A human presence in space is one day going to mean something more than putting a crew into low Earth orbit or even going to the Moon. But longer journeys — to Mars, to Jupiter’s moons and beyond — count among their many challenges the problem of radiation. To solve it, we’ll have to start closer to home, puzzling out our own local radiation hazards from the Van Allen belts, those regions of high-energy electrons and ions caught within the magnetic field of Earth.
Because electromagnetic waves can accelerate electrons, causing so-called ‘enhancement events’ or surges that are up to a thousand times more dense than the norm. The danger to spacecraft electronics can be acute. A powerful solar storm in 2003, for example, caused instrument damage to several spacecraft and may have been the cause of the loss of two Japanese satellites. We’re learning that we need radiation-hardened systems that can withstand such battering.
The 2003 event — actually two storms that occurred back to back in October and November — began to offer clues to the process. So intense were these storms that part of the Van Allen radiation belt was drained of electrons and reformed much closer to Earth. A theory known as ‘radial diffusion’ suggested how the radiation belts should intensify as they reformed (an effect thought to be driven by solar activity), but that didn’t happen. Scientists using data from the European Space Agency’s Cluster mission were then able to show that very low frequency electromagnetic waves can cause the particle acceleration needed to intensify the belts.
Now a new paper out of Los Alamos National Laboratory looks at how the acceleration process works. Using data from three different satellites, the team measured electron fluxes and converted physical measurements to magnetic coordinates. The study confirmed that localized peaks have to be caused by the acceleration of the electrons by electromagnetic waves. Says Los Alamos’ Yue Chen, lead author of the paper: “Debates on the source of the acceleration have lasted for at least a decade, and this paper finally settles the argument based on observations.”
Which is a start, but the exact nature of the interaction is not yet understood. NASA will launch two missions in 2012 in an attempt to probe how the radiation belts are created and decay, with the goal of producing enough empirical data to aid in the design of future radiation-hardened vehicles, and of providing better forecast models to predict geomagnetic storm activity. The paper is Yue Chen et al., “The energization of relativistic electrons in the outer Van Allen radiation belt,” Nature Physics 1 July 2007. It’s a reminder of how far we have to go in our understanding of even the near-Earth environment, much less such vast radiation wastelands as we’ll find around planets like Jupiter.