mars_landing_sites_001221 WASHINGTON -- Scientists have begun eyeing dozens of prospective landing spots for two Mars robots set to wheel across the Martian landscape in early 2004.
The
twin Mars Exploration Rovers are outfitted with special gear to search for evidence of liquid water that may have been present in the planet's past. 
The Athena science payload is expected to open a new chapter in Mars exploration.
The first of a series of landing-site workshops is to be held late next month at NASA's Ames Research Center in Mountain View, California.
Mars experts have begun wrestling with sites that meet two criteria: locations that yield high science returns and that won't spell double-trouble for the
twin spacecraft touchdowns.Attractive sites
Initially, upwards of 185 prospective Mars landing sites were under consideration, said Matthew Golombeck, Mars exploration program landing site scientist at the Jet Propulsion Laboratory (JPL) in Pasadena, California.
A recent request has been made of Mars scientists to help shorten the long list of interesting landing locales. That process has netted about 30 high-priority science sites, Golombeck told SPACE.com.
"It's really the first time that the first-order triage of sites could be done on the basis of science," contrasted to restrictions placed on sites due to spacecraft engineering issues, Golombeck said.
"There's actually a fair bit of consensus among the community about the kinds of sites they find particularly attractive," he said.
Next month's meeting at Ames will help sort out further what areas should be targeted by the now-orbiting
Mars Global Surveyor for detailed inspection. "Mars Global Surveyor has really revolutionized the data you can bring to bare on site selection," Golombeck said.
"You have to do whatever you possibly can do to learn about the surface before you engender a spacecraft's health to it," Golombeck said. "Having more information is better," he said.
First looks
The rovers are slated for individual launches from Cape Canaveral, Florida.
The first robot is to be sent Mars-ward on May 30, 2003 and the second one on June 27. They would then reach the Red Planet on January 4, 2004 and February 8, respectively.
Preliminary looks at rover abilities and other factors have led to prospective landing site ellipses for the Mars Exploration Rovers (MER), now tagged MER-A and MER-B.
~
Areas on Mars that are under consideration are within southern Isidis and Elysium Planitiae in the eastern hemisphere and western Arabia Terra, Terra Meridiani, Xanthe Terra and Chryse Planitia.
Furthermore, prospective landing locales at the bottom of
Valles Marineris in the western hemisphere have been identified, with spectacular viewing guaranteed.Scraping for science
Each of the nearly 300-pound (150-kilogram) rovers will tote
the Athena science payload, led by Steve Squyres from Cornell University in Ithaca, New York. The array of instruments will allow the rovers to serve as robotic field geologists."That's exactly what the rovers are," Squyres said.
Rocks and soil will be analyzed and a special device called the rock-abrasion tool will scrape away at objects of interest, exposing fresh rock surfaces for intensive study.
The rovers will have a lot of mobility, Squyres said. "We need to look at whether or not there are sites where this mobility can be used to particular advantage," he said. "The rovers are being designed to each range up to 110 yards (100 meters) per Martian day. If the health of the twin vehicles is good, surface operations may extend beyond late April 2004.
Squyres said that the prospects are high that the rovers can sample areas
where water-lain sediments may exist.Rover landing sites are to be finally selected about a year before launch, pegged to areas that show evidence of
ancient water, like former lakebeds."So basically, it's water...water...water. But it's not water now. It's water when and what was the environment," Golombeck said.
Follow the bouncing balls
Similar to the Mars Pathfinder landing system used in 1997,
airbags are to cushion the rovers on touchdown, after a parachute slow-down and high-altitude fall through the thin Martian atmosphere. When Mars Pathfinder first smacked into its target area, it then made 10 to 20 large bounces, covering about 1.2 miles (2 kilometers) distance in the process.
Scientists and engineers face a number of tough issues in precisely and safely touching down the Mars rovers. For instance, large slopes can spoof spacecraft landing radar. A false reading could cause premature or late firing of rocket motors and delay airbag inflation.
Sites must also be chosen that are at certain elevations. Adequate atmospheric density at select landing sites is critical for the parachute to slow down the lander after plunging through Mars' atmosphere.
Other variables include wind and dust, which can coat rocks and shorten the lifetime of rovers by covering power-providing solar panels.
Consensus building
Next month's gathering of Mars scientists at NASA's Ames Research Center will represent various science disciplines, such as biology, geology and chemistry.
~
Obtaining a happy mix of Mars interests is not always easy.
"We're going to be able to have some pretty lively discussions on where the best prospects are for landing," said John Grant, geologist with the Smithsonian's Center for Earth and Planetary Studies.
Grant is co-chair, along with JPL's Golombeck, of the Mars Landing Site Steering Committee.
There is no preordained magic number of sites that need to be identified stemming from the Ames gathering, Grant said.
"It would be desirable, certainly, to see a consensus that allows us to focus on some relatively small number of sites. We want to find out what the community has got to say," Grant said.
Final resting spots
Ron Greeley, planetary geologist at Arizona State University in Tempe, is an expert on landing site selection criteria.
"Safety, safety, safety," is at the top of Greeley's Mars landing site criteria list. "We have to land successfully," he said.
By using both Mars Global Surveyor, as well as data gleaned by Viking Mars orbiters in the 1970s, the number of candidate sites will be honed down, Greeley said.
High-resolution imagery and
other science data that Mars Global Surveyor will continue to churn out is key in picking the final touchdown spots for the twin Mars rovers. "That data will lead to either the rejection or the prioritization of the sites. So it's an iterative process," Greeley said.But clarity of vision to pick sites can also spark heated discussion.
"Yes, it could make the debates more interesting, shall we say," Greeley said.
advertisement
