The Magellan spacecraft has found sand dunes on Venus despite low wind and little loose sediment on the planet.

"They look a lot like sand dunes on Earth," said Ray Arvidson, a geologist from Washington University in St. Louis and a Magellan scientist at NASA's Jet Propulsion Laboratory."This is a fairly rare occurrence on Venus," he said Wednesday. "This area just had a beautiful supply of sediment to be reworked into dunes."

Magellan's pictures revealed the dune field in an area of Los Angeles-size meteorite craters. The field is 30 to 40 miles long, and each dune is hundreds of yards wide, Arvidson said. Magellan hasn't determined their height.

Magellan's images have shown Venus has very little loose sediment. That's because the planet lacks water to erode rock.

Surface winds on Venus measure only a few miles per hour, but the atmosphere is so dense that even such light winds can lift sediment, he said. Atmospheric pressure on Venus' surface is 90 times the pressure at sea level on Earth.

Arvidson said the sediment that was blown around to form the dunes may have stemmed from a meteorite impact that shattered or melted rock. Another possibility is that the meteorite was a water-rich comet, he added.

Magellan bounces radar off Venus to make pictures and maps of the planet, which can't be photographed with optical cameras because of its thick cloud cover.

The pictures have shown numerous volcanoes, volcanic collapse craters, long rivers of solidified lava, extensive faults, deep valleys and towering ridges.