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.