Scientists exploring Venus by robot have surveyed a chunk of the planet that includes a mountain seven miles high whose slopes are dusted with a "mystery material" that could be fool's gold, volcanic domes shaped like pancakes a half mile high and vast formations resembling horseshoes, believed to be unique in the solar system.

The spacecraft Magellan, using its advanced radar "eyes" to see more detail than ever before, has mapped about 18 percent of the surface of Earth's hot and toxic sister planet despite continuing communications gaps and other problems, the project's leaders at the Jet Propulsion Laboratory in Pasadena, Calif., said at a briefing yesterday. They also released six new photographs.

"We're seeing some really spectacular things," said R. S. "Steve" Saunders, Magellan project scientist. But he and others emphasized that this scenery is so new and alien that they are only beginning to figure out what it means.

They expect their discoveries to tell them more not only about Venus, the nearest planet, but also about Earth.

Rising abruptly seven miles above the planet's surface in a region known as Ishtar Terra is Maxwell Montes, the highest mountain on Venus.

Scientists theorize that it was formed by the same kind of compression forces that shaped the Himalayas on Earth.

On the slopes of this behemoth, scientists have detected a material of unknown composition. Using Magellan's radar to measure the strength of natural energy, or heat, being emitted from the planet's surface, they have revealed "tantalizing" new detail about the material's distribution, showing that it lies in areas that appear bright in visual images of the surface, according to G. H. Pettingill of the Massachusetts Institute of Technology, who heads the radar team.

Seeing such a signature on Earth, he said, scientists would assume it was ice or water. But at surface temperatures of 700 degrees Fahrenheit, that is not possible.

It is probably is a flaky metallic material, a good electrical conductor, he said, and the most likely candidates are iron pyrite -- called fool's gold because of its yellowish color -- or the iron minerals hematite and magnetite.

The new images also show horseshoe-shaped features 600 miles long by 300 miles wide, that could reflect sculpturing by incoming meteorites and high winds on the planet, according to the science team's Ray Arvidsen of Washington University in St. Louis.

At the core of the horseshoe formations are impact craters 10 to 15 miles wide. Shock waves triggered by the falling meteorites that caused the craters may have formed the first elements of the horseshoes by spewing debris in all directions, he said.

Some of the ejected material may have been caught by upper-level winds flowing east to west, accounting for fact that all the horseshoes are open toward the west.

The horseshoes are "unique in the solar system," he said.

The new images also show seven domes of volcanic lava, 15 miles across and 2,500 feet high, that look like pancakes or, perhaps, coconut macaroons, according to Saunders. They may have been formed by a viscous form of molten rock from deep inside the planet, he said.

"We've never seen this before," he said. "It will take a while to figure out."

Magellan was launched from the space shuttle Atlantis on May 4, 1989, and began its formal mapping job in orbit around Venus on Sept. 15. Scientists said yesterday they expect to map about 80 percent of the planet's surface by the end of the mission, as planned, despite problems with the spacecraft.

On Thursday, Magellan suffered a 40-minute blackout, the third time scientists have lost contact with the craft. They expect the problem, whose cause is uncertain, to occur again, but changes made recently in the onboard computer instructions have minimized the resulting loss of work time, according to project manager Anthony Spear.

Engineers are also working to fix a balky tape recorder, which has made it more difficult to convert the radar data into images of the Venusian surface, he said.