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

Dark Lightning: Terrestrial Gamma Ray Flashes irradiate passengers

"What are the radiation doses to airplane passengers from the intense bursts of gamma-rays that originate from thunderclouds?" Florida Institute of Technology Department of Physics and Space Science faculty members addressed the issue and presented their terrestrial gamma ray flashes (TGFs) research modeling work at a press conference meeting of the European Geosciences Union in Vienna, Austria, April 10, 2013.

Joseph Dwyer

Joseph Dwyer, Ningyu Liu and Hamid Rassoul discussed a new physics-based model of radiation dose calculations and compared the calculations to previous work.

Scientists have known for almost a decade that thunderstorms are capable of generating brief but powerful bursts of gamma-rays called terrestrial gamma-ray flashes (TGFs).

These flashes of gamma-rays are so bright they can blind instruments many hundreds of kilometers away in outer space.

Because they can originate near the same altitudes at which commercial aircraft routinely fly, scientists have been trying to determine whether or not terrestrial gamma ray flashes present a radiation hazard to individuals in aircraft.

Until recently, the work to answer that question was hampered by a poor understanding of exactly how these gamma-rays are generated by thunderstorms, with initial dose estimates ranging from not-so-safe to downright scary.

Ningyu Liu

Now, scientists at Florida Tech have developed a promising physics-based model of exactly how thunderstorms manage to produce high-energy radiation.

According to their model, instead of creating normal lightning, thunderstorms can sometimes produce an exotic kind of electrical breakdown that involves high-energy electrons and their anti-matter equivalent called positrons.

The interplay between the electrons and positrons causes an explosive growth in the number of these high-energy particles, emitting the observed terrestrial gamma ray flashes while rapidly discharging the thundercloud, sometimes even faster than normal lightning.

Even though copious gamma-rays are emitted by this process, very little visible light is produced, creating a kind of electrical breakdown within the storms called "dark lightning."

Recent modeling work of dark lightning shows that it can explain many of the observed properties of terrestrial gamma ray flashes.

The model also calculates the radiation doses received by individuals inside aircraft that happen to be in exactly the wrong place at the wrong time.

Hamid Rassoul

Near the tops of the storms, for the types of terrestrial gamma-ray flashes that can be seen from space, the radiation doses are equivalent to about 10 chest x-rays, or about the same radiation people would receive from natural background sources over the course of a year.

"However, near the middle of the storms, the radiation dose could be about 10 times larger, comparable to some of the largest doses received during medical procedures and roughly equal to a full-body CT scan," said Dwyer.

"Although airline pilots already do their best to avoid thunderstorms, occasionally aircraft do end up inside electrified storms, exposing passengers to terrestrial gamma ray flashes."

"On rare occasions, according to the model calculation, it may be possible that hundreds of people, without knowing it, may be simultaneously receiving a sizable dose of radiation from dark lightning."

It is not known yet how often, if ever, this actually occurs, but ongoing research is working to address this issue.