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 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
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.