article image

Third radiation belt surprises NASA scientists

Paul Sutherland, Feature writer
Mar 7, 2013, 8:00 UTC

Sen—Twin NASA probes launched last year to study the Earth's protective magnetic shield have surprised scientists by discovering a new radiation belt around our planet.

Previously, two belts of trapped radiation were known to exist, one an inner and one an outer zone. Discovered in 1958 by satellites, they were named the Van Allen Belts after physicist James Van Allen who identified them.

Now NASA's Van Allen Probes - renamed since they were launched in August 2012 as the Radiation Belt Storm Probes - have spotted a third, short-lived, radiation belt around Earth that no one knew could be there.

It was one of the first findings of the missions, thanks to the fact that a particular particle sensor, called the Relativistic Electron Proton Telescope (REPT) instrument, had been turned on swiftly after launch (within three days) at scientists' request.

Artwork showing three radiation belts

Artwork showing three radiation belts. Green represents the spaces between the belts. Credit: NASA/Van Allen Probes/Goddard Space Flight Center

They wanted its observations to overlap with those of another mission called SAMPEX (Solar, Anomalous, and Magnetospheric Particle Explorer), that was on its last legs and about to re-enter Earth's atmosphere.

A recent surge in solar activity had caused the radiation belts to swell and this behaviour was followed by the REPT instrument. Then to scientists' astonishment, they watched as the particles settled settled to form a new, third belt stretching into space.

The new belt did not last long - about four weeks before it was zapped and blown away by a powerful blast of space weather from the Sun. But the fact it existed means scientists must rethink how the radiation belts form and evolve.

Nicky Fox, Van Allen Probes deputy project scientist at the Johns Hopkins University Applied Physics Laboratory, Maryland, said: "Even 55 years after their discovery, Earth's radiation belts still are capable of surprising us. We thought we knew the radiation belts, but we don't."

UK space weather expert Stuart Clark told Sen: "Understanding solar activity and the effects it can have at Earth is one of the most pressing scientific quests of the present day.

"The Van Allen belts were one of the first discoveries of the space age. To only now discover this third temporary belt is extraordinary."

Dr Clark, author of The Sun Kings (Princeton), added: "This is a powerful reminder that we do not understand a lot of what takes place just above our heads. Magnetic effects such as this are a ubiquitous process. We are learning not just about Earth but about the wider universe too.

"The Sun is approaching a peak in its activity this year. It's a weak crescendo yet it can still create whole new radiation belts. It makes you wonder what we’ve been missing for all the decades when the Sun was much more activity."

The twin probes, which each carry an identical set of five instruments, travel in orbits that take them through the two previously known Van Allen Radiation Belts. Their task is to probe space weather, the direct effects of activity on the Sun, which can imperil hundreds of satellites that today's high-tech society relies on for GPS, weather monitoring, communications and TV.

A video about the discovery of the third radiation belt. Credit: NASA