A breakthrough by a team of British, US and French scientists will helpprotect astronauts, spacecraft and satellites from radiation hazardsexperienced in space.
Reporting in the journal Nature this week, the team describehow their study of rare and unusual space storms provided a uniqueopportunity to test conflicting theories about the behaviour of highenergy particles in the Van Allen radiation belts* - a volatile region12000 miles (19,000 km) above the Earth.
Lead author, Dr Richard Horne of the British Antarctic Survey(BAS) says"Solar storms can increase radiation in the Van Allen belts to levelsthat pose a threat to spacecraft. As modern society relies increasinglyon satellites for business, communications, and security, it isimportant to understand the environment that spacecraft operate in sothat we can help protect our space investment.
"For a long time scientists have been trying to explain whythe number of charged particles inside the belts vary so much. Ourmajor breakthrough came when we observed two rare space storms thatoccurred almost back-to-back in October and November 2003. During thestorms part of the Van Allen radiation belt was drained of electronsand then reformed much closer to the Earth in a region usually thoughtto be relatively safe for satellites.
" When the radiation belts reformed they did not increaseaccording to a long-held theory of particle acceleration. Instead, byusing scientific instruments in Antarctica and on the CLUSTER missionsatellites, we showed that very low frequency radio waves caused theparticle acceleration and intensified the belts.
"This new information will help spacecraft operators and spaceweather forecasters who must predict when satellites and missions aremost at risk from radiation events allowing them to take measures toprotect instruments and systems from damage, and astronauts from risksto their health."
Wave Acceleration of electrons in the Van Allen radiation Belts by Richard B. Horne1, Richard M. Thorne2, Yuri Y. Shprits2,Nigel P. Meredith1, Sarah A. Glauert1, Andy J. Smith1, Shrikanth G.Kanekal3, Daniel N. Baker3, Mark J. Engebretson4, Jennifer L. Posch4,Maria Spasojevic5, Umran S. Inan5, Jolene S. Pickett6 & PierretteM. E. Decreau7 is published this week in the journal Nature.
1 British Antarctic Survey, Madingley Road, Cambridge CB3 0ET, UK.
2Department of Atmospheric and Oceanic Sciences, University ofCalifornia Los Angeles, 405 Hilgard Avenue, Los Angeles, California90095-1565, USA.
3 Laboratory for Atmospheric and Space Physics, University of Colorado,1234 Innovation Drive, Boulder, Colorado 80303-7814, USA.
4 Department of Physics, Augsburg College, Minneapolis, Minnesota 55454, USA.
5 STAR Laboratory, Stanford University, Stanford, California 94305, USA.
6 Department of Physics and Astronomy, University of Iowa, Iowa City, Iowa 52242-1479, USA.
7 LPCE, 3A, Avenue de la recherche scientifique, 45071, Orleans, Cedex 2, France.
* Van Allen radiation belts
The Van Allen radiation belts were the foremost discovery of the spaceage after being detected by the first US satellite Explorer I, whichwas launched during the International Geophysical Year of 1957-58. Theyare composed of energetic charged particles trapped inside the Earth'smagnetic field, which surrounds the Earth like a ring doughnut. Theyvary according to solar activity. Other planets with magnetic fields,such as Jupiter and Saturn, also have radiation belts. At present it isnot known how the radiation belts at the other planets are formed, butthe wave acceleration theory presented here could apply.
The 'old' theory
Until now it was believed that theelectrons within the belts were accelerated by radial diffusion. Thiscan be explained by thinking of the Earth's magnetic field as elasticbands. If the bands are plucked, they wobble. If they wobble at thesame rate as the particles drifting around the Earth then the particlescan be driven across the magnetic field and accelerated. This processis known as radial diffusion and is driven by solar activity. The newresearch presented here shows that this theory is now inadequate.
Antarctica is our 'window on space'.Magnetic space storms damage spacecraft, disrupt power supplies,communications & navigation systems and alter satellite orbits. BASscientists are attempting to predict Space Weather through a betterunderstanding of the complex process that take place when the Earth andSun's magnetic fields meet. BAS scientists use several differenttechnologies to measure variations in the Earth's magnetic field. Datafrom these studies are used in mathematical models to test theoreticalideas. This research makes a major contribution to international globalresearch programmes that involve spacecraft and networks ofground-based scientific instruments.
Whistler mode chorus waves
During magnetic storms verylow frequency radio waves (in the audio range below 20 kHz) aregenerated in space by low energy electrons. The waves can be guidedalong the magnetic field down to the ground in the polar regions. Undersome conditions the waves can accelerate a small number of electrons tovery high energies and trap them in space. These are the particles thatdamage spacecraft. But under other conditions they can drain theradiation belts by dumping energetic particles down into the upperatmosphere and change its chemistry as a result.
British Antarctic Survey is a world leader in research intoglobal issues in an Antarctic context. It is the UK's national operatorand is a component of the Natural Environment Research Council. It hasan annual budget of around£ 40 million, runs eight research programmesand operates five research stations, two Royal Research Ships and fiveaircraft in and around Antarctica. More information about the work ofthe Survey can be found at: www.antarctica.ac.uk
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