Nasa is looking for space enthusiasts to help it find and classify craters on Mars.
Scientists at the American space agency's Ames Research Center want to recruit "clickworkers" who are happy to spend time looking through a series of images of the Martian surface and rating the craters they find.
Nasa is turning to people to do the job because they tend to be more discriminating than computer software designed for the same task.
If the pilot project proves successful, the clickworkers could be asked to help the agency process the huge amounts of data from Nasa's present and future Martian probes.
Crater clues
Late last year, a smaller experiment was started that asked people to classify craters photographed by the Viking Orbiter in 1976.
The test project used data that had already been studied to see if the layman was as good at spotting and classifying craters as Nasa's own scientists.
The rate at which craters degrade tells experts a lot about how geologically active a planet is and when and if water flowed on its surface.
More generally, craters can give clues about a planet's development and what future probes should be looking for.
Initially, in the new pilot study, clickworkers will be asked to look at images of the Martian surface, estimated to show 42,000 craters in a latitudinal band 30 degrees north to 30 degrees south.
Good job
The classifications by different clickworkers will be collated to ensure the ratings are consistent. It will also be established how many times an image has to be checked before results are reliable.
Bob Kanefsky, the Nasa software engineer running the web part of the project, said that, although some crater-raters missed some very faint features, generally they did a good job.
Results from the project will be presented to other planetary scientists in a few months, he said.
"We'll see if the idea catches on and researchers decide to use this idea for other types of space data analysis."