For more than 20 years, NASA has flown high-altitude research aircraft to collect cosmic dust -- debris of comets and asteroids that fills the inner solar system. In late April though, they made the first attempt to collect dust particles from a very specific target -- comet Grigg-Skjellerup.

Until that flight, scientists had no way of knowing the cosmic origin of the dust particles they collected. Using a computer model developed by Dr. Scott Messenger, a researcher in the Office of Astromaterials Research and Exploration Science at NASA's Johnson Space Center in Houston, they were able to determine exactly when to fly in order to catch a piece of the comet they wanted to examine.

"In effect, NASA is exploring the solar system with airplanes," Messenger said.

Messenger predicted that the week of April 22 was the best opportunity for collecting Grigg-Skjellerup particles, as the Earth passed through the dust stream created by the comet as it flew around the Sun.

Dust streams from comets are similar to those that produce meteor showers, but are different in several important ways. First, the particles are much smaller than meteor particles, which are about the size of a grain of sand. Second, the dust streams hit the Earth's atmosphere at much lower speeds, enabling the dust to survive entry into the atmosphere without melting. Third, these streams are very young, produced as recently as 30 years ago, while many meteor streams are hundreds of years old.

This last aspect is what makes the comet dust particles possible to identify in the dust collections, even among a very abundant background of interplanetary dust. The fresher cometary dust particles can be identified by their lack of solar flare damage tracks and implanted gas from the solar wind. Dust particles from comet Grigg-Sjkellerup will be identified by a detailed examination of the collected samples, a process that could take years.

"The key measurements will be performed by transmission electron microscopy, a technique that gives compositional information on an atomic scale," Messenger said.

Comet samples are a good place to look for the ingredients of the early solar system, which themselves came from the remnants of early stars in the universe.

"Identifying cometary dust particles will allow us to study the most distant parts of the solar system on a microscopic scale," Messenger said.