Invisible sculpture surrounds Earth
October 4, 2012
Thousands of miles above the atmosphere, a gigantic sculpture surrounds our planet.
The sculpture is not solid, but is made of electrically-charged, sub-atomic particles — bits and pieces of busted-up atoms.
Magnetize an iron needle and hang it by a thread to make a compass. The needle swings to point, roughly, north/south. The needle seeks, not Earth’s geographic poles — true north and south — but her magnetic poles. The magnetized needle aligns with Earth’s magnetic field.
Rub a stick-pen briskly through your very dry hair, then move the pen just over your arm, without touching a hair. Rubbing the pen gives it an electric charge, and you can see — even feel — the hair on your arm rise in response to the pen’s electric field.
The radiation belts are a death trap — even for things that never lived.
Electrically charged sub-atomic particles also respond to electric and magnetic fields. The picture on an old-fashioned TV tube is painted by a beam of such particles, steered by such fields.
The charged particles that make up the giant sculpture surrounding Earth are worked and re-worked by electric and magnetic fields generated by Earth’s electromagnetic metal core — by the sun — by lightning bolts — by electric currents that course over our heads.
Working with and against each other, the fields mold Earth’s magnetosphere, the region of space dominated by Earth’s magnetic field, a region that stretches out millions of miles.
Even as they are molded by these fields, the charged particles — the “clay” — push and pull back on the fields (think of pushing two magnets together). The “clay” re-shapes itself, and re-shapes the fields, tweaking the sculptors that sculpt it.
Electric and magnetic fields don’t just shape the magnetosphere; they pump energy into its particles, accelerating them to velocities close to the speed of light — relativistic velocities.
Electric and magnetic fields focus these relativistic particles into a region that extends some thousands of miles above the atmosphere — the Van Allen Radiation Belts.
Much as a fast bullet penetrates armor, relativistic particles penetrate the skin of a spacecraft, and anything or anyone within that spacecraft.
Mostly, the International Space Station orbits below the radiation belts. But Earth’s magnetic field is off-center, pushing the radiation belts low over the South Atlantic. As they pass through the South Atlantic Anomaly, ISS astronauts hunker down in a part of the space station that provides the most shielding.
The radiation belts are a death trap — even for things that never lived. Satellites passing through the South Atlantic Anomaly regularly turn off their electronics, lest the radiation damage their logic circuits.
If possible, spacecraft avoid the radiation belts entirely.
The sun’s magnetic cycle should peak, shortly after its sunspots peak, sometime in the next couple of years. During that peak, the sun’s magnetic field most actively sculpts Earth’s magnetosphere.
A pair of twin spacecraft have just launched, to study how Earth’s radiation belts are sculpted, how their particles are energized, especially, to learn why a sun-triggered geomagnetic storms — major disruptions of electric and magnetic fields — sometimes energize the belts, sometimes de-energize them, sometimes do nothing.
For the next two years, the Radiation Belt Storm Probes — their electronics shielded by extra-thick walls — will not avoid the radiation belts, but will live in them.
Al Stahler’s science programs can be heard on KVMR (89.5 FM). He teaches classes to students of all ages, and may be reached at firstname.lastname@example.org