Novel spots found on Jupiter (Forwarded)

American Geophysical Union

AGU Contact:
Peter Weiss
Public Information Manager
Phone: +1-202-777-7507

University of Liége Contact:
Didier Moreau
Service Presse & Communication
Phone: +32 (0) 4 366 52 17-18

Contact information for coauthors:
Bertrand Bonfond, +32 (0) 4 366 97 72

17 March 2008

AGU Release No. 08-09

Novel spots found on Jupiter

WASHINGTON -- 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 Liége 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 Liége
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.

Notes for Journalists

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this paper by clicking on this link:
http://dx.doi.org/10.1029/2007GL032418

If you need instructions for downloading, please see:
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Images:

High-resolution, digital images related to the leading spot and a text
file providing captions and credit information are available at
http://lpap.astro.ulg.ac.be/~bonfond...ond_images.zip
or from Bertrand Bonfond (see contact information above).

Title:

"UV Io footprint leading spot: A key feature for understanding the UV Io
footprint multiplicity?"

Authors:

Bertrand Bonfond, J.-C. Gérard, D. Grodent, and A. Radioti
Laboratoire de Physique Atmosphérique et Planétaire
Université de Liége
Allée du 6 Août 17, B-4000 Liége, Belgium

S. Jacobsen and J. Saur
Institut für Geophysik und Meteorologie
Universität zu Köln
D-50923 Köln, Germany

Citation:

Bonfond, B., D. Grodent, J.-C. Gérard, A. Radioti, J. Saur, and S.
Jacobsen (2008), UV Io footprint leading spot: A key feature for
understanding the UV Io footprint multiplicity?, Geophys. Res. Lett., 35,
L05107, doi:10.1029/2007GL032418.