Paul Carroll, Ph.D.

Education: California Institute of Technology, Ph.D., Chemistry
Institution: Smithsonian Astrophysical Observatory (laboratory of Michael McCarthy)

SCOL Project: Exploring the Cosmic Origins of Chiral Molecules

One of the most fundamental and fascinating questions of modern science is: How did life begin on Earth? In the course of studying the fundamental workings of biological systems, scientists noted an asymmetry in the way life employs handed molecules; that is, molecules whose mirror image is not the same as the original. These molecules, referred to as chiral, are integral to biology. This asymmetry, termed homochirality, is the biological use of only one of the possible mirror images, or enantiomers. Employing only one enantiomer affords numerous evolutionary advantages, and is found in every living thing. This asymmetry is the same across the biosphere, that is, all living things not only employ only one enantiomer of many molecules, they employ the same enantiomer. One of the great mysteries of homochirality is that enantiomers are virtually identical, having the same physical properties. This raises the question: How did life choose the handedness it did when faced with seemingly identical choices? Many processes have been proposed that could generate a small asymmetry, or excess, in enantiomers on the early Earth that drove homochirality. The possibility that interests me, and that is the central topic of my proposal, is that the primordial material from which Earth was assembled contained chiral molecules with this small enantiomeric excess.

It has been shown that meteorites contain amino acids, the building blocks of proteins, which contain a small enantiomeric excess and are therefore a plausible origin for homochirality. As an astrochemist, I am interested in how this enantiomeric excess came to be. Using radio astronomy, I study the molecular content of star-forming regions, the nurseries from which solar systems are born. The goal of my research is to characterize where and how the organic material in these regions comes to be, and how it becomes part of the solar systems that form from it.

Recently, I detected the first chiral molecule outside our solar system, propylene oxide. This molecule at last provides a target we can study to learn how chiral molecules may form and what astrophysical processes may create enantiomeric excess. My research as a SCOL postdoctoral fellow will build the foundation necessary to carry out these studies through two projects. First, studying enantiomeric excess requires a type of observation never before conducted. A first step in planning such observations is demonstrating they are feasible in the lab. Accomplishing this will be a major goal of my work. Second, we have only recently detected propylene oxide and still know very little about its origins. As part of my research I will use astronomical observations to better understand where and how propylene oxide forms. Together, these projects will greatly enhance our understanding of chiral molecules in the universe and shed light on one of the major questions in the study of the origins of life.