Details of various MER sites were presented here throughout the week during the 33rd Lunar and Planetary Science Conference sponsored by NASA and the Lunar and Planetary Institute.
Pinning down terrain
Attention is being paid to several Mars locations: Melas Chasma, Isidis Planitia, Gusev crater, and the Sinus Meridiani Hematite Region.
Within each area, large landing ellipses have been divined, places where a rover cushioned in airbags can bounce, then come to a full stop and rev up science work. It's been a long game of pinning down terrain that offers good science, but is non-threatening to the rovers.
"We know more about these four locations than any other places," said Matt Golombek, Mars exploration program landing site scientist for the Jet Propulsion Laboratory (JPL) in Pasadena, California. He is also co-chair of the Landing Site Steering Committee.
Golombek said the Mars Global Surveyor's camera has snapped special images of each potential MER landing spot, and several backup sites. "We actually have geologic maps of the landing sites based on this incredible data set," he told SPACE.com.
Those maps will also prove useful in determining the whereabouts of each rover once down on Mars' surface. Furthermore, carefully orchestrated treks by the mobile rovers can be scripted using the maps.
Cold hematite: hot and bothered
Golombek said each of the four candidate landing zones have problems to some extent.
The most favored MER site is the hematite region, a place that shows evidence for processes involving water.
"The hematite site, which has looked like the perfect landing site, has finally fallen true to the salvo that there is no perfect landing site. There never is," Golombek said. On one hand, the area appears smooth, flat, and safe. From a landing point of view, that's nothing but good news.
But the site may be too cold, reducing the longevity of the rover, Golombek said. "It's not a concern for landingbut a concern afterwards. But we don't know if that is the case," he said.
Work is now ongoing to better characterize the hematite site. Mars Odyssey's sensors are expected to help certify the temperature profile of that area, Golombek said.
Dust devil tracks
As for the other sites, Gusev crater has been recently imaged too. It has been found to contain "dust devil" tracks. These ground traces are produced by whirlwinds, a telltale sign that means there's significant dust in that location.
"Dust can shorten the mission by getting on your solar panels. But also, scientifically, if there's enough dust it covers up things. So when you look around, you won't know what materials to go look at in detail because everything will look like this dust layer. So that's not good," Golombek said.
Melas Chasma is a spectacular site. Exploring it with a rover could help determine whether water-deposited sediments are located there.
But being at a bottom of a canyon, Golombek said, winds could play havoc with the spacecraft during parachute and airbag deployment sequences. Also, the mesas associated with Melas Chasma are slightly rougher than other landing sites.
Lastly, Isidis contains a worrisome field of rocks. "That's a real concern," Golombek said. Sharp rocks, small and large, can knife the MER landing airbags. Damage to the protective cushion of airbags during a rover landing could ruin your day.
Hard looks at soft touchdowns
Later this month, Mars scientists and space engineers are meeting in Pasadena, California to take another hard look at potential MER landing spots.
Ultimately, the selection of touchdown areas is a balancing act between "science wants" and "engineering needs" - a friendly but sometimes testy tension.
"A site can be too rockyor not have enough rocks," Golombek said.
Meanwhile, at JPL, the Mars Exploration Rovers are being assembled and tested. Spacecraft engineers are getting a better handle on how the MER robots best operate. That will feed back into determining where on Mars the robotic right stuff can do its stuff.
"It's an evolving process. You never get done beating yourself up," Golombek said. "We want to go to two different places. Doing that we'll get more diversity of what's really there on Mars," he said.
"You obviously want the rovers to be safe. You don't want to take chances with hundreds of millions of dollars worth of spacecraft. On the other hand, you want to address compelling science. And that's the nature of the landing site process," Golombek said.
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