Solar wind whips up auroral storms on Jupiter and Saturn (Forwarded)

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SOLAR WIND WHIPS UP AURORAL STORMS ON JUPITER AND SATURN

Studies of Jupiter's auroras by scientists from the University
of Leicester have challenged current theories about the
processes controlling the biggest light-shows in the Solar
System.

The scientists compared a series of ultraviolet images of
Jupiter's auroras taken by the Hubble Space Telescope with
simultaneous measurements taken by Cassini showing conditions
in the solar wind as the spacecraft flew past the giant planet
in December 2000 - January 2001. They found that there was a
strong correlation between the strength of the solar wind and
the behaviour of the aurora that occurred towards the planet's
poles. Until now, scientists had believed that Jovian auroras
were caused by the planet's rapid spin and a stream of material
emitted from the volcanic moon Io at the rate of one tonne per
second.

"The argument is certainly not cut and dried", said Dr Jonathan
Nichols, who is presenting the results today at the Royal
Astronomical Society's National Astronomy Meeting. "Previous
work by our group has shown that Jupiter's main auroral oval is
not caused by the same type of processes that cause the Northern
Lights on Earth. However, this new study shows that the auroras
located polewards of the main ovals are directly linked to the
strength with which the solar wind is blowing, which means that
Earth-like processes are causing these polar auroras.
Surprisingly, we've also found that the main oval also shows a
direct correlation to solar wind strength, which is completely
the opposite result to the one we were expecting from our
predictions."

The results indicate that substantial energy is transferred from
the solar wind to the planet and this may account for the puzzle
as to why Jupiter is significantly warmer than it 'should' be.
The new findings may affect theories surrounding other aspects
of the Jovian magnetosphere, such as the mechanism by which
the plasma originating from Io is lost from the system and
determining the length of Jupiter's huge comet-like magnetic
tail.

In the same session, Sarah Badman will be presenting results of a
study of Saturn's auroras carried out over three weeks in January
2004. This study also combined images taken by the Hubble Space
Telescope with measurements of the solar wind recorded by Cassini
as it approached the ringed planet. Miss Badman collated all
available images of Saturn's aurora and determined, for the first
time, the most common shape and position of the aurora, as well
as the occurrence of more unusual features. Her findings
corroborate the theory that Saturn's auroras are caused by the
explosive release of solar wind energy that is built up and
stored in the planet's magnetic field.

FURTHER INFORMATION

The Earth's auroras are caused by the interaction of the planet's
magnetic field with the solar wind, a stream of charged particles
emitted by the Sun at roughly a million miles per hour. Some of
these charged particles are able to 'leak' into the magnetosphere
and are channelled into the high polar atmosphere, where they
interact with electrically charged air molecules, releasing
light. The brightness of the Earth's auroras therefore depends
on the rapidly changing conditions in the solar wind.

The magnetic field of Jupiter is five times larger than the Sun
and the auroras illuminating the Jovian atmosphere are up to a
hundred times brighter than those on Earth. The main oval
auroras are formed by a hundred million amps of electric current
flowing around the magnetic field and into the atmosphere as a
result of Jupiter's attempt to keep plasma emitted from its moon,
Io, rotating at the same velocity as the planet. Until now, it
has been thought that the system is completely dominated by this
rotation, and that the energy imparted by the solar wind is
negligible by comparison.

Like Jupiter, Saturn also possesses an enormous magnetic field
and exhibits bright auroral displays. Early, infrequent images
taken by previous spacecraft flybys and HST showed a narrow oval
of emissions with some varying brightness. The images taken in
January 2004 showed several unexpected features, including
spirals of aurora around Saturn's pole (compared to the oval
shape at Earth), bright 'blobs' of aurora that rotate around the
pole, and a unique auroral 'storm' where half the polar region
was totally filled-in with very bright auroras. Work at
Leicester has shown how these different auroral forms are
controlled by the interaction of the solar wind with Saturn's
magnetic field.

IMAGES

For images of Jupiter and Saturn's auroras, see:
http://www.ion.le.ac.uk/~jdn/hst/index.html

NOTES FOR EDITORS

Royal Astronomical Society's National Astronomy Meeting

The 2006 RAS National Astronomy Meeting is hosted by the
University of Leicester. It is sponsored by the Royal
Astronomical Society, the UK Particle Physics and Astronomy
Research Council (PPARC), the University of Leicester and the
National Space Centre, Leicester.

Space Plasma Physics at Leicester

The Radio and Space Plasma Physics Group at the University of
Leicester is the largest in the UK, with approximately 40 members
including academic staff, technical and support staff, research
fellows, and research students. The group's research programme
concerns the study of the outer plasma environment of the Earth
and other planets, including the interactions of planets'
ionospheres and magnetospheres with the solar wind plasma and
the neutral layers of the atmosphere below.

For more information see:
http://www.ion.le.ac.uk/index.html

Cassini-Huygens

Cassini-Huygens is an international collaboration between three
space agencies. Seventeen nations contributed to building the
spacecraft. The Cassini orbiter was built and managed by NASA's
Jet Propulsion Laboratory. The Huygens probe was built by the
European Space Agency. The Italian Space agency provided
Cassini's high-gain communication antenna. More than 250
scientists worldwide are studying the data streaming back
from Saturn on a daily basis.

Cassini-Huygens was launched in 1997 and went into orbit around
Saturn on 1 July 2004. In order to reach Saturn, the spacecraft
needed gravity assist boosts from the Venus, the Earth and
Jupiter. From 1 October 2000 to 31 March 2001, Cassini's
instruments were used to study Jupiter as the spacecraft
approached the sunlit side and receded from the dark side of
the planet. Cassini-Huygens reached the closest approach of
the flyby on 30 December 2000 at a distance of 10 million
kilometres from Jupiter.

Hubble Space Telescope

The Hubble Space Telescope is a project of international
cooperation between NASA and the European Space Agency. The
Space Telescope Science Institute in Baltimore conducts Hubble
science operations. The Institute is operated for NASA by the
Association of Universities for Research in Astronomy, Inc.,
Washington.

Jupiter Millennium Flyby

From the 14 December 2000 - 21 January 2001, researchers carried
out a joint campaign with Cassini and the NASA/ESA Hubble Space
Telescope, gathering simultaneous data and images of Jupiter's
auroras. Cassini's instruments, including the Cassini Plasma
Spectrometer (CAPS), Magnetometer (MAG), Ion and Neutral Mass
Spectrometer (INMS), measured the solar wind to determine the
pressure exerted by these winds on Jupiter. Hubble's STIS (Space
Telescope Imaging Spectrograph) instrument was used to capture
detailed ultraviolet images of the aurora.

Contacts

Dr Jonathan Nichols
Radio and Space Plasma Physics Group
Department of Physics and Astronomy, University of Leicester
University Road, Leicester LE1 7RH, United Kingdom
Tel: +44 (0)116 252 5049

Miss Sarah Badman
Radio and Space Plasma Physics Group
Department of Physics and Astronomy, University of Leicester
University Road, Leicester LE1 7RH, United Kingdom
Tel: +44 (0)116 252 1302