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Visions of Sun's great 'belches'

15 April 08 11:14 GMT
By Richard Black
Environment correspondent, BBC News website, Vienna

Nasa's Stereo orbiters have captured stunning new images of spaceborne debris thrown out from the Sun.

The twin spacecraft have seen Coronal Mass Ejections (CMEs) hurling material into a comet, ripping off its tail.

Scientists hope the probes will allow better forecasting of CMEs, which sometimes disrupt communication systems on Earth.

The research was presented at a major science and environment conference in Vienna.

The near-identical Stereo (Solar TErrestrial RElations Observatory) craft orbit the Sun along virtually the same trajectory as the Earth.

One travels ahead of our planet, the other trails behind; and these twin vantage points allow the probes to image in three dimensional detail what happens between the Sun and the Earth.

Instruments on board include the Heliospheric Imagers (HIs) provided by the UK.

"We're able to image CMEs further out away from the Sun than we could before," said Danielle Bewsher from the UK's Rutherford Appleton Laboratory in Didcot.

"You can see them coming from the Sun and travelling through space, and potentially you can actually see them hitting the Earth," she told BBC News after presenting her team's findings at the European Geosciences Union (EGU) conference.

Sting in the tail

A CME begins when a loop of ionised plasma that is raised above the surface of the Sun by its intense magnetic fields suddenly breaks.

This hurls ionised hydrogen and helium into space, sometimes amounting to a billion tonnes of matter.

The Earth is somewhat protected by its magnetic field; but even so, CMEs or "solar burps" have been known to knock out satellite communications equipment, control gear on aircraft and even power grids.

A comet has no such protection. And during the course of last April, Stereo showed scientists in some detail what happens when one of these interplanetary voyagers encounters a solar blast.

As Comet 2P/Encke travels close to the Sun - about one-third of the distance between the Sun and the Earth - it is hit by what seems to be a giant wave, although in reality it is a relatively modest CME travelling at a mere 370km (230 miles) per second.

Its tail appears to be stripped clean off - though this is something of an illusion, according to Professor Christopher Russell from the University of California at Los Angeles (UCLA).

"The plasmoid [the end of the tail] is ripped off, and the rest of the tail is turned round so you don't see it anymore," he told EGU delegates.

Scientists hope that observing and analysing a number of CMEs will yield greater understanding of how they form and how they travel through space.

"We've never known what happened at these distances from the Sun - whether CMEs continued at a constant velocity, or whether they decelerated," noted Dr Bewsher.

"We had to make it up as we went along; and Stereo is filling in the gaps."

The first fruits of the mission have been a long time coming for Volker Bothmer of Goettingen University, in Germany, a member of the team that first proposed Stereo back in 1993.

"It's the Sun in 3D," he said, "and with different viewing angles.

"And it's the first time that we see the whole Sun."

The images collected by the HI instruments during more than a year of observation actually show much more than the Sun.

As they capture all light, they contain a wealth of material about stars as well, which may also prove valuable to astronomers.

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