The Meteoritical Society recently created the Nier Prize for scientists under the age of 35 who have “made a significant contribution in the field of meteorites and closely allied fields of research.” Larry Nittler received the award in 2001.

The best-investigated presolar grains are the silicon carbide (SiC) type (above). They typically range in size from 1 to 20 millionths of a meter (micron). This one, from the Murchison meteorite, is about 2 microns across. The isotopic signatures of this type of grain suggest an origin in old red giant stars and supernova explosions.

Cosmochemist Larry Nittler studies extraterrestrial materials, including meteorites and interplanetary dust particles (IDPs), to understand the formation of the solar system, the galaxy, and the universe and to identify the materials involved. He is particularly interested in developing new techniques to analyze different atomic species, or isotopes, in small samples. In related studies, he uses space-based X-ray and gamma-ray spectrometers to determine the composition of planetary surfaces, and he was part of the 2000-2001 scientific team to hunt for meteorites in Antarctica.

Nittler is especially interested in presolar grains contained in meteorites and in what they can tell us about our cosmic origins. He develops and uses advanced microanalytical techniques to locate and analyze these particles. The solar system formed about 4.5 billion years ago from a cloud of gas and dust. Most of the original dust grains were vaporized during solar system formation, but in the 1980s, researchers discovered that a fraction of these particles survived, trapped in mete-orites. Presolar grains are tiny—about one thousandth of a millimeter in diameter. They predate other solid material in the solar system and are believed to have formed in winds and explosions of ancient dying stars. The unusual abundance ratios of different isotopes in presolar grains compared with other solar system products are their defining feature. They give researchers information about a number of processes, including how elements are synthesized inside stars, how the Milky Way galaxy evolves, and what the first solar system materials were.

Nittler recently worked on NASA’s Near Earth Asteroid Rendezvous (NEAR) mission to advance our understanding of the relationship of asteroids to meteorites. Although it is known from both calculations and observations that most meteorites originated from asteroids, it has been difficult to link specific asteroid classes to specific meteorite classes. NEAR orbited the 30-km-diameter asteroid Eros for a period of one year during 2000 and 2001. Nittler, with collaborators, reduced and interpreted data from the X- ay spectrometer aboard NEAR to determine the elemental composition of the asteroid’s surface. The data clearly showed that Eros is primitive; it has not differentiated into a core, mantle, and crust. Except for the ratio of sulfur to silicon, the elemental ratios agree with those measured in ordinary chondrites—the most common type of meteorite—indicating a possible relationship. The sulfur/silicon ratio, however, is much lower than in chondrites, a fact that most likely reflects some sort of “space-weathering” processes causing sulfur to volatilize and escape. Nittler continues to explore this and related questions in his research.

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