Researchers (shown left to right) Sean Brennan (MRUS), Konstantin Ignatyev (MRUS), Hope Ishii (LLNL) and Katharina Luening (MRUS).
(Photo by Diana Rogers)

Very early on Sunday, January 15, a NASA space craft thumped down onto the Utah desert. The Stardust probe had traveled halfway across the solar system to catch material from the tail of the comet Wild 2.

Soon, some of those particles will make a much shorter journey to California. When they arrive, a BayPac consortium composed of SLAC, UC Berkeley and LLNL scientists will be among the first to examine pristine comet particles.

“The sample return capsule is in spectacularly good shape,” SSRL physicist Sean Brennan said. “There will be hundreds of particles that can be analyzed.”

One of the main goals of the probe is to collect the raw elements that created the solar system about four billion years ago. These elements occasionally make it to earth on their own in the form of meteorites. But, according to Brennan, meteorites are “cooked fairly well on their way in,” burning up almost all elements besides iron and nickel. Brennan expects to see more volatile elements such as sulfur, selenium and phosphorus in the Stardust sample because the probe shielded these elements on their way through the earth’s abrasive atmosphere.

The SLAC team will focus on inorganic minerals. On Earth, these minerals have cycled through so many natural processes that they look vastly different than they would have at the beginning of the solar system. Wild 2 offers a special opportunity to sample a relatively unaltered comet because it existed on the edges of our solar system for billions of years before approaching the sun for the first time just 35 years ago. Relatively uncontaminated by processes within the solar system, Wild 2 most resembles the primordial components of the sun and its planets.

This photo shows particles traveling through Aerogel. By exposing the Aerogel to x-rays at SSRL, scientists will be able to identify the elements that make up the comet Wild 2’s tail.
(Photo courtesy of NASA)

Brennan and the BayPac team are part of an international preliminary examination collaboration examining a subset of the 130 Aerogel tiles that collected particles from the comet’s tail. Aerogel is an ultra-light material able to catch dust particles like sponge cake in a sandstorm. However, while granules in a sandstorm whip around at 60 to 100 miles per hour, the comet dust hit the Aerogel at about six kilometers per second (approximately 14,000 miles per hour).

Brennan and research partners Konstantin Ignatyev, Hope Ishii and Katharina Luening will expose the Aerogel to x-rays from SSRL. By comparing the wavelength of incoming rays to those exiting the sample, the researchers will identify the elements in Wild 2’s tail.

SSRL will have two chances to examine the comet dust with the synchrotron before the end of the year. Brennan and his team will also identify the most interesting samples and pass these along to LLNL, where researchers will slice off slivers 30 nanometers thick to analyze in their transmission electron microscope.

“All reports are that it is an extremely successful mission with years of research ahead of us. Very exciting,” Brennan said.