When University of New Mexico Physics & Astronomy Professor Greg Taylor turned on the first Long Wavelength Array (LWA1) station in 2011, he wasn’t exactly sure what they were going to find. Fast forward five years, and now, Taylor and recent Ph.D. graduate Ken Obenberger have detected and studied a strange, meteoric phenomenon no one else had ever seen.
The pair had discovered a new type of emission coming from fireballs streaking across earth’s upper atmosphere.
“When we talk about fireballs, we’re talking about large meteors that enter the earth’s atmosphere and explode,” said Taylor.
Using LWA1, a low-frequency radio telescope station made up of 256 dual-polarization dipoles, the team has tracked about 150 of these fireballs flying more than 90 kilometers (about 56 miles) above us in the sky.
What sets their discovery apart is the strange reaction taking place that allows their radio telescope to detect these meteors. Typically, when a space rock enters earth’s atmosphere it explodes and can be seen optically for only a few seconds. According to Taylor’s data, these fireballs can radiate radio waves for up to several minutes.
“The meteor burns up and produces this big trail of plasma and then somehow that’s producing radio emission,” said Obenberger, who graduated with his Ph.D. in May. “But, we still don’t really understand what’s causing that emission.”
Because this project is studying a previously undiscovered type of meteor emission, the research naturally produces a lot of questions for Taylor and Obenberger. And while they still have a lot to learn, they have been able to answer some questions.
Taylor said one of the more interesting results they’ve found is the altitude dependence of these fireballs. For the radio emission to occur, the meteor must be above the 90 kilometer threshold; any lower and the it acts like a traditional meteor. Obenberger believes this has something to do with atmospheric density.
“At the higher altitudes, the atmosphere is less dense which means there are less air molecules for electrons to run in to,” he said. “So, the idea is that the electrons are radiating and in order to radiate they need to shake and move around. But, when the atmosphere is thick they’ll run in to those molecules more frequently and lose their energy. At higher altitudes the air is thinner and electrons are free to radiate for a longer period of time.”
Because of that interaction, the project is also giving researchers the ability to learn more about the upper atmosphere, a region that has been difficult to study in the past. In the future, the team hopes to learn more about that interaction and discover where all the energy in these fireballs is coming from. Taylor believes the research may also be able to answer some much bigger questions.
“If we can learn something about meteors we can learn something about the solar system,” he said. “I really believe that we could learn something about the origin of our solar system from this research.”
Taylor and his team recently finished construction on a second telescope station, at Sevilleta National Wildlife Refuge, that will help increase the resolution and fidelity of the radio imaging. Taylor hopes to continue to secure funding to be able to build even more stations in the future.
So far, Obenberger has been the first author on four publications stemming from this research, with two more papers in the works. Now working on his post-doc at the Air Force Research Lab in Albuquerque, Obenberger said this project was a dream come true for a young researcher.
“We have millions of images, 20,000 hours of data and, for a time, I was the only person looking at it,” he said. “It’s sort of a graduate student’s dream.”