For those who want to explore Mars but can't wait for a spacecraft to take them there, NASA scientists have reformulated a website that lets the general public search data and images from previous missions.

The website called Marsoweb had been designed to help scientists select possible landing sites for the Mars Exploration Rovers. By making the web pages more user friendly, NASA hopes that space enthusiasts will electronically survey the red planet's terrain for interesting geological features.

However, many Mars lovers already know about the site. About a half million people have visited Marsoweb. "Armchair planetary astronomers probably found it through Google," said Glenn Deardorff, a computer scientists, who has worked on Marsoweb for over four years. In January, the site recorded 26.7 million "hits" when the first rover, Spirit, landed.

The updated pages offer a number of computer tools. On a global map taken during the Viking mission, users can zoom in on certain spots that were imaged by the Mars Orbiter Camera with a resolution between two and 12 meters per pixel. Included with the visual images are topographical, geologic and thermal inertia maps. The thermal inertia, which quantifies how a material holds and conducts heat, gives researchers an estimate of the granularity of the surface.

Also on display are the candidate landing sites for the Mars Exploration Rover 2003 missions. Laypersons can try to discern the selection process that mission organizers went through. "It isn't easy to find an overlap," Deardorff said, "between something scientifically interesting and a good landing spot from an engineering perspective."

In the coming month, Deardorff expects some performance upgrades that will once again allow virtual adventurers to swoop over swaths of recreated 3D Mars terrain. Currently, there are some pre-programmed fly-bys over the equatorial region that are available, but soon users will be able to select their destination from anywhere on the planet.

In some ways, Marsoweb is a test bed for the software that will be needed for the High Resolution Imaging Science Experiment (HiRISE), scheduled to go up with the Mars Reconnaissance Orbiter in 2005. HiRISE should be able to view objects on the surface with one-meter resolution, which will allow better identification of geological features. The public will be able to peruse these images and put in requests for follow-up observations. For this reason, NASA is touting HiRISE as "the people's camera."

http://marsoweb.nas.nasa.gov/landingsites/index.html