Venus has 600-mile-wide circular bulges on its surface caused by molten rock pressing up from inside the planet, the same kind of forces that created Hawaii, a Magellan scientist says.

The bulges are as much as a mile high, said Ellen Stofan, a geologist who analyzes the spacecraft's pictures of Venus at NASA's Jet Propulsion Laboratory."You have hot material that rises from deep within the interior of the planet," pushing up overlying rock, she said. The process "happens over scales of hundreds of millions of years," she said Wednesday.

From a bird's-eye view, the bulges look like sets of concentric rings. The rings on the bulges are ridges and valleys. The bulges, called coronas, are dotted with numerous volcanoes and lava flows.

Stofan said the bulges are formed by the same kind of upwelling of molten rock that created the Hawaiian Islands.

On Wednesday, Magellan orbited Venus for the 551st time since arriving at the planet Aug. 10.

It has used its picture-making radar to peer through Venus' thick clouds during 288 of those orbits since mapping started Sept. 15. Magellan was launched from space shuttle Atlantis in May 1989.

Magellan is examining the planet with a sophisticated radar that makes detailed pictures and can calculate surface topography.