MRO snapped this image of boulder-strewn terrain in the martian
arctic. Originally, this area was the top candidate for the Phoenix
spacecraft’s landing site. Mission planners have now shifted
focus to less-rocky terrain. NASA/JPL/University of Arizona
If you were in charge of landing the next spacecraft on Mars, where would you choose to go? The scientist in you likely would argue for a geologically or biologically attractive site. But the flight engineer in you would hesitate to spend hundreds of millions of dollars on a mission that might not survive landing. The technology simply doesn't yet exist to land on a dime at, say, the rim of the Valles Marineris canyon system.
Likewise, NASA must weigh competing priorities whenever it wants to set down on Mars. The space agency's next opportunity will come in 14 months. The Phoenix mission, slated to launch this August, should land in the martian arctic in May 2008. Scientists chose a site in the far north because the Mars Odyssey orbiter has shown plenty of water ice just below the surface there.
Phoenix will dig through the soil to the ice below, bringing a mix of both onboard for sophisticated analysis. The bold objectives: to study the history of water in the martian arctic, and to search for evidence of a habitable zone and assess the biological potential of the ice-soil boundary.
But where in the vast arctic plains should Phoenix land? Last week at the 38th Lunar and Planetary Science Conference in Houston, planetary geologist Matt Golombek of NASA's Jet Propulsion Laboratory ran through the list of proposed landing sites and images of them taken by the high-resolution camera on Mars Reconnaissance Orbiter (MRO). The image of what had been the preferred site (that's it above) caused Golombek to say: "What you cannot see, can hurt you."
Those little black spots are the shadows of boulders big enough to cause trouble for the lander's base or solar panels. It's not the kind of place anyone would pick if there were a suitable alternative. Fortunately, there is. MRO imaged at least two other potential landing sites in the Vastitas Borealis Formation having rock abundances a factor of ten lower than in this site. Both offer Phoenix a high probability of successfully avoiding hazardous rocks. And that, my friends, will please both scientists and engineers.