New Molecular Discovery

Learning anything about our cosmic chemical heritage first requires that we understand the molecules that are present in any given environment in space. We are first and foremost a molecule hunters, using the spectra measured here on Earth to detect these species in the interstellar medium (ISM). The associated figure is a Rogue's Gallery of some of the molecules we have identified in space for the first time. Of particular note here are propylene oxide (the first chiral molecule ever detected in space) and the aromatic species, the detections of which are opening a new sub-field of astrochemistry. We are exploring this new, unexpected aromatic chemistry, how it interacts with what we believe we already know about the evolution of prebiotic chemistry in the ISM, and how it changes what we think we know about the formation of stars and planets.

Chemistry in Dark Molecular Clouds

Dark molecular clouds like the one shown here are the places where gas and dust will eventually begin collapsing to form new born stars. Because the clouds are dense (relatively speaking), the interiors are shielded from harsh interstellar radiation, and complex chemistry can begin to occur. This happens both in the gas-phase (where we can most easily detect) and monitor its progress via rotational spectroscopy, and on the surfaces of interstellar dust grains coated in ice.

For quite some time, we have believed this chemistry to be relatively limited. Exotic species, largely formed through low-energy gas-phase reactions between ions and radicals, could certainly occur. But otherwise, it was not though that highly complex molecules would be present in substantial quantities until a star turned on and injected heat and energy into the system to drive more complex chemistry. Our detection of benzonitrile in one of these clouds (TMC-1; McGuire et al. 2018 Science 359, 202) suggested this may have been a poor assumption. Our group is now testing the limits of molecular complexity in TMC-1 and sources like it, trying to understand exactly how complex the chemistry can evolve in the absence of a star.

Photograph of the Taurus Molecular Cloud complex taken by McGuire from Charlottesville, VA. The dark lanes in the top of the image aren't regions without stars - they are deeply obscured clouds of gas and dust that block out all starlight from behind them.

Chemistry in Star-Forming Regions

Once a star turns on, the radiation that it emits begins to raise the temperature of the ices covering dust grains. This enables small molecules (neutrals, radicals) to roam the surface and react with other species, building up more complex molecules. Many of these look more like what is seen terrestrially: methane, methanol, ethanol, and perhaps even things as complex as amino acids. As the star warms up, these molecules are released into the gas-phase where they undergo more reactions and we can again detect and monitor them. At some point, these inventories are incorporated into form planetary systems: comets, asteroids, and planets. How much of the chemistry from the dark cloud and star-forming phase is preserved and transported to planets? How much is destroyed? How does the chemistry in these environments imprint itself upon the chemistry of life that arises on those planets?

Photograph of the Galactic Center taken by McGuire from the summit of Mauna Kea. Very near the central supermassive black hole Sgr A^* is a massive star-forming region called Sgr B2. It is here that a huge fraction of the new complex organic molecules are discovered outside our solar system.