A space project can take a decade to come to fruition, but then the funding often dries up. The relatively small amount necessary for post-mission data analysis is usually the hardest to come by: the media hoop-la has come and gone, and funding agencies want to develop new headline projects. Only an estimated 20% of the raw data collected in typical space missions is ever properly exploited.
A small group led by Dr Bob Kanefsky at Nasa-Ames Research Center in California is pioneering a new approach. They encourage members of the public to sift through space probe imagery of the surface of Mars, dating the different regions by using crater counts. Others search for peculiar types of terrain. The project is appropriately called "Clickworkers", because it involves much computer mouse clicking.
Mars Global Surveyor (MGS) arrived at the red planet five years ago and has sent home over 25,000 high-resolution images. Such volumes tend to overwhelm the small research teams directly in line. Alternatively, there are many people who lack scientific training but are enthusiastic about being involved in exploring Mars. A home computer, internet access, and considerable patience are all that is needed.
Inspiration here comes from the various downloadable "screensaver" programs that a computer can run to crunch data when it would otherwise be idle. The original of such screensavers is SETI@home ( setiathome. ssl.berkeley.edu ). Raw data collected using radio telescopes are grabbed by participants, and automatically scoured by their computers for signs of structured transmissions from extraterrestrial beings. SETI@home has just achieved the landmark of 4 million users. As of yet, no positive result has been found, otherwise you would have heard about it.
Others may prefer to be involved in cancer research, another area where distributed number-crunching is invaluable. Take a look at www.parabon.com to see how you can help. A wide variety of other projects, mostly of a scientific nature, are described on sites such as www. entropia.com and www.distributed.net.
The Clickworkers study takes this a step further. With a screensaver/distributed computing project all that is involved is an occasional download of a set of data, and the software to crunch the numbers. Very little user involvement is necessary. With Clickworkers, direct participation is the fundamental key: those choosing to participate accomplish tasks that scientists have so far been unable to program computers to do automatically. Our phenomenal eye-brain combination is the only solution.
One of these is impact crater recognition and classification. Clickworkers download Mars images obtained by the ongoing MGS project. They click on each crater, measure its size, and classify it as being fresh, degraded, or a "ghost" (a heavily eroded or overlain crater, which must therefore be old).
Such results enable the creation of a map of Mars in terms of ages for different regions of its surface. On Earth, impact craters are quickly (within thousands to millions of years) eroded by wind, rain, snow, volcanoes and earthquakes. We live on a very active planet, limiting crater lifetimes. By contrast, the Moon is dead, and craters there disappear only when a fresh impact occurs and eradicates some older ones.
Mars lies between these extremes. Its atmosphere is not as dense as our own, but phenomenal dust storms do happen. In the past, massive volcanic eruptions have occurred: Mars has the tallest volcano in the solar system, three times the height of Mount Everest. And although there is comparatively little water on Mars, it is clear that vast floods have inundated the surface.
Plains swept by floods have their craters either flattened or submerged by sediments, and so only recent impacts remain there now. Ancient upland regions maintain their pockmarks through the aeons, though. Thus a comparative dating of martian terrain is possible through the counting and classification of the hundreds of thousands of craters spread across it.
An obvious feature of Mars is that its southern hemisphere is much more densely cratered, and therefore older, than the north. Similarly the area around the prominent group of four large volcanoes on Mars is found to be virtually the youngest on the planet.
Some tens of thousands of volunteers have so far participated in the Clickworkers scheme. Many have just given it a quick look, and then got bored. Others have spent many hours poring over detailed pictures. The experience acquired by the latter group means their assessments improve as time goes by. By having several participants examine each image independently, the reliability and quality of the results can be diagnosed. During 2001, over 2 million distinct crater entries were archived in the Clickworkers project.
Asked her view of the success of Clickworkers so far, cratering expert Dr Nadine Barlow of Northern Arizona University, one of the project's organisers, replied that they had been "overwhelmed by the level of interest and excitement displayed by the public _ this is strong testimony to the desire of people to contribute to our understanding of the universe around us."
Apart from crater classifying, volunteers may also help in the search for unusual features on Mars. In particular, Nasa geologist Jeff Moore has suggested that a peculiar landform termed "honeycomb", found so far in just one place, may be evidence of the melting of huge ice blocks derived from glaciers that disappeared a long time ago. Clickworkers have turned their eyes to the rest of the planet, looking for the same type of structure, but without success so far.
Looking to the future, another major crater-counting effort is anticipated for a few years' time when Nasa's Dawn mission flies. This will visit the largest asteroid in the main belt, the 600-mile wide Ceres, and another of the biggies, Vesta. Crater numbers again will quantify the ages of their surfaces.
Interesting times ahead, for those who would like to be directly involved in our exploration of the solar system, and have a computer plus some time to burn. Joe Wise, director of the center for effective learning in Santa Monica, draws a parallel with the early exploration of the American north-west: "The Dawn team is following in the footsteps of Lewis and Clark, only using robotics for this exploration. In centuries past, the public was involved in exploration through accounts in newspapers and public lectures. But today's technology enables them to follow along with the explorers, piping the images into their homes. Clickworkers carries public involvement one step further. It allows the public to participate."
· Duncan Steel teaches space technology at the University of Salford.
