Jovian Bow Shock
All of the planets in the Solar System are embedded in the interplanetary
medium known as the solar wind. The solar wind travels supersonically
with respect to the slower planets at a speed of about one million miles
per hour. And, just as a supersonic jet will create a sonic boom in the
slower atmosphere of Earth, a bow shock is created in the solar wind
in front of each planet.
Jupiter has a strong magnetic field that reaches out more than 3.5
million miles in front of the planet, providing a substantial obstacle
to the flow of the solar wind. The bow shock forms at that surface in
interplanetary space where the supersonic solar wind encounters the
magnetic force of Jupiter and it acts to slow and deflect the solar wind.
In the process, the energy of motion of the solar wind is converted to
thermal energy at the bow shock, heating the particles behind the shock
and creating rapid and turbulent particle motions that generate the plasma
waves associated with the bow shock.
When the Voyager spacecraft encountered the Jovian bow shock, there was
a very sudden burst of intense, low-frequency emissions extending over a
wide range of frequencies. These emissions are directly associated with
the Jovian bow shock and are similar to the loud sound associated with
a sonic boom. The shock noise signature is a sudden, loud, rumbling roar
lasting more than a minute.
For more information, see the article,
Plasma Waves Associated with the Bow Shock of Jupiter, by
W. S. Kurth.
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Sounds of Space
Radio and Plasma Wave Research Group
The Department of Physics and Astronomy
The University of Iowa