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Conel M. O'D. Alexander

Conel Alexander


Among other affiliations, Conel Alexander is a member of the NASA Astrobiology Institute (NAI), an interdisciplinary research consortium made up of academic and nonprofit organizations and NASA centers. Astrobiology is the study of the origin, evolution, distribution, and future of life in the universe.

 

Chondrules

In his work on chondritic meteorites — the most primitive type of meteorites — Conel Alexander analyzes chondrules. Chondrules, the tiny, millimeter-size spheres that are the dominant constituent of chondritic meteorites, are seen here at varying magnifications.

Some 40 thousand tons of extraterrestrial material fall on Earth every year. This cosmic debris provides cosmochemist Conel Alexander with information about the formation of the solar system, the galaxy, and perhaps the origin of life.

Alexander studies meteorites to find the clues they provide to discern what went on before and during the formation of our solar system. Meteorites are fragments of asteroids - small bodies that originated between Mars and Jupiter and are likely the last remnants of objects that gave rise to the terrestrial planets He is particularly interested in the analysis of chondrules, millimeter-size spherical objects that are the dominant constituent of the most primitive types of meteorites. Chondrules formed as molten droplets prior to the formation of the asteroids. Alexander develops techniques to measure precisely the isotopic species of the elements potassium, iron, magnesium, and oxygen in meteorite samples. Depending on the conditions, these elements may have evaporated and recondensed during chondrule formation. The isotopic compositions can indicate the extent of evaporation and recondensation, which can reveal the conditions present when chondrules formed.

Alexander's other major interest is presolar materials preserved in meteorites. These include the tiny grains that emerged around dying stars and interstellar organic matter. By deciphering these relics, he hopes to understand the processes of galaxy evolution, the formation of the elements inside stars via nucleosynthesis, and stellar evolution.

In recent years, evidence has mounted that meteorites may have played a role in the origin of life on Earth. Alexander studies this possibility as part of his work on the origin of interstellar organic matter in meteorites. Analysis has shown that meteorites contain more than 70 amino acids and three of the nucleic acids in RNA and DNA — the molecules that are essential to life. Many amino acids are chiral molecules, meaning that they come in two mirror-image forms - left-handed and right-handed. It is the left-handed forms that are almost exclusively present in living organisms and that are, in some instances, slightly more abundant in meteorites. With these objects constantly bombarding the Earth, it is possible that they ferried the precursors of life to this planet and that they played a role in the emergence of life elsewhere.

A small number of meteorites come from Mars. They have a wide age range and contain water-bearing minerals. By studying the hydrogen isotopes of this water, Alexander hopes to test ideas about what happened to the water that was originally on the planet.

SELECTED PUBLICATIONS

  • Alexander, C. M. O'D. 2002. Application of MELTS to kinetic evaporation models of FeO-bearing silicate melts, Meteoritics Planet. Sci. 37, 245-256.

  • Alexander, C. M. O'D., S. Taylor, J. S. Delaney, P. Ma, and G. F. Herzog. 2002. Mass-dependent fractionation of Mg, Si, and Fe isotopes in five stony cosmic spherules, Geochim. Cosmochim. Acta 66, 173-183.

  • Grossman, J. N., C. M. O'D. Alexander, J. Wang, and A. J. Brearley. 2002. Zoned chondrules in Semarkona: evidence for high- and low-temperature processing, Meteoritics Planet. Sci. 37, 49-73.

  • Alexander, C. M. O'D., A. P. Boss, and R. W. Carlson. 2001. The early evolution of the inner solar system: a meteoritic perspective, Science 293, 64-68.

  • Krot, A. N., A. Meibom, S. S. Russell, C. M. O'D. Alexander, T. E. Jeffries, and K. Keil. 2001. A new astrophysical setting for chondrule formation, Science 291, 1776-1779.

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