Astronomers Solve Puzzle of Mysterious Streaks In Radio Images of the Sky

KentuckyFC (1144503) writes 'Back in 2012, astronomers constructed an array of 256 radio antennas in the high deserts of New Mexico designed to listen for radio waves produced by gamma ray bursts, one of the most energetic phenomena in universe and thought to be associated with the collapse of a rapidly rotating stars to form neutron stars and black holes. The array generates all sky images of signals produced in the 25 MHz to 75 MHz region of the spectrum. But when researchers switched it on, they began to observe puzzling streaks across the sky that couldn't possibly be generated by gamma ray bursts. One source left a trail covering more than 90 degrees of the sky in less than 10 seconds. This trail then slowly receded to an endpoint which glowed for around 90 seconds. Now the first study of these transient radio signals has discovered that they are almost certainly produced by fireballs as they burn up after entering the Earth's atmosphere. The conclusion comes after the researchers were able to match several of the radio images with visible light images of fireballs gathered by NASA's All Sky Fireball Network. That solves the mystery but not without introducing another to keep astrophysicists busy in future. The question they're scratching their heads over now is how the plasma trails left by meteors can emit radio waves at this frequency.'

Meteor burst communications

[Anonymous Coward]

http://en.wikipedia.org/wiki/Meteor_burst_communications

Re:Cyclotron Radiation?

[Anonymous Coward]

What about cyclotron radiation from the ions in the meteor plasma trails? Could charge carriers be orbiting in the plasma trail under the influence of the Earth's magnetic field, and radiating RF in the megahertz band?

in a word: maybe

From the paper: "If a magnetic eld of 10 to 15 G were present within the trail, it follows that cyclotron radiation would be emitted at the observed frequencies by the electrons in the plasma. However, the surface geomagnetic eld is only 0.5 G, so this would require the generation of a strong magnetic eld by a reball, an eect that has never been observed."

Reflected EM Waves?

[Anonymous Coward]

Chances are, the detected frequencies may be due to reflection of radio energy that's been transmitted by transmitters around the world. Radio amateurs have been using meteor-scatter as a way of reflecting radio frequency energy for short periods to make intercontinental contact - so this may be a contributor to the signals detected at "radio quiet" locations.

Re:Is this not the same as grass noise?

[Peter H.S.]

I've heard reports of people laying on the ground and "hearing" meteors. What baffled scientist about this was people were hearing them realtime and not delayed due to the speed of sound. They finally realized that it was radio waves emitted by the meteors causing the grass to vibrate and they were hearing the vibrations.

Maybe I dreamed it...

I have heard meteors making real time sounds as they streaked across the sky. It was during the 2001 Leonids meteor storm. It was in a city with not a blade of grass in sight. This particular meteor storm was widely reported as emitting crackling and hissing sounds:
http://www.spaceweather.com/me... [spaceweather.com]

There has been some speculation about what could cause such sounds. Some have suggested that “electrophonic meteors” can cause secondary lower frequency vibrations to be heard simultaneously, but it is just a suggestion since good quality data is missing.

The RTFA discovery is just a part of a new series of discoveries that shows we know a lot less about meteors and comets than we thought we did.

Re:Meteor burst communications

[teridon]

Yes, people use ionization trails to reflect their radio transmissions, but in TFA they discount this as the source of the emissions:

Meteor trails are known to reflect radio waves and indeed this has been one way of spotting them in the past.

But Obenberger and co reject this idea for a number of reasons. First, human radio transmissions are usually polarised and so any reflections ought to be polarised as well. The team found no evidence of this.

At the same time, human radio transmissions have easily identifiable spectra but the team found no evidence of this either in the data from the Long Wavelength Array.

"It is therefore our conclusion that ïreball trails radiate at low frequencies," they say.

Re:Is this not the same as grass noise?

[Tapewolf]

That was sufficiently weird that I had to look it up: http://www.livescience.com/386... [livescience.com]