April 20, 2009 -- From his place in New Mexico, Thomas Ashcraft recently took in a live show -- even though it unfolded some 390 million-plus miles away on Jupiter. All he needed was a few antennas, some short wave radios and a recorder to document the event.
Listen to a recording of Jupiter's sounds here, courtesy of Thomas Ashcraft.
It turns out Earth's big brother can belt out a tune ... well a few notes anyway. The radio waves come to Earth in two varieties: long bursts and short ones. They appear when particular parts of Jupiter are aligned with Io -- its closest and most volcanically active moon -- and receiving stations on Earth.
The stations can be very simple. Ashcraft, a 58-year-old artist who has been listening to the sounds Jupiter, the sun and other celestial bodies for about 20 years, uses a directional antenna system known as a Yagi antenna, a series of secondary dipole antennas and a short wave radio.
There's a group called Radio Jove that sells kits for under $20. If owning the goods isn't your thing, the University of Florida Radio Observatory streams its catch live on the Internet.
The short bursts last just a few milliseconds before shutting down and shifting over to other radio frequencies, Francisco Reyes, director of the UF radio observatory, told Discovery News.
"It's like pebbles or hail falling on a tin roof," Reyes said.
The long notes can linger for 30 minutes, or even an hour or two.
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"They change in intensity, but that's not intrinsic to Jupiter," Reyes said. "It's caused by the interplanetary medium and (Earth's) scintillating ionosphere. It sounds like waves crashing on a beach."
How it's all happening is somewhat of a mystery. Scientists believe it begins with fast-moving streams of magnetized plasma being pulled down over the Jupiter's poles and emitting radio waves in the process, a phenomenon known as cyclotron maser mechanism.
The volcanic moon Io seems to play a key role, by hurling electrically conductive gases into Jupiter's magnetosphere. Io's gases collect in a doughnut-shaped region and as the moon Io zips around Jupiter, it plows through this structure, creating waves like the wake of a boat. Scientists think the waves, coupled with magnetic forces, provide power to Jupiter's polar regions, sparking the radio storms.
Timing is everything when it comes to tuning in to Jupiter radio. The emissions are not dispersed in all directions, but flow in the shape of hollow cone. Earth has to be precisely positioned in the narrow edge of the cone to receive the radio signals.
"The sources are close to Jupiter's northern hemisphere in very high latitude," Reyes said. "Exactly where, we don't know. That's what we're trying to determine."
Jupiter also is a bit fickle about its broadcasts.
"There's no guarantee that there will be a radio burst," Ashcraft said, adding that there are about 20 optimal alignments of Jupiter, Io and Earth every year.
There also are a lot of emissions that can masquerade as Jupiter waves, including lightning storms on Earth and all sorts of noises tied to human activities, such as computer monitors and even coffee grinders.
"The man-made interference is a problem in radio astronomy," Ashcraft said. "It's becoming harder and harder to weed out the spurious signals."
Turns out, Jupiter had a double-header this weekend, with radio bursts on both Friday and Saturday.
"The past three years, Jupiter has been in less than optimal alignment for receiving radio storms due to orbital tilt," Ashcraft wrote in an email. "This year is a much better alignment with Earth.
"The strength of the two radio storms was impressive," he added. "This bodes well for future Jovian radio storms this year."
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