Novel Spots Found On
Jupiter
(18 March 2008) Scientists have
observed unexpected luminous spots on Jupiter caused by its moon
Io.
Besides displaying the most spectacular volcanic activity in
the solar system, Io causes auroras on its mother planet that are similar to
the Northern Lights on Earth. The auroral emissions linked to the volcanic moon
are called the Io footprint.
From previous studies, researchers had
found the Io footprint to be a bright spot that is often followed by other
auroral spots. Those spots are typically located downstream relative to a flow
of charged particles around the giant planet. Now, a team of planetologists
from Belgium and Germany have discovered that Io's footprint can include a
faint spot unexpectedly upstream of the main spot.
Each appearance of
such a "leading spot" occurs in a distinctive pattern, the scientists say: When
the main footprint is preceded by a leading spot in the northern or southern
hemisphere of Jupiter, it is also followed by downstream spots in the opposite
hemisphere.
"Previously, we only observed downstream spots, but only
half of the configurations of Io in the Jovian magnetic field had been
studied," says Bertrand Bonfond of the University of Liege in Belgium, who is a
member of the team that found the new type of spot. "Now we have the complete
picture. The results are surprising because no theory predicted upstream
spots."
Like a rock in a stream, Io obstructs the flow of charged
particles, or plasma, around Jupiter. As the moon disrupts the flow, it
generates powerful plasma waves that blast electrons into Jupiter's atmosphere,
creating the auroral spots.
The finding of the leading spot puts all the
previous models of the Io footprint into question, Bonfond says. He and his
colleagues propose a new interpretation in which beams of electrons travel from
one Jovian hemisphere to the other.
The new results were published
online on 15 March in Geophysical Research Letters, a journal of the American
Geophysical Union. The 16 March print edition of the journal features an image
from the study on its cover.
For this latest Io-footprint analysis,
Bonfond and his colleagues at Liege and at the University of Cologne in Germany
used the Hubble Space Telescope to observe Jupiter in ultraviolet
wavelengths.
New insights regarding Io-Jupiter interactions could apply
to other situations in which an electrically conductive body--in this case,
Io--orbits near a magnetised body, Bonfond says. Such configurations could be
very common in the universe. For example, some of the recently discovered
exoplanets that orbit stars other than the Sun are thought to be in such
configurations with their parent stars.
Our Moon does not create a
footprint on Earth because the Moon is not conductive and is also too far from
the Earth, Bonfond notes.
In order to test their new theory of how
leading and downstream spots form, Bonfond and his colleagues plan further
observations of Io's footprint after August 2008. That's when repairs and
improvements to the Hubble Space Telescope are scheduled to
occur.
(source: American Geophysical Union)
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