Listening to
the 'sounds' of Jupiter
Monday, 18 December, 2000, 15:23 GMT
By BBC News Online science editor Dr David Whitehouse
Ripples
in magnetic fields wafting through interplanetary space
have been detected by a space probe and converted into
sound.
The "noises" were picked up
the Cassini spacecraft which is en route to Saturn in
2004 via Jupiter.
The probe is detecting waves in the
thin gas of charged particles that fills the space
between the Sun and its planets.
The waves are in low radio frequencies
and can be converted to sound wave frequencies to make
the patterns audible.
Listening to the "sounds" of
near-Jupiter space has been done before by the Pioneer
and Voyager probes of the 1970's, but this is the first
time that Cassini's data have been used in this way.
Oscillations
The waves were detected by Cassini's
radio wave and plasma science instrument on 8 December,
at a distance of about 23 million kilometres (14 million
miles) from Jupiter.
Scientists believe that they arise
from interactions between Jupiter's magnetic field and
the solar wind of particles streaming away from the Sun.
Researchers point out that valuable
information can be gleaned from this data. There are
oscillations discernible that are produced by so-called
ion-acoustic waves, the result of electrons pushed
around by the energy in Jupiter's bow shock region.
The bow shock is similar to a sonic
boom from a supersonic jet flying through Earth's
atmosphere. Near Jupiter, the bow shock is caused by the
superfast solar wind being diverted around Jupiter's
magnetic field. The solar wind is heated, slowed and
deflected.
Cassini has not yet reached Jupiter's
bow-shock - this should occur in a few weeks from now.
But the shock is probably the source of energy driving
the waves that are reaching the spacecraft.
