecraft -- one orbiting the sun ahead of Earth, the other behind -- are designed to look at the same ejection with spacing wide enough to build a series of 3-D images. Now it's possible to get a bead on its structure, its mass, its velocity, and its direction from the time it leaves the sun until it reaches Earth.

And that's what the British team, led by Chris Davis with the Rutherford Appleton Laboratory in Britain did.  STEREO data provided estimates of the plasma blob's speed and direction. Based on that, researchers predicted the time it should strike the ACE spacecraft. That's a satellite monitoring cosmic rays as well as radiation from the sun. It's located some 932,000 miles from Earth and always in a direct line between the Earth and sun.

And researchers could predict the time the CME should influence Earth.

They scored on both counts. The ACE spacecraft recorded the CME's arrival within a few hours of the predicted time. And magnetometers on Earth recorded a slight but widespread "disturbance in the force" -- Earth's magnetic field -- within a few hours of the time scientists had predicted the CME would smack into Earth's magnetosphere.

Typically, the most space-weather forecasters could say was: The CME will reach Earth in three to seven days. Then folks just hunkered down and waited.

The team is appropriately cautious about drawing sweeping conclusions from one experience.

"This is an exciting result," the team writes in a paper that should be on the streets in a couple of weeks in the journal Geophysical Research Letters. "But a statistical analysis of similar events and a comparison with current models is needed before we can ascertain the effectiveness of such a technique when applied to space-weather forecasting.

Still, it's not a bad start as a proof-of-concept in space weather forecasting. In fact the team dubbed the results "a milestone" for STEREO. The team noted that this is the kind of precision humans will need as they move off Earth and set up operations on the Moon or Mars.

It should provide for some interesting hallway discussions at next month's Space Weather Enterprise Forum. It's being held in Washington, and aims to bring scientists, government officials, and representatives of businesses affected by space weather together to figure out how to get ready for the projected peak in the 11-year cycle of solar activity, currently projected to top out between 2011 and 2012.

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