An illustration shows antimatter shooting above a thunderstorm.
An illustration shows high-energy electrons and positrons from Earth traveling into space. {Illustration J. Dwyer/FIT, NASA}

Thunderstorms Shoot Antimatter Beams Into Space
by Richard A. Lovett / January 11, 2011

Thunderstorms can shoot beams of antimatter into space—and the beams are so intense they can be spotted by spacecraft thousands of miles away, scientists have announced. Most so-called normal matter is made of subatomic particles such as electrons and protons. Antimatter, on the other hand, is made of particles that have the same masses and spins as their counterparts but with opposite charges and magnetic properties. Recently, radiation detectors on NASA’s Fermi Gamma-ray Space Telescope lighted up for about 30 milliseconds with the distinctive signature of positrons, the antimatter counterparts of electrons.

Scientists were able to trace the concentrated burst of radiation to a lightning flash over Namibia, at least 3,000 miles (5,000 kilometers) away from the Earth-orbiting telescope, which was passing above Egypt at the time. “This is a fundamental new discovery about how our planet works,” said Steven Cummer, a lightning researcher from Duke University who was not part of the study team. “The idea that any planet has thunderstorms that can create antimatter and launch it into space is something out of science fiction. The fact that our own planet is doing it is truly amazing.”

Scientists already knew that thunderstorms can emit gamma rays—the most energetic form of light—and that gamma rays in turn can create positrons through a process called pair formation. When a gamma ray with the right amount of energy interacts with an air atom, energy from the gamma ray is converted into matter, one electron and one positron, lightning expert Joseph Dwyer said yesterday during a meeting of theAmerican Astronomical Society in Seattle, Washington. Scientists wouldn’t have been surprised to see a few positrons accompanying any intense gamma ray burst, added Dwyer, of the Florida Institute of Technology in Melbourne. But the lightning flash detected by Fermi appeared to have produced about 100 trillion positrons: “That’s a lot,” he said.

What seems to have happened is that positrons created by the lightning were herded into a tight beam by Earth’s magnetic field, said study leader Michael Briggs of the University of Alabama, Huntsville. The beam funneled positrons from the Namibian storm to the Fermi spacecraft. A few milliseconds after hitting the spacecraft, the beam struck a more northerly section of Earth’s magnetic field, Briggs added. This caused some of the positrons to bounce back the way they had come, hitting the spacecraft with a second beam, like an echo.

Earth is constantly being bombarded by radiation from the sun, as well as cosmic rays from distant but violent events, such as powerful supernovae. Considering the amount of positrons in the beam Fermi detected, the thunderstorm was briefly creating more radiation—in the form of positrons and gamma rays—than what hits Earth’s atmosphere from all other cosmic sources combined, Dwyer noted. The researcher has previously said, however, that the danger of thunderstorm radiation to airline travelers is extremely low. Duke’s Cummer added that nobody knows why some thunderstorms produce gamma rays while most do not. “We really don’t understand a lot of the details about how lighting works,” he said. But discovering the creation of positrons “gives us a very, very important clue as to what’s happening.”

{A paper about the discovery of antimatter in thunderstorms has been accepted for publication in the journal Geophysical Research Letters.}


Antimatter seems impossibly exotic, something that exists only in particle accelerators or in cosmic events many light-years away. But the next time there’s a big thunderstorm, look up at the sky: you’re looking at the creation of natural antimatter bursts. NASA’s Fermi Gamma-ray Space Telescope picked up on the antimatter by monitoring several recent thunderstorms. Lightning is known to produce what’s known as a terrestrial gamma-ray flash, or TGF, which is basically a brief burst of gamma-rays. There are a few different ways to create gamma-rays, including the collision of an electron and its antimatter counterpart, the positron. When these two particles annihilate each other, they create gamma-rays with energies of precisely 511,000 electron volts. Fermi can pick up on the specific energies of the gamma-rays, and it was able to find at least four of the 130 observed TGFs with that particular energy signature. This isn’t a common phenomenon, then, but neither is it particularly rare, considering Fermi has only been watching the storms for about a year.

So how is the antimatter created in the first place? Thunderstorms possess electric fields at the tops of their systems, and particularly powerful storms are able to funnel huge swaths of electrons upwards at great speed. These electrons run into molecules, which alter their course and cause the electrons to emit gamma-rays. Some of these gamma-rays, traveling at near the speed of light, then pass near an atomic nucleus, which cause the ray to turn into an electron and positron. The matter and antimatter pair then travel out into space along Earth’s magnetic field. The entire process only takes a couple of milliseconds. Amazingly, we’ve only known that thunderstorms can create gamma-rays (not to mention x-rays) for about a year, so the realization that they can create antimatter as well would have been unimaginable as recently as 2009. Duke researcher Steven Cummer puts it simply: “I think this is one of the most exciting discoveries in geoscience in a very long time. [It] seems like something straight out of science fiction.”

