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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.
The ‘Firefly’ CubeSat will fly through thunderstorms and lightning. Credit: NASA |
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.
Source: National Science Foundation
