Isidis Planitia

Eos Chasma

Two backup sites wait in the wings in case there are problems found with the other sites: Isidis Planitia and Eos Chasma [image link]. The former sits close to some of the oldest material exposed on Mars, near the rim of a giant impact basin. The area is expected to be rich in very old rocks and so may provide clues to the early environment and whether it was watery or not.

Telecommunications Constraints

Telecommunications constraints will bear on the selection of the final two sites. The two rovers will communicate via the same Deep Space Network and Mars orbiter spacecraft antennas, so the rovers must be separated by at least 36 degrees in latitude so there will be no telecommunications overlap between the two. If Hematite is chosen as one of the sites, it is located far enough away from the other sites that there would be no overlap, said Golombek.

Choosing the Right Targets

In April 2002, the third landing site workshop will meet in Pasadena to share any new scientific information gained about the top sites, and to discuss and evaluate the safety of the sites with mission engineers. From the discussions, two sites will be selected for landing the two Mars Exploration Rover spacecraft.

A Little Help from Orbiter Friends

"This is a unique period where we have orbital missions that can help us make the selection," he said. Mars Global Surveyor's continuing presence at Mars, now coupled with Mars Odyssey, provides unprecedented tools to gather targeted information down to 3-meter resolution - about the length of a small sedan -- to help scientists make the landing site selection.

Golombek compares today's comparative wealth of detailed data with the relative paucity of information he had in selecting Pathfinder's landing site in the mid-1990s. Studying images from the 1970s-era Viking mission, "we had a hundred meter resolution for the Pathfinder landing site. That's about the size of a football field. Now, we're directing the Mars orbiter camera on Surveyor to get pictures of landing sites at 3-meters resolution. Our data sets for Mars are so new and growing so quickly. It's a very dynamic, exciting time for Mars exploration."

Suitable for Human Landing?

Though no human exploration missions are planned for Mars yet, Golombek says the landing site selections could be driven by different constraints. "For future astronauts, water would be a prime resource," he said, noting that the hydrogen and oxygen in water could be a source for rocket fuel for a return trip to Earth. "There could be a completely different suite of constraints that could take you to completely different sites than we're considering right now," he said.