Spacecraft return Sun panoramas

The Stereo orbiters, which are nearing their final positions, will study violent solar eruptions known as Coronal Mass Ejections (CMEs).

CMEs hurl energetic particles at Earth that can disrupt power grids and satellite communications.

Stereo will give scientists information they need to forecast "space weather".

The new panoramic views, which stretch from the Sun to the Earth, are created by combining images from a suite of telescopes onboard the two spacecraft. Their data will allow scientists to track "solar fronts".

"The new view from the Stereo spacecraft will greatly improve our ability to forecast the arrival time of severe space weather," said Dr Russell Howard, principal investigator of Stereo's Sun-Earth Connection Coronal and Heliospheric Investigation (Secchi).

"Previous imagery did not show the front of a solar disturbance as it travelled toward Earth, so we had to make estimates of when the storm would arrive. These estimates were uncertain by a day or so.

"With Stereo, we can track the front from the Sun all the way to Earth, and forecast its arrival within a couple hours."

CMEs erupt when "loops" of solar material lifting off the Sun suddenly snap, throwing a high-temperature (hundreds of thousands of degrees) plasma into space.

The plasma is made up of electrons and ions of hydrogen and helium. A CME will typically contain a billion tonnes of matter and move away from the Sun at about 400km/s.

Much of the time, these outbursts are directed away from the Earth, but some inevitably come our way.

When they do, the particles, and the magnetic fields they carry, can have highly undesirable effects. They have been known to disrupt the radio communications of aircraft, and even "fry" satellite electronics.

The Stereo (Solar TErrestrial RElations Observatory) spacecraft were sent into space on 25 October 2006, and are currently moving into their prime observation positions.

One probe has been put just ahead of the Earth as it moves around the Sun; the other is stationed just behind. The separation between the orbiters allows them to construct 3D images of the Sun-Earth system.

Scientists will use the 3D images to study the structure of CME clouds and to see how they change as they move through space.

"Right now, we don't know where CMEs slow down, why they slow down, or what forces cause them to slow down," said Dr Howard.

"The new views from Stereo are like having a curtain lift from our eyes - they are extraordinarily instructive."

The UK has major interest in the mission, having built the camera detectors on all the imaging instruments. It also delivered a Heliospheric Imager (HI) for each platform. This instrument is used to follow the progress through space of a CME cloud by tracing its reflected light.

Dr Chris Davis, a member of the UK Stereo team from CCLRC's Rutherford Appleton Laboratory, said: "Every new image from Stereo provides us with further detail about the properties of CMEs forever, adding to our knowledge. It is exciting to think that the best images, providing a 3D view of the Sun, are yet to come."

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Nasa - Stereo
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