* Astronomy

Oxygen is constantly leaking out of Earths atmosphere and into space. Now, ESAs formation-flying quartet of satellites, Cluster, has discovered the physical mechanism that is driving the escape. It turns out that the Earths own magnetic field is accelerating the oxygen away.

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In a paper published recently in the journal Nature Physics, an international team of space scientists led by researchers from the University of New Hampshire present findings on the first experimental evidence that points in a new direction toward the solution of a longstanding, central problem of plasma astrophysics and space physics.
The mystery involves electron acceleration during magnetic explosions that occur, for example, in solar flares and substorms in the Earths magnetosphere the comet-shaped protective sheath that surrounds the planet and where brilliant auroras occur.
During solar flares, accelerated electrons take away up to 50 percent of the total released flare energy. How so many electrons are accelerated to such high energies during these explosive events in our local part of the universe has remained unexplained.
A mainstream theory holds that the mysterious, fast-moving electrons are primarily accelerated at the magnetic explosion site called the reconnection layer where the magnetic fields are annihilated and the magnetic energy is rapidly released. However, physicist Li-Jen Chen of the Space Science Center within the UNH Institute for the Study of Earth, Oceans, and Space discovered that the most powerful electron acceleration occurs in the regions between adjacent reconnection layers, in structures called magnetic islands.
When Chen analysed 2001 data from the four-spacecraft Cluster satellite mission, which has been studying various aspects of Earths magnetosphere, she found a series of reconnection layers and islands that were formed due to magnetic reconnection.

Our research demonstrates for the first time that energetic electrons are found most abundantly at sites of compressed density within islands - Li-Jen Chen .

Another recent theory, published in the journal Nature, has suggested that contracting magnetic islands provide a mechanism for electron acceleration. While the theory appears relevant, it needs to be developed further and tested by computer simulations and experiments, according to the UNH authors.
Until the UNH discovery there had been no evidence showing any association between energetic electrons and magnetic islands. This lack of data is likely due to the fact that encounters of spacecraft with active magnetic explosion sites are rare and, if they do occur, there is insufficient time resolution of the data to resolve island structures.
In the Nature Physics paper, entitled Observation of energetic electrons within magnetic islands, lead author Chen reports the first experimental evidence for the one-to-one correspondence between multiple magnetic islands and energetic electron bursts during reconnection in the Earths magnetosphere.

Our study is an important step towards solving the mystery of electron acceleration during magnetic reconnection and points out a clear path for future progress to be made - Chen. UNH collaborators on the paper include Amitava Bhattacharjee, Pamela Puhl-Quinn, Hong-ang Yang, and Naoki Bessho.

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Enormous bubbles of plasma trapped within Earth's magnetic fields have been fully mapped for the first time.
Scientists now think the bubbles of ionised gas, called convection cells, are strongly affected by pummelling from the sun's solar wind. Future observations of the cells could be used to monitor violent solar outbursts, such as solar flares and coronal mass ejections, which can harm satellites or astronauts in space.

"The results are a great achievement" - Philippe Escoubet, the European Space Agency (ESA) project scientist for the experiments aboard the Cluster satellites.

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A rare, timely conjunction of ground-based instrumentation and a dozen satellites has helped scientists better understand how electrons in space can turn into killers. ESAs Cluster constellation has contributed crucially to the finding.
 Killer electrons are highly energetic, negatively charged particles found in near-Earth space. They can critically, and even permanently, damage satellites in orbit, including telecommunication satellites, and pose a hazard to astronauts.

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