The U.S. Geological Survey has just released and is selling a pair of Mars maps. One gives a detailed view of the red planet's topography and the other includes color-coded contour lines.

On the maps, you can pick out the landing sites of NASA's Spirit and Opportunity rovers, as well as those of the previous Viking and Pathfinder missions. Each map measures 36x32 inches. The set costs $14.

The maps are based on data from the Mars Orbiter Laser Altimeter (MOLA), an instrument on NASA's Mars Global Surveyor (MGS) spacecraft. A base image was created from more than 600 million measurements gathered between 1999 and 2001.

Finding the maps can be difficult at the agency's online store, so we had a marketing representative walk us through the process.

• Go to the store's main site, http://store.usgs.gov
• Click "Enter USGS Store"
• Then click on "Featured Products"
• Click on "Explore Mars Now" to see the ordering page
• To get more details about the map, click on its name on the ordering page

  -- Robert Roy Britt

  Credit: USGS/NASA