Jupiter: A Cloudy Mirror for the Sun?

http://www.pparc.ac.uk/Nw/XMM_Jupiter.asp

Jupiter: A cloudy mirror for the Sun?
Particle Physics and Astronomy Research Council
March 7, 2005

Astronomers using the European Space Agency's XMM-Newton telescope have
discovered that observing the giant planet Jupiter may actually give
them an insight in to solar activity on the far side of the Sun! In
research reported in the most recent edition of Geophysical Research
Letters, they discovered that Jupiter's x-ray glow is due to x-rays
from
the Sun being reflected back off the planet's atmosphere.

Jupiter is an intriguing object when viewed in x-rays; it has dramatic
x-ray auroras at the poles and a variable x-ray glow from near the
equator. Researchers had theorised that these x-rays from the
equatorial
regions of Jupiter, called disk x-rays, were controlled by the Sun. In
November 2003, during a period of high solar activity, they observed
Jupiter.

"We found that Jupiter's day-to-day disk x-rays were synchronised with
the Sun's emissions," says Dr Anil Bhardwaj, from NASA Marshall Space
Flight Centre and lead author on the paper. "Unfortunately, we missed a
relatively large solar flare during the 3.5-days observation due to the
perigee passage of the XMM-Newton". "But, still we were lucky;
particularly clear was a signature of a moderate solar flare that went
off during the observing period - there was a corresponding brightening
of the Jovian disk x-rays", says Anil Bhardwaj.

In addition to supporting the researchers' theory, this result has
another application - in studying the Sun. The Sun is a very dynamic
environment and processes there have an impact on human activities. For
example, solar flares (the most powerful explosions in the solar
system)
can damage satellites or injure astronauts in space, and on Earth they
can disrupt radio signals in the atmosphere, so it is important to
understand as much as we can about them.

There are several dedicated spacecraft watching the Sun (such as the
European Space Agency's SOHO satellite), as well as ground-based
telescopes, but there are gaps in coverage as some areas of the Sun are
not visible by any of these means at some times.

"As Jupiter orbits the Sun, we hope to be able to learn more about the
active areas of the Sun we can't see from Earth by watching the Jovian
x-ray emissions," says Dr Graziella Branduardi-Raymont from the
University College London's Mullard Space Science Laboratory. "If a
large solar flare occurs on an area of the Sun that is facing Jupiter,
we may be able to observe it in light scattered from Jupiter, even if
we
cannot see that region of the Sun from around the Earth at the time."

Jupiter's atmosphere is not a perfect mirror of the Sunlight in X-rays
-
typically one in a few thousand x-ray photons (packets of light) is
reflected back, but the more energetic the photons, the more are
reflected into space.

UK participation in this research and the UK subscription to the
European Space Agency are funded by the Particle Physics and Astronomy
Research Council (PPARC).

Notes for Editors

The paper 'Solar Control on Jupiter's equatorial X-ray emissions: 26-29
November 2003 XMM-Newton observation' was selected as an AGU Journal
Highlight of Geophysical Research Letters, VOL. 32, NO. 3, 2005

What are solar flares?

A solar flare is a tremendous explosion on the Sun that happens when
energy stored in 'twisted' magnetic fields (usually above sunspots) is
suddenly released.

In a matter of just a few minutes they heat material to many millions
of
degrees and produce a burst of radiation across the electromagnetic
spectrum, including from radio waves to x-rays and gamma rays.

Images (click on pictures to get high resolution versions)

Solar flare.jpg
Credit ESA The solar flare of 2 April 2001 observed by the EIT on SOHO

XMM_terr.jpg
Artist's impression of XMM-Newton, Credit ESA

Graticule.jpg
XMM-Newton EPIC-pn image of Jupiter, slightly blurred, to show the
distribution of X-ray energies: lowest energies are shown in red and
the
highest in blue, with green in between. The graticule shows Jupiter's
orientation at the time of the observation and lines of latitude and
longitude (from Branduardi-Raymont et al. 2004)

Jupiter_image_1.jpg
Image of Jupiter, taken with the XMM-Newton EPIC-pn camera, clearly
showing the auroral zones (light blue) and the disk X-rays (darker).
(Courtesy ESA)

Contact details

Dr Graziella Branduardi-Raymont
Mullard Space Science Laboratory
Tel +44 1483 204133

Dr. Anil Bhardwaj
NASA Marshall Space Flight Center
Tel +1 256 961-7852 (work)
Alternative email:


Julia Maddock
PPARC Press Office
el +44 1793 442094


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