|
 May 22, 2000 -- As
the planet Jupiter passes behind the Sun this month, it's temporarily lost
from view to astronomers. "Out-of-sight" doesn't necessarily mean
"out-of-mind," though, when it comes to the biggest planet in the solar
system. Even now, scientists from NASA's Goddard Space Flight Center and
the University of Florida are busily working on Radio JOVE,
an initiative that could inspire thousands of students to look at and
listen to Jupiter when it eventually emerges from the Sun's
glare.
"Jupiter is a powerful source of radio waves that we can
pick up here on Earth using simple antennas and shortwave receivers," says
Dr. Jim Thieman, an astrophysicist at the NASA Goddard Space Flight Center
who's leading the Radio JOVE effort. "Human ears can't hear these
radio waves directly, but when they're converted to audio signals by a
receiver, they sound really wonderful."
Above: It may look like a
clothesline, but it's really a radio telescope. This simple Radio
JOVE wire antenna tuned for 20.1 MHz is capable of detecting powerful
radio bursts from the planet Jupiter.
Thanks
to Radio JOVE, the pleasure of listening to Jupiter's
exotic sounds is no longer exclusive to professional astronomers.
Amateur astronomers, ham radio enthusiasts, middle- to high-school and
college students can tune in, too.
"We've come up with a
radio-telescope kit that most high school science classes can put
together," explains Thieman. "The kits include all of the parts required
to construct a 20 MHz receiver, along with transmission cables and wire
for the antennas. The antennas are dual half-wave dipoles, each about 20
feet long and mounted 20 feet apart. The kit doesn't include the PVC
structures we recommend for mounting the wires, but those are inexpensive
and easy to get at a local hardware store. You can also use wood for
mounting."
You might imagine that a radio telescope capable of
detecting a planet hundreds of millions of kilometers away would be
expensive, but these kits sell at cost for just $115.
"So
far we've sold 192" says Bill Pine, a California high school teacher who's
distributing the Radio JOVE kits through The INSPIRE Project, Inc.,
a non-profit educational corporation. "Most have been to schools -- I
would estimate around 140. The rest have been purchased by radio amateurs
and other interested individuals."
Radio JOVE participants
can build their own radio telescopes, make observations, and help
scientists monitor activity in Jupiter's enormous magnetosphere. It's the
whole scientific process in one project, says Thieman. For students who
can't build their own radio telescope, there will be an online observatory
where kids can monitor Jupiter on the World Wide Web.
For more information about how to
join, visit the Radio
JOVE home page at the NASA Goddard Space Flight Center.
WJUP -- The Red Spot on Your
Dial
Shortwave radio signals from Jupiter aren't a sign
of extraterrestrial intelligence -- the emissions are generated naturally
by plasma instabilities in Jupiter's magnetosphere. Space physicists are
still debating the details, but most experts agree that ionized gas in the
uppermost atmosphere near Jupiter's magnetic poles sometimes behaves like
a powerful radio laser (or "maser"). The radiation can be so intense that
Jupiter frequently outshines the Sun as a radio source at ham radio
wavelengths.
Where does the radio laser mechanism get so much power? It's a
circuitous story that starts on Jupiter's volcanic moon Io.
|
Above: A ground-based telescopic image of
the Io torus, showing emissions from singly ionized sulfur. Jupiter
is at the center and the Io torus is the faint ring extending to the
orbit of Io at 5.9 Jupiter radii. [more information
from the American Geophysical
Union] | Tidal forces from Jupiter and
the other large Galilean
satellites superheat the interior of Io and make it the most volcanic
body in the solar system. Volcanic ejecta are thrown far above Io's
surface; much of it enters orbit around Jupiter, forming a huge gaseous
donut around the giant planet. With a diameter the size of Io's orbit, the
electrically conducting "Io torus" spans 844 thousand kilometers and has
an important impact on Jupiter's magnetic environment. As Io's orbital
motion carries it through this magnetized ring of ionized gas, a huge
electrical current flows between Io and Jupiter. Carrying about 2 trillion
watts of power, it's the biggest DC electrical circuit in the solar
system.
[Editor's note: this description is
simplified for clarity. Unlike a DC circuit that you might construct using
batteries and wires for a science fair project, plasma physicists believe
that current in the Io-Jupiter system is carried by a type of magnetic
plasma wave called Alfven
waves. The details are the subject of ongoing
research.]
This awesome current is the power source for
plasma waves that give rise to the laser-like radio emissions. The radio
signals travel away from Jupiter's magnetic poles in cone-shaped beams
that rotate with the giant planet every 9 hours and 55 minutes. In this
respect Jupiter is like a
slow-turning pulsar. When the beams sweep past our planet, listeners
can pick up Jovian radio bursts in the shortwave bands between 15 and 40
MHz.
Above:
This frame from a
computer animation shows the cone-shaped radio emission beam near
Jupiter's north magnetic pole. (Not shown is another conical beam near the
south magnetic pole.) The radio beams are hollow cones, meaning that
Earth-bound observers can pick up signals only when the thin edge of the
cone sweeps past our planet. The loop labeled IFT is the "Io Flux Tube," a
bundle of magnetic field lines that pass through Io and connect to
Jupiter's polar auroral zone. The powerful electrical current that powers
the radio laser flows along magnetic field lines in and near the IFT. For
a better view of Jupiter and its rotating emission beams, please view
these AVI animations courtesy of Prof. Kazumasa Imai
of the Kochi National College of Technology in Japan: #1
(3.2 MB), #2
(3.7 MB), #3
(3.7 MB), #4
(6.9 MB).
Woodpeckers
and Ocean Waves
When it comes to sound effects, woodpeckers and ocean waves can't hold
a candle to Jupiter.