Illustration: NASA’s Goddard Space Flight Center / J. Dwyer, Florida Inst. of Technology

ASA’s Fermi Catches Thunderstorms Hurling Antimatter into Space /  01.10.11

Scientists using NASA’s Fermi Gamma-ray Space Telescope have detected beams of antimatter produced above thunderstorms on Earth, a phenomenon never seen before. Scientists think the antimatter particles were formed in a terrestrial gamma-ray flash (TGF), a brief burst produced inside thunderstorms and shown to be associated with lightning. It is estimated that about 500 TGFs occur daily worldwide, but most go undetected. “These signals are the first direct evidence that thunderstorms make antimatter particle beams,” said Michael Briggs, a member of Fermi’s Gamma-ray Burst Monitor (GBM) team at the University of Alabama in Huntsville (UAH). He presented the findings Monday, during a news briefing at the American Astronomical Society meeting in Seattle.

Fermi is designed to monitor gamma rays, the highest energy form of light. When antimatter striking Fermi collides with a particle of normal matter, both particles immediately are annihilated and transformed into gamma rays. The GBM has detected gamma rays with energies of 511,000 electron volts, a signal indicating an electron has met its antimatter counterpart, a positron. Although Fermi’s GBM is designed to observe high-energy events in the universe, it’s also providing valuable insights into this strange phenomenon. The GBM constantly monitors the entire celestial sky above and the Earth below. The GBM team has identified 130 TGFs since Fermi’s launch in 2008. “In orbit for less than three years, the Fermi mission has proven to be an amazing tool to probe the universe. Now we learn that it can discover mysteries much, much closer to home,” said Ilana Harrus, Fermi program scientist at NASA Headquarters in Washington.

On Dec. 14, 2009, while NASA’s Fermi flew over Egypt, the spacecraft intercepted a particle beam from a terrestrial gamma-ray flash (TGF) that occurred over its horizon. Fermi’s Gamma-ray Burst Monitor detected the signal of positrons annihilating on the spacecraft — not once, but twice. After passing Fermi, some of the particles reflected off of a magnetic “mirror” point and returned.

The spacecraft was located immediately above a thunderstorm for most of the observed TGFs, but in four cases, storms were far from Fermi. In addition, lightning-generated radio signals detected by a global monitoring network indicated the only lightning at the time was hundreds or more miles away. During one TGF, which occurred on Dec. 14, 2009, Fermi was located over Egypt. But the active storm was in Zambia, some 2,800 miles to the south. The distant storm was below Fermi’s horizon, so any gamma rays it produced could not have been detected. “Even though Fermi couldn’t see the storm, the spacecraft nevertheless was magnetically connected to it,” said Joseph Dwyer at the Florida Institute of Technology in Melbourne, Fla. “The TGF produced high-speed electrons and positrons, which then rode up Earth’s magnetic field to strike the spacecraft.”

The beam continued past Fermi, reached a location, known as a mirror point, where its motion was reversed, and then hit the spacecraft a second time just 23 milliseconds later. Each time, positrons in the beam collided with electrons in the spacecraft. The particles annihilated each other, emitting gamma rays detected by Fermi’s GBM.

graphic depicting how Fermi detected a terrestrial gamma-ray flash

Scientists long have suspected TGFs arise from the strong electric fields near the tops of thunderstorms. Under the right conditions, they say, the field becomes strong enough that it drives an upward avalanche of electrons. Reaching speeds nearly as fast as light, the high-energy electrons give off gamma rays when they’re deflected by air molecules. Normally, these gamma rays are detected as a TGF. But the cascading electrons produce so many gamma rays that they blast electrons and positrons clear out of the atmosphere. This happens when the gamma-ray energy transforms into a pair of particles: an electron and a positron. It’s these particles that reach Fermi’s orbit. The detection of positrons shows many high-energy particles are being ejected from the atmosphere. In fact, scientists now think that all TGFs emit electron/positron beams. A paper on the findings has been accepted for publication in Geophysical Research Letters.

“The Fermi results put us a step closer to understanding how TGFs work,” said Steven Cummer at Duke University. “We still have to figure out what is special about these storms and the precise role lightning plays in the process.” NASA’s Fermi Gamma-ray Space Telescope is an astrophysics and particle physics partnership. It is managed by NASA’s Goddard Space Flight Center in Greenbelt, Md. It was developed in collaboration with the U.S. Department of Energy, with important contributions from academic institutions and partners in France, Germany, Italy, Japan, Sweden and the United States. The GBM Instrument Operations Center is located at the National Space Science Technology Center in Huntsville, Ala. The team includes a collaboration of scientists from UAH, NASA’s Marshall Space Flight Center in Huntsville, the Max Planck Institute for Extraterrestrial Physics in Germany and other institutions.

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