The basketball-size probes should have started sending radio messages through the Global Surveyor on Friday night.

Its companion, Global Surveyor, arrived a few months later and is producing the most detailed maps yet of the surface.

The discovery, another triumph for the Global Surveyor, demonstrates just how effective unmanned missions can be.

"The new pictures from Global Surveyor tell us part of the answer," he said.

Project officials said that aerobraking made Global Surveyor's navigation by far the most challenging for any planetary mission to date.

Now its success will be critical at the start of Global Surveyor's explorations.

Among other things, Global Surveyor has taken pictures of planet-scale dust storms, elaborate dunes and volcanoes.

Another $300 million went for the orbiting companion, Global Surveyor.

Global Surveyor is still going strong, returning the most detailed pictures ever for mapping the planet.

Soon enough, the controllers will be busy operating two vehicles at once, and the Global Surveyor as well.