Living with a star can be a challenge, especially as
Earthlings extend their reach into space. A Rice University scientist is
contributing to an effort to make life more comfortable for both the people and
satellites sent out there, and provide valuable research for those who remain
planet-bound.
Two Radiation Belt Storm Probes (RBSP) scheduled for launch
from Cape Canaveral, Fla., Aug. 23, 2012, will monitor space weather, from the
normal eddies of particles that flow through what was once thought of as a
void, to the sun’s raging plasma blasts that endanger astronauts, orbiting
electronics, and even the power distribution grid on Earth’s surface.
The probes will do so from elongated orbits that take them
into the heart of the Van Allen Belts, doughnut-shaped regions of high-energy
particles encircling Earth. The two NASA spacecraft will travel through
constantly changing magnetic fields that trap the high-energy particles but
also keep the majority of the harsh radiation of the sun at bay. They’ll back
each other up by gathering data on events from different perspectives to give
researchers a clearer picture than ever of how solar storms affect the belts.
“These two spacecraft have an unprecedented number of
instruments, spanning fields and particles over exceptionally wide ranges,”
says Anthony Chan, a Rice professor of physics and astronomy and part of the Energetic
Particle, Composition and Thermal Plasma Suite (ECT),
which operates one of the instrument sets. “We think we’re finally going
to be able to answer some basic questions about the physics of the Van Allen
Belts, questions that have been around for over 50 years.”
Chan says it is particularly satisfying that Rice is part of
a project that promises to solve long-standing mysteries of the Van Allen Belts—and
not only because Rice emeritus professor John Freeman was a student of James
Van Allen himself. “There’s a very strong theory and simulation group at Rice in
space plasma physics,” he says. “The most famous
space physics model developed here, the Rice Convection Model, operates in a
similar region of space to the Van Allan Belts, but with generally lower-energy
particles.”
Chan says the outer radiation belts contain energy in the
million-electron-volt range. “We’re especially interested in the electrons,
which in those energies are relativistic. They travel close to the speed of
light and are much more energetic than anything else out there,” he says.
His task will be to use data gathered from the probes to
verify and refine his group’s theories and simulations. “We want to understand
the dynamic variability of the outer belt and eventually be able to predict it
to the point where it could be useful for spacecraft operators and designers,”
he says. “That is one of the practical consequences of this research.”
High-energy particles come primarily from the sun, which
bombards Earth through coronal mass ejections (CME) that are expected to become
more frequent as the sun approaches its “solar max” in 2013, and from coronal
holes that appear during less-active periods.
“Most of what we call magnetic storms are driven by
solar-wind events,” Chan says. “Some are CMEs, which tend to produce the most
violent storms. But another type is caused by high-speed streams in the solar
wind that originate in coronal holes. In certain wavelengths, we see dark
patches, usually near the poles. But they sometimes creep down, especially
approaching solar minimum.
“These holes have low density but very fast streaming solar
wind,” he says, “and can cause some of the largest increases in relativistic
electrons.” The particles can overwhelm sensitive electronic instruments like
those aboard the location-finding GPS satellites that dot the skies and
frequently spend time in the harsh environment of the Van Allen Belts.
“Usually spacecraft avoid these regions, or they switch off
equipment when they pass through because it disrupts their operation,” Chan
says. “Radiation degrades the instruments’ lifetimes, but the RBSP satellites
are designed to fly through these regions and last a number of years.”
The twin satellites will allow researchers to gather the
most accurate data yet from energetic events in the Van Allen Belts. They will
sweep within 400 miles of Earth and out through the belts, which range from
about 8,000 to 40,000 miles. Because researchers can see events triggered by
solar activity coming (particularly with the STEREO and Hinode satellites
standing guard), they’ll know where and when to look.
Chan says he hopes the probes’ sophisticated instruments
will lead to some surprises. “Because electrons are all identical, it’s hard to
know where they’re coming from. Nevertheless, we think the majority of them are
coming from the sun,” he says.
“There was an interesting theory a while back that some of
these relativistic electrons were coming from Jupiter,” Chan says. “There are
times—and it’s not as crazy as it sounds—when Jupiter is magnetically connected
to Earth. We’re on the same interplanetary magnetic field lines, and Jupiter is
a strong source; it makes lots of radio waves and energetic electrons.
“We see some small peaks about when we expect to see Earth
and Jupiter magnetically connected. It’s a great idea and interesting to think
about, but it’s probably very weak,” he says. “If it turns out to be much
stronger than expected, it would be really interesting.
“The most interesting results scientists get are the ones we
don’t expect,” Chan says. “We design the missions looking for certain things
and try to allow enough data collection in regions that haven’t been explored
enough to look for something new. And you always hope you’ll find something
new.”
Source: Rice University
