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AN X-RAY image of the planet Saturn is baffling astronomers. The image, snapped by NASA’s Chandra X-ray Observatory, looks dramatically different from Chandra’s earlier images of its gas giant sister, Jupiter.

Chandra’s Jupiter images showed bright X-rays coming from the poles. They are thought to come from solar particles bombarding the planet’s atmosphere as they flood in towards the magnetic poles, a process that also creates auroras.

Saturn’s X-ray profile, released last week, is just the opposite, with the X-rays concentrated mainly around the equator. That’s a surprise, because Saturn has bright auroras near its poles, just as Jupiter does.

The spectrum of Saturn’s X-rays looks similar to that of X-rays from the sun, suggesting they are reflected solar radiation. For that to be happening, Saturn’s surface would have to reflect solar X-rays astonishingly efficiently, about 50 times better than the moon – a finding that could shed light on the chemistry of Saturn’s outer layer.

Meanwhile the planet’s huge ring system, so spectacular at visible wavelengths, does not seem to reflect X-rays at all. That’s a surprise, says team member Scott Wolk. He says this means there must be no particles in the rings smaller than grains of sand, because smaller particles would scatter the sun’s X-ray radiation and show up strongly.