Another of the more bizarre features on the Martian surface

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."