Jovian radio bursts come in two basic
varieties: "L-bursts" sound like ocean waves crashing on a (very) distant
beach. "S-bursts" produce a rapid-fire popping sound with a quasi-periodic
beat that reminds some listeners of woodpeckers. Slowed down by a factor
of 128:1, "S-bursts" sound like eerie, drifting whistlers. The "L" in
L-burst stands for "long;" the "S" in S-burst stands for "short," after
the way each sounds in the loudspeaker of a ham radio.
Jupiter Easy Listening
Center
| These colorful dynamic
spectra show the frequency components of 25 MHz radio bursts from
Jupiter captured on tape at the University of Florida
Radio Observatory. Click on the images for better views and an
explanation of the spectra. Click on the links below to listen to
the giant planet's sounds. |
S-bursts
 |
L-bursts
 |
Above: S-bursts sound like a staccato series of pops
through the loudspeaker of a shortwave receiver. Slowed down by a
factor of 128:1, they produce an eerie whistling tune. Listen to
sample S-bursts by clicking on one of these links. Normal
Speed [RealAudio] [mp3]
Slowed
Down [RealAudio] [au] [wav] |
Above: L bursts sound a little like waves crashing on
a beach. Listen to sample L-bursts by clicking on one of these
links. [RealAudio]
[au] [wav]
[mp3]
Having troubles playing these
sounds? You may need to download
the RealAudio player or an MP3 player. |
 Bonus Track:
Like Jupiter, the Sun is a
powerful source of radio bursts at shortwave frequencies. To hear an
example of an 18 MHz solar burst, download this
two-minute audio track and play it using an MP3 player. (Credit: The University of Florida Radio
Observatory) |
A Radio JOVE Tailgate Party
One of the first Radio JOVE student teams, at the Lexington
Traditional Magnet School in Lexington, Kentucky, made a successful
observation of Jupiter late last year. On the night of October 22, 1999,
students, teachers and parents set up an observing station in Mt.
Sterling, Kentucky, on a farm far from any electrical interference. They
arrived early enough to enjoy a festive cook-out before the late night
observations began. It was the first-ever Radio JOVE tailgate
party!
Later that night Jupiter came through very strong and
clear, surprising even long-time Jupiter observers with its intensity.
 Right: Students from the
Sonoma Valley High School in Sonoma, CA, pose next to their completed
Radio JOVE radio-telescope kit, consisting of a 20.1 MHz receiver
and dual phased dipoles. Students in Kentucky used classroom-built
equipment like this to record Jovian radio bursts on October 22,
1999.
"At first, when I heard about the Radio JOVE project, I thought it
would be interesting to listen to storms on Jupiter," wrote Nazrana Karim,
a student at the Lexington Traditional Magnet School. "We had to meet
after school two days a week to construct the radio telescope. It wasn't
that hard, but we put a lot of effort into it and we built a great
antenna.
"We put the antenna up twice for the media and once for the real thing.
[The big day] was awesome. We had a party and then, at 2:00 AM, we went
out to [our teacher] Mr. Salmons' farm to listen to Jupiter.
"I can't exactly describe the sound. It was like a hurricane - only
there were outbursts and explosions. I had a great time and I realize that
an opportunity like this [might] only come along once in a lifetime."
Virtual Radio Jove
"We recommend that Radio JOVE participants build the kit and
make their own observations," says Jim Thieman. "But we realize that some
schools won't be able to do that, so a second way of participating is to
get data
online from the University of Florida Radio
Observatory. (UFRO)."
 The UFRO, located in a
central Florida pine forest near the mouth of the Suwannee river, hosts an
array of unusual-looking antennas designed to capture signals from Jupiter
and the Sun at shortwave frequencies. Led by University of Florida
Professors Alex Smith and Thomas Carr, scientists and graduate students
have been collecting radio data from Jupiter at the UFRO since the
mid-1950's. It's North America's premier facility for low frequency
planetary radio astronomy, and now it's about to go online.
"By the fall of 2000 we'll have live streaming audio sounds as well as
total power measurements for 7 spectral channels from 18 to 32 MHz, which
is the optimum range for observing Jupiter from ground based stations,"
says Francisco Reyes, the director of the UFRO.
Above: This 18 MHz
"crossed-Yagi" pictured on a cloudy day in central Florida is an
over-sized ham radio antenna that scientists at the University of Florida
use to measure polarized radio bursts from Jupiter. It's just one of many
exotic radio antennas at the UFRO, including an 8 acre array of
26 MHz dipoles, an 18-32 MHz
log spiral array, and many more towering Yagis.
Jupiter
won't be far enough from the Sun to allow useful shortwave observations
for another few months.
"We're really gearing up for autumn," says
Thieman. "In the meantime, since we can't observe Jupiter very well, we're
observing the Sun instead."
Like Jupiter, the Sun is a powerful source of shortwave radio bursts.
Solar radio activity is especially high now with the solar maximum
expected to begin sometime in the year 2000.
"Recording solar
bursts is a great way to test the completed radio telescope kits," says
Thieman, "and it's great fun for the kids to listen to. It's also a good
opportunity for them to learn about the powerful processes that produce
solar storms and flares."
Stay tuned to Science@NASA for more information and updates about
Radio JOVE and and radio emissions from Jupiter.
Radio JOVE is
supported by the Goddard Space Flight Center Director's Discretionary Fund
and by a Space Telescope Science Institute IDEAS Program Grant. Team
members include scientists and educators from NASA, the University of
Florida, the Florida Space Grant Consortium, RF Associates, The INSPIRE
Project, Inc. and Raytheon ITSS, |
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