To insure that the volunteer scanners know what they're doing, each must pass a test where he or she is asked to find the track in a few test samples. To judge the reliability of each volunteer - and to provide some reward in what for most will be a fruitless search - the team also plans to throw in some ringers with and without tracks.
"We will throw in some calibration images that allow us to measure the volunteers' efficiency," Westphal said.
If at least two of the four volunteers viewing each image report a track, that image will be fed to 100 more volunteers for verification. If at least 20 of these report a track, UC Berkeley undergraduates who are expert at spotting dust grain tracks will confirm the identification. Eventually, the grain will be extracted for analysis. Discoverers will get to name their dust grains.
The dust grains were collected in two phases during the Stardust spacecraft's seven-year journey to and from Wild 2 as the spacecraft turned its Stardust Interstellar Dust Collector (SIDC) into the interstellar dust stream, which courses through the solar system at a speed of about 20 kilometers (12 miles) per second. The dust grains will have made carrot-shaped trails in the aerogel, which is a novel, silicon-based sponge 100 times lighter than water.
In the early morning hours of Jan. 15, 2006, the Stardust payload will parachute into Utah's Salt Lake Desert and be airlifted to Houston, where teams will open it so as to minimize contamination from other dust. When launched in 1999, NASA was unsure how to remove from the aerogel the micron-sized cometary grains and the nearly invisible interstellar dust grains.
"It's amazing that Stardust flew without anyone having a clue as to how to get particles out of the aerogel after it came back," Westphal said. "You have to give NASA credit for taking a risk."
During Stardust's quiet journey to a rendezvous with a comet, however, Westphal led a team that created tools for extracting both comet grains and interstellar dust grains. Working with Chris Keller, formerly at the Berkeley Sensor and Actuator Center and now at MEMS Precision Instruments, he developed microtweezers and what he calls micro-pickle forks to pull comet grains from the aerogel for detailed analysis of their elemental and isotopic composition. The abundances and composition within comet grains will tell scientists about the conditions in the early solar system.
These same techniques will be used to extract interstellar dust grains, but first they have to be found. Based on earlier work with glass cosmic-ray detectors on the Mir space station, Westphal developed an automated microscope to digitally photograph the entire area of the aerogel in patches - the size of a salt grain - that can be viewed later in search of dust particles. The lengthy but exciting search for dust grains will be conducted by Internet volunteers.
Once the grains are identified and analyzed, Westphal hopes the information will tell about the internal processes of distant stars such as supernovas, flaring red giants or neutron stars that produce interstellar dust and also generate the heavy elements like carbon, nitrogen and oxygen necessary for life.
The virtual microscope was developed by computer scientist David Anderson, director of the SETI@home project, along with physics graduate student Joshua Von Korff. Craig and Mendez are now creating a teacher's lesson guide that uses the Stardust@home Virtual Microscope to teach students about the origins of the solar system. A section of the Stardust@home Web site (http://stardustathome.ssl.berkeley.edu/) also will be aimed at the general public.