Brussels, 04 Aug 2005
A team of researchers from the UK and France have used two spacecraft to trace the journey of an eruption on the sun to its arrival at planet Earth.
The team, led by scientists from the University College London (UCL) were interested in finding out how the magnetic field of a 'coronal mass ejection ' (CME) changed on its way to Earth. They used the European Space Agency (ESA) and NASA Solar and Heliospheric Observatory (SOHO) and ESA's Cluster spacecraft to track its progress.
'There's been much speculation about the shape of the magnetic field and how it might change on its journey from the Sun to Earth,' said Dr Louise Harra of UCL Mullard Space Science Laboratory. 'Using complementary satellites we have been able to see that the magnetic field changes very little on its journey,' she said.
Triggered by an explosion on the Sun involving several million times the amount of energy in a nuclear bomb, CMEs are blasts of gas that could, in theory, engulf Earth. They are caused by the collision of loop-like magnetic field lines with different polarities on the Sun's surface.
Earth is normally protected by a magnetic field that forms a magnetosphere. But when the CME's fields collide directly with it they can cause geomagnetic storms. In extreme cases this can lead to electrical power outages and damage to communications networks and satellites. If scientists are to predict storms, they need to be able to identify coronal mass ejections that are directed towards Earth at the moment when they leave the Sun. They must also understand how the CMEs evolve.
A CME was detected in January 2004 by the SOHO spacecraft, which then identified the source of the ejection. Two days later, on its journey to Earth, the magnetic field passed by ESA's four Cluster spacecraft, which was able to record the speed and direction of the field. Similar measurements were also made by NASA's ACE spacecraft.
'SOHO and Cluster spacecraft are ideally suited to working together,' said Dr Harra. 'SOHO 'sees' the explosions form the Sun and Cluster 'feels' them. Our next step is to predict the eruption of storms on the Sun,' she added.
SOHO is stationed 1.5 million kilometres away from the Earth, from where it constantly watches the Sun. Its discoveries to date have included complex currents of gas flowing beneath the visible solar surface, and rapid changes in the pattern of magnetic fields.
The Cluster spacecraft have spent several years passing in and out of Earth's magnetic field. Their mission is to complete the most detailed investigation yet made of the ways in which the Sun and the Earth interact.