Scientists have used an orbiting Mars craft to photograph robotic landers that have been sitting dormant on the surface of the Red Planet since their missions ended.
Using a newly developed trick, the researchers imaged Mars Pathfinder, which in 1997 thrilled Earthlings with its photographs and the wandering science exploits of its Sojourner rover. Pathfinder appears as a dark dot near a rock that scientists named Yogi during the mission.
The Viking 1 lander from 1976 is also visible, as a bright dot in a separate image.
The photographs were made with NASA's Mars Global Surveyor. Normally it can resolve features only down to about 3 feet (1 meter) per pixel, not good enough to discern a typical landing craft from its surroundings.
The new technique involves "pitching the spacecraft at a rate faster than the spacecraft moves in its orbit around Mars," said scientists at Malin Space Science Systems, which operates the orbiter's camera. The resolution of images — across one dimension of the photograph only — is improved to about 20 inches (50 centimeters) per pixel.
The method, called image motion compensation, was developed during 2003 with the goal of photographing the Mars Spirit rover, which landed earlier this month, and its twin, Opportunity, slated to arrive later in January.
Scientists plan to use radio data and on-site observations from Spirit, and then couple that with the new imaging technique in coming days in order to pinpoint its location and more intelligently pick science targets for the rover to study.
The technique works only "when the location of the lander is already fairly well-established," Malin scientists said. They match known features — such as the rock named Yogi near Pathfinder — with features spotted in the image to help pin down whether a dot is the craft they're looking for.
"It would be extremely difficult to find a lander for which the location is uncertain," Malin scientists said in a statement.