NASA leads NSF firefly mission to study lightning - Video

Somewhere across the Earth each day and night, there's a lightning flash. The globe experiences lightning some 50 times a second, yet the details of what initiates this common occurrence and what effects it has on the atmosphere – lightning may be linked to incredibly powerful and energetic bursts called terrestrial gamma ray flashes, or TGFs—remains a mystery.

Firefly, a milk-carton-sized satellite, will study gamma-ray bursts that accompany lightning.

Credit: Zina Deretsky, National Science Foundation

In mid-November, a football-sized mission called Firefly, which is funded by the National Science Foundation, will launch into space to study lightning and these gamma ray flashes from above.

The Firefly instrument is what's known as a cubesat, a very small satellite that offers the chance for quality space science with a relatively inexpensive price tag.

"We can do great science with these small missions," said Doug Rowland, the principal investigator for Firefly at NASA's Goddard Space Flight Center in Greenbelt, Md.

"Firefly will gather up to a year of observations on the mysterious workings of lightning. Lightning is so familiar we tend to take it for granted, but we really don't know the details of how it works—even though it is a critical part of the global electric circuit, and has obvious social and technological effects."

Lightning is ubiquitous and intimately connected to life on Earth, but we don't often think about what's happening higher up in the atmosphere.

The radiation generated by lightning is so intense that it can generate antimatter and gamma rays within TGFs just a few miles of the ground.

NASA's Compton Gamma Ray Observatory first discovered TGFs in the 1990s. Designed to look outward at cosmic sources of gamma rays, the mission also caught rare but tantalizing glimpses of gamma rays coming from Earth.

This is an artist's rendition of the football-sized Firefly satellite in low-Earth orbit. 

Firefly's mission is to study the relationship between lightning and huge bursts of gamma rays called terrestrial gamma ray flashes. 

Credit: NASA/Goddard Space Flight Center

Terrestrial Gamma-Ray Flashes (TGF) Additional Hazards To Air Crew and Travellers

A representative sketch of electric and magnetic fields in a thunderstorm and some of the phenomena they produce.

Terrestrial Gamma-ray flashes (TGFs) may be just one aspect of thunderstorm activity in addition to elves, sprites, blue jets and ordinary lightning. Credit: Stanford University.

Instruments scanning outer space for cataclysmic explosions called gamma-ray bursts are detecting intense flashes of gamma-ray energy right here in the friendly skies of Earth.

These terrestrial gamma-ray flashes, or TGFs, blast through thunderstorms close to the altitude where commercial airliners fly. In fact, they could be too close for comfort.

In a recent study, scientists estimated that airline passengers could be exposed to 400 chest X-rays worth of radiation by being near the origin of a single millisecond blast.

Joe Dwyer of the Florida Institute of Technology took part in that research, which used observations from NASA's Reuven Ramaty High Energy Solar Spectroscopic Imager, or RHESSI, to estimate the danger TGFs pose.

"We believe the risk of encountering a TGF in an airplane is very small," says Dwyer. "I wouldn't hesitate to take a flight. Pilots already avoid thunderstorms because of turbulence, hail, and lightning, and we may just have to add TGFs to the list of reasons to steer clear of those storms."

But, he stresses, "it's worth looking into."

NASA's Gamma-ray Burst Monitor (GBM) on the Fermi Gamma-ray Telescope will help evaluate the hazards.

"GBM provides the best TGF data we have so far," says Dwyer. "It gets better measurements of their spectra than any previous instrument, giving us a more accurate idea of just how energetic they are."

Although TGFs are quite brief (1-2 milliseconds), they appear to be the most energetic events on Earth. They belch destructive gamma-rays packing over ten million times the energy of visible light photons - enough punch to penetrate several inches of lead.

"It's amazing," says Jerry Fishman, a co-investigator for the Gamma-ray Burst Monitor. "They come blasting right through the whole Fermi spacecraft and light up all of our detectors. Very few cosmic gamma-ray bursts manage to do this!"

The origin of TGFs is still a mystery, but researchers know this much: TGFs are associated with thunderstorms and lightning. "We think the electric field in a thunderstorm may get so strong that the storm itself turns into a gamma-ray factory," says Dwyer. "But we don't know exactly how or why or where inside the storm this happens."

So no one yet knows how often, if ever, planes end up in the wrong place at the wrong time.

It's possible that lightning bolts trigger TGFs. Or maybe TGFs trigger lightning bolts. Researchers aren't sure which comes first. GBM's excellent timing accuracy - to within 2 microseconds - will help solve this riddle.

"For some of the TGFs, we've pinpointed the associated lightning," says Dwyer. "This information along with the spectrum should help us figure out how deep in the atmosphere a TGF source is and how many gamma-rays it's emitting. Then we can determine the altitude and location they're coming from in the thunderstorm."