NASA Announces Intent to Fund Researchers to Study Stardust Samples

FAYETTEVILLE, Ark. — University of Arkansas researchers are receiving a grant to examine material from a comet sample brought back to Earth from outer space. They will try to determine its composition and age. This work will provide new insights into the formation and history of comets.

Fatemeh Sedaghatpour and Jonathan Craig, graduate students in the Arkansas Center for Space and Planetary Sciences, have received a three-year, $421,091 grant from NASA to perform thermoluminescence studies on samples returned from the Stardust mission in 2006. Using thermoluminescence, they will measure the light produced by heating samples, which provides information on the age and composition of the particles.

The technique, often used to date antiquities, was developed for use on extraterrestrial materials by Derek Sears, the W.M. Keck Professor of Space and Planetary Sciences and director of the space center. For many years, Sears used thermoluminescence to characterize meteorites found by scientific expeditions in the Antarctic.

“This technique can tell you things that no other geochemical or petrographical test can tell you,” Craig said. The grant will cover the construction of a clean room, micro-handling tools and stereoscopic scopes to help with the mounting and monitoring of samples during the thermoluminescence process.

To secure the grant, the researchers had to demonstrate that they could work with extremely small particles — as small as 10 to 100 micrometers, invisible to the naked eye. The meteorites and lunar material Sears worked with typically weighed in at the milligram scale. Sedaghatpour studied a series of micrometeorites, and Craig examined bits of a crushed meteorite matrix using the thermoluminescence technique.

“We were able to demonstrate that we could get a signal for particles that small,” Craig said.

As the sample is heated from room temperature up to about 500 degrees Celsius, both the temperature and light signal are recorded.

“Different minerals have different peak temperatures. That is why we can learn information about their crystalline structure, metamorphic history and mineralogy,” Sedaghatpour said.

The researchers will look at two different types of thermoluminescence — natural and induced. Natural thermoluminescence is produced from a sample in its “as received” state and provides information on the radiation exposure age of the material, or “how long it has been floating around out there,” Craig said. Induced thermoluminescence is produced by a sample drained of its natural thermoluminescence by momentarily heating the sample to a high temperature, then exposing it to a known radiation source. The information gleaned from this technique includes the history of heating, cooling and crystallization of the material in the sample.

After the thermoluminescence studies, the researchers will transfer the particles to a scanning electron microscope, which provides a high-magnification image of the material. They also use an energy dispersive X-ray device attached to the microscope that allows them to proportionally determine the percentages of the chemical elements present in the sample.

“The proposed measurements will help extract the maximum scientific information from Stardust particles and complement mineralogical, elemental and isotopic measurements, and they can be applied to large numbers of grains to 'map’ the history of cometary particles,” Sears said. “These studies address NASA’s objective of understanding small bodies as building blocks of the planets.”

The space center includes faculty and students from the J. William Fulbright College of Arts and Sciences and from the College of Engineering. Please visit http://spacecenter.uark.edu/ to learn more.