Fred Scarf is one of the few people on Earth who listens to the song of other planets and the only one who synthesizes them into the "music of the spheres." The TRW Inc. scientist has an instrument on the National Aeronautics and Space Administration's (NASA) Voyager 2 spacecraft which he describes as "sort of a car radio antenna attached to a tape recorder." This picks up the radio waves generated in the vicinity of the spacecraft. Lately, Dr. Scarf has rigged up a microcomputer and music synthesizer to turn the noise of space and planets into a "Star Wars"-style siren song.
(His instrument, known as the Plasma Wave Detector, was not one of those affected by Voyager's recent problems. Over the weekend the Voyager flight team got the Lazy Susan-type platform that held the spacecraft's cameras and several other instruments operating predictably again. Following a series of tests, they now believe some dust or debris may have been caught in the gears. When the spacecraft cut across the plane of Saturn's rings Aug. 25, the plasma detector picked up a brief and extremely intense burst of noise that Dr. Scarf interprets as caused by a hail of tiny dust particles falling on the spacecraft.
Normally, the sounds that Dr. Scarf records have an eerie quality. Delicate, crystalline tones; bird-like chirps; deep, booming notes, and piercing whistles weave in complex and haunting patterns. Gustav Holst -- composer of the symphony "the Planets" -- would have been edified.
Actually, Dr. Scarf acknowledges, if you were riding on the distant spacecraft that has just looped by Saturn and begun its five-year journey to Uranus, you wouldn't hear much. The interplanetary void is as silent as you might imagine. However, this same space is noisy in radio frequencies; Dr. scarf simply is converting this inaudible cacophony into audible sounds.
In the almost-empty space between planets, radio noise is caused by the solar wind, the current of electrically charged particles -- electrons, protons, and ions -- that stream continuosly outward from the Sun.
Dr. Scarf also has an instrument on the International Sun Earth Explorer, which sits in space just sunward of Earth. On one tape he has synthesized the onset of a solar storm, and intense burst of charged particles which can interfere with communications and electrical power grids on Earth. Four or five hours before the storm strikes our home planet, the satellite detects warbling tones presaging the storm. "As a result we can give several hours warning rather than only a half hour," Dr. scarf explains.
The radio music of the planets has a more complicated origin. Many planets, including Earth, Jupiter, and Saturn, are surrounded by an invisible magnetic atmosphere, called a magnetosphere.
Although this magnetic atmosphere is intangible, it is extremely important. Some animals, and possibly even humans, unconsciously sense the magnetic field and so have an innate sense of direction. Without a magnetosphere a compass would not point north and the northern and southern lights would not exist in their present form. Even more importantly, the magnetosphere protects Earth's surface from cosmic rays and other potentially damaging radiation from outer space.
"Without a magnetosphere, life would have evolved in a totally different fashion," explains Dr. Scarf.
In addition, the magnetosphere gives Earth its natural radio voice. Earth for instance, emits an unearthly "chorus." At least this is the nickname that scientists have given the chirping, birdlike vibrations that emanate from the region above the aurorae.
"Jupiter was quite familiar," explains Dr. Scarf, recalling what his instrument on the Voyager spacecraft found when it flew by Jupiter two years ago. The main difference was that Jupiter is much, much bigger than Earth and so was its magnetic envelope.
A planet's magnetic field creates this music by its effect on electrically charged particles. These oscillate in a magnetic field in a similar fashion to a guitar string vibrating when plucked. The electrons are the lightest particles so they make the highest-pitch sounds. Protons are the tenors in the celestial chorus while heavier ions are the bases.
Of all the magnetospheres he has encountered, Dr. Scarf considers Saturn's the strangest and most mysterious. Saturn actually "rings" at certain, piercing tones. Sometimes these persist for long times. At others they turn off and on frequently.
According to Dr. Scarf's fellow experimenter, Don A. Gurnett of the Iowa State University, there is some evidence that this may be one of Saturn's moons "singing" to its parent planet.
Also, their radio ears have picked up wild chirps, whistles, and moans unlike any other planet. These are thought to be related to the physical rings. The rings are thought to carve out a big void from the center of the magnetosphere and this acts as a whispering gallery.
Saturn's music also differs substantially from that of Earth and Jupiter, the scientist reports. It is slow and deep, like a quartet of giant bass fiddles, he says.
The synthesized version of the Voyager 1 spacecraft flying past Saturn's planet-sized moon, Titan, is perhaps the most dramatic piece of celestial music that the scientist has. Deep, throbbing tones build in intensify to an almost unbearable level until, a little like Ravel's Bolero, the sound abruptly cuts off, followed by almost total silence.
Less musical, perhaps, but definitely peculiar, is the fact that Saturn itself gives off regular bursts of radio static in addition to its magnetosphere.
Jupiter and Earth both exhibit similar radio outbursts, but both of these planet's have a magnetic field that is oriented at an angle to their axis of rotation. This causes their magnetic field to focus high-energy particles on specific spots in their upper atmosphere, a process that gives rise to the radio noise.
On Saturn, however, the magnetic field has appeared to coincide with the planet's spin axis, making it difficult to explain why only a specific spot would generate radio frequencies when it rotated into the Sun.
Now, Voyager scientists believes they have found a very slight tilt to the magnetic field. It is only one-twelfth that of Earth's, but it might be enough to explain the radio bursts. According to Dr. Norman Ness of NASA's Goddard Space Flight Center, more work is required to pin down the direction of this tilt relative to the active radio region. But if Saturn's radio turns on when the magnetic field "nods" in the direction of the Sun, then the radio bursts will be explained.
Now dr. Scarf and his fellow scientists must wait five years until the spacecraft reaches Uranus. Then they will try to record the voice of this even more-distant world. In the meantime, he intends to try to synthesize the sounds of Venus.The US has a satellite in orbit around Venus and he will try to make some music out of the radio signals this probe encounters as it orbits Earth's veiled twin.