SPACE.com -- X-ray Image of Saturn Puzzles Scientists

Chandra's image of Saturn held some surprises for the observers. First, Saturn's 90 megawatts of X-radiation is concentrated near the equator. This is different from a similar gaseous giant planet, Jupiter, where the most intense X-rays are associated with the strong magnetic field near its poles. Credit: X-ray: NASA/U. Hamburg/J.Ness et al; Optical: NASA/STScI

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	X-ray Image of Saturn Puzzles Scientists By SPACE.com Staff posted: 05:00 pm ET 08 March 2004

The first clear detection of X-rays from the giant, gaseous planet

Astronomers have gotten a good look at X-rays from the ringed planet Saturn, and they're puzzled by the results that defy current theory.

The image, made with NASA's Chandra X-ray Observatory, shows the X-rays are concentrated near Saturn's equator. X-rays from Jupiter, however, are concentrated mostly near the poles.

In results released today, Chandra observed Saturn for about 20 hours last April. The spectrum, or distribution with energy of the X-rays, was found to be very similar to that of X-rays from the Sun.

"This indicates that Saturn's X-ray emission is due to the scattering of solar X-rays by Saturn's atmosphere," said Jan-Uwe Ness, of the University of Hamburg in Germany. "It's a puzzle, since the intensity of Saturn's X-rays requires that Saturn reflects X-rays fifty times more efficiently than the Moon."

The observed 90 megawatts of X-ray power from Saturn's equatorial region is roughly consistent with previous observations of the X-radiation from Jupiter's equatorial region. This suggests that both giant, gaseous planets reflect solar X-rays at unexpectedly high rates. Further observations of Jupiter will be needed to test this possibility.

The weak X-radiation from Saturn's south-polar region presents another puzzle. Saturn's magnetic field, like that of Jupiter, is strongest near the poles. X-radiation from Jupiter is brightest at the poles because of auroral activity due to the enhanced interaction of high-energy particles from the Sun with its magnetic field. Since spectacular ultraviolet polar auroras have been observed to occur on Saturn, Ness and colleagues expected that Saturn's south pole might be bright in X-rays.

It is not clear whether the auroral mechanism does not produce X-rays on Saturn, or for some reason concentrates the X-rays at the north pole. The north pole was blocked by Saturn's rings during this observation.

Ness is lead author of a paper that will discuss the results an upcoming issue of the journal Astronomy & Astrophysics.

"Another interesting result of the observation is that Saturn's rings were not detected in X-rays," said co-author Scott Wolk of the Harvard-Smithsonian Center for Astrophysics in Cambridge, MA. "This requires Saturn's rings to be less efficient at scattering X-rays than the planet itself."

The same team detected X-radiation from Saturn using the European Space Agency's XMM-Newton Observatory. Although these observations could not locate the X-rays on Saturn's disk, the intensity of the observed X-rays was very similar to what was found with Chandra and consistent with a marginal detection of X-rays from Saturn reported in 2000 using the German Roentgensatellite ( ROSAT).

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