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Cluster spacecraft takes first look at acceleration processes driving aurorae

Aurorae are caused by highly energetic charged particles normally held in space by Earth's magnetic field, colliding with Earth's upper atmosphere.
Provided by the Royal Astronomical Society, United Kingdom
Auroral oval
Image of the auroral oval taken by the IMAGE spacecraft in ultraviolet.
FUV team/NASA
April 12, 2010
Using the Cluster spacecraft, scientists from University College London (UCL) have made the first direct observations of charged particles that lead to some of the brightest aurorae.

Aurorae, or northern and southern lights, are caused by highly energetic charged particles normally held in space by Earth's magnetic field, colliding with Earth's upper atmosphere. As these high-energy particles collide with molecules in the atmosphere, they lose energy, causing the atmospheric molecules to glow and heat the atmosphere. The result is spectacular displays of shimmering curtains of red, green, and blue light normally seen above the polar regions.

Despite their frequent occurrence, there are still many questions regarding the physical processes behind aurorae. The particles that excite an aurora are accelerated up to high energies in a region extending to around 31,000 miles (50,000 kilometers) above the atmosphere. By understanding the accelerating processes in this region, scientists hope to further understand the aurorae.

Launched in 2000, the joint European Space Agency (ESA) and NASA Cluster mission consists of four identical spacecraft flying in a close formation around Earth. Each spacecraft carries a suite of instruments to study the charged particles and electromagnetic fields in the space environment around Earth known as the magnetosphere. The multipoint perspective of the Cluster spacecraft allows scientists to build up a 3-D picture of the magnetosphere.

Colin Forsyth has been leading an international team hoping to directly measure the acceleration of charged particles above the aurora. He has uncovered data from the Plasma Electron And Currents Experiment (PEACE) showing this acceleration in action.

"The Cluster spacecrafts have been maneuvered so that one of them was at a higher altitude than the others when they passed over the auroral regions," said Forsyth. "We were then able to simultaneously measure the particle energies at different heights and, thus, their acceleration. These exciting new results will give us new insight into the accelerating processes and the transfer of energy from the magnetosphere into the atmosphere".

Forsyth and his team aim to link these and similar observations to those of large-scale processes in the magnetosphere and detected on the ground in the auroral regions. This could be a key factor in understanding how energy from the magnetosphere affects the Earth's atmosphere.
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