Stardust in meteorites

Abstract

Primitive meteorites, interplanetary dust particles, and comets contain dust grains that formed around stars that lived their lives before the solar system formed. These remarkable objects have been intensively studied since their discovery a little over twenty years ago and they provide samples of other stars that can be studied in the laboratory in exquisite detail with modern analytical tools. The properties of stardust grains are used to constrain models of nucleosynthesis in red giant stars and supernovae, the dominant sources of dust grains that are recycled into the interstellar medium by stars.O ne of the great discoveries in cosmochemistry in the last century was the fact that primitive meteorites contain tiny mineral grains that condensed around dying stars. These grains survived a myriad of destructive environments, including the immediate surroundings of their parent stars, the interstellar medium, the molecular cloud that collapsed to form the solar system, the solar nebula, meteorite parent bodies, breakup of those bodies, and atmospheric entry. There were a number of hints of the presence of these grains over the years, mainly from strange isotopic patterns of the noble gases, and a nearly two-decade search for the hosts of the anomalous isotopic patterns culminated in the discovery of diamond (1), silicon carbide (2, 3), and graphite (4) in carbonaceous chondrites in the late 1980s. These grains are commonly referred to as "presolar grains," although the more evocative name "stardust" is often used. The latter term will be used here, because it is now clear that these grains formed around individual stars with little apparent subsequent modification in the interstellar medium. Note that the name is also used for the National Aeronautics and Space Administration (NASA)'s Stardust mission, which returned dust grains from Comet Wild 2 (surprisingly little actual stardust has been detected so far) and from the contemporary interstellar medium (not yet confirmed).The mineralogy, textures, chemistry, and isotopic composition of stardust from meteorites provide direct evidence of processes that occurred in individual stars and complement observations by more traditional astronomical methods. Stardust from meteorites samples a number of different types of stars, including asymptotic giant branch (AGB) stars, part of the normal stellar evolution of stars 1.5 to 4 times the Sun's mass, as well as core-collapse supernovae and novae. Diamond, silicon carbide, and graphite are common types of stardust but are thermodynamically unstable in the solar nebula, so their survival places constraints on physicochemical conditions in the solar nebula.Stardust grains are small: although the largest grains can reach a few tens of μm in diameter, such grains are very rare, and most grains are μm-sized or less. For this reason, laboratory study of stardust has driven advances in analytical technology and progress depends on further improvements in spatial resolution and analytical sensitivity.Here, we begin with a brief d...

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