Some of the most cracked, squeezed and stretched landscape yet seen on Venus has been captured in pictures made by the Magellan spacecraft, now halfway through its $744 million mission.

The planet's Alpha Regio volcanic highland "is an area that looks really tortured," said Steve Wall, Magellan representative at NASA's Jet Propulsion Laboratory.Brown University scientist Annette deCharon said that Alpha Regio's faults, mountain ridges and valleys constitute "some of the most complicated terrain we've seen in Magellan data."

The highland, a region where Venus' crust is unusually thick, now apparently is being stretched apart, possibly as it slumps toward surrounding lowlands, she said. Some of its valleys are filled with solidified lava flows.

Wall, deCharon and laboratory scientist Richard Goldstein displayed the pictures Wednesday on NASA closed-circuit television after Magellan passed the halfway point in its eight-month primary mission. No prints of the pictures were released.

The polar-orbiting spacecraft's mission is to use radar to make pictures of 70 percent to 90 percent of Venus' cloud-covered surface as the planet slowly rotates once on its axis. That takes 243 Earth days.

By Wednesday morning, the spacecraft had flown over 50.9 percent of the Venusian surface and successfully made pictures of 41.4 percent of the terrain, Wall said.

The 50.9 percent of Venus over which Magellan has flown equals an area that on Earth would stretch from Los Angeles east to Bombay, India, and from the North Pole to the southern tip of South America, Wall said.

On Wednesday, Magellan was mapping Aphrodite Terra, a continent-like highland the size of Africa that straddles Venus' equator.