'CubeSat'
will help solve mysteries of terrestrial gamma ray flashes, 1,000 times more
powerful than 'northern lights'
Imagine a fully-instrumented satellite
the size of a half-gallon milk carton.
Then imagine that milk carton whirling
in space, catching never-before-seen glimpses of processes thought to be linked
to lightning.
The little satellite that could is a
CubeSat called Firefly, and it's on a countdown to launch next year.
CubeSats, named for the roughly
four-inch-cubed dimensions of their basic building elements, are stacked with
modern, smartphone-like electronics and tiny scientific instruments.
Built mainly by students and hitching
rides into orbit on NASA and U.S. Department of Defense launch vehicles, the
small, low-cost satellites recently have been making history. Many herald their
successes as a space revolution.
Several CubeSat projects funded by the
National Science Foundation (NSF) are currently in orbit, making
first-of-their-kind experiments in space and providing new measurements that
help researchers understand Earth's upper atmosphere.
Firefly is designed to help solve the
mystery of a phenomenon that's linked with lightning: terrestrial gamma rays,
or TGFs.
Bursts of gamma rays usually occur far
out in space, near black holes and other high-energy cosmic phenomena. Scientists were surprised when, in the
mid-1990s, they found powerful gamma-ray flashes happening in the skies over
Earth.
Powerful natural particle accelerators
in the atmosphere are behind the processes that create lightning. TGFs result
from this particle acceleration.
Individual particles in a TGF contain a
huge amount of energy, sometimes more than 20 mega-electron volts. The aurora
borealis, for example, is powered by particles with less than one-thousandth as
much energy as a TGF.
But what causes a TGF's high-energy
flashes? Does it trigger lightning--or does lightning trigger it? Could it be
responsible for some of the high-energy particles in the Van Allen radiation
belts, which can damage satellites?
Firefly soon will be on the job, finding
out.
The CubeSat will look specifically for
gamma-ray flashes coming from the atmosphere, not space, conducting the first
focused study of TGF activity.
The Firefly team is made up of
scientists and students at Siena College in Loudonville, N.Y.; NASA Goddard
Space Flight Center in Greenbelt, Md.; the Universities Space Research
Association in Columbia, Md.; the Hawk Institute for Space Science, Pocomoke
City, Md.; and the University of Maryland Eastern Shore, Princess Anne, Md.
Students are involved in all aspects of
the mission, from design and development, through fabrication and testing, to
operations and data analysis.
Firefly will carry a gamma-ray detector
along with a suite of instruments to detect lightning, says Therese Moretto
Jorgensen, program director in NSF's Division of Atmospheric and Geospace
Sciences, which funds Firefly and its CubeSat companions in space.
The CubeSat will return the first
simultaneous measurements of TGFs and lightning.
When thunderstorms happen, powerful
electric fields stretch upward for miles, into the upper atmosphere. These electric
fields accelerate free electrons, whirling them to speeds that are close to the
speed of light.
When these ultra-high-speed electrons
collide with molecules in the air, they release high-energy gamma rays as well
as more electrons, starting a cascade of electrons and TGFs.
"Gamma rays are thought to be
emitted by electrons traveling at or near the speed of light when they're
slowed down by interactions with atoms in the upper atmosphere," says
Moretto Jorgensen. "TGFs are among our atmosphere's most interesting
phenomena."
Atmospheric scientists think TGFs occur
more often than anyone realized and are linked with the 60 lightning flashes
per second that happen worldwide, says scientist Allan Weatherwax of Siena
College, a lead scientist, along with Doug Rowland of NASA's Goddard Space
Flight Center, on the Firefly project.
Build-up of electric charges at the tops
of thunderclouds from lightning discharges can create a large electric field
between clouds and the ionosphere, the outer layer of Earth's atmosphere. But
how this might lead to TGFs is unknown.
"Firefly will provide the first
direct evidence for a relationship between lightning and TGFs," says
Weatherwax. "Identifying the source of terrestrial gamma-ray flashes will
be a huge step toward understanding the physics of lightning and its effect on
Earth's atmosphere."
Unlike lightning, a TGF's energy is
released as invisible gamma rays, not visible light. TGFs therefore don't
produce colorful bursts of light like many lightning-related phenomena. But
these unseen eruptions could help explain why brilliant lightning strikes
happen.
Following Firefly is FireStation, a set
of miniaturized detectors for optical, radio and other lightning measurements.
FireStation will fly a bit higher than
Firefly.
Its orbit is on the International Space
Station.
-- Cheryl Dybas, NSF (703) 292-7734
cdybas@nsf.gov
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