Finding an Alien Biosphere with Computational Chemistry

Clara Sousa-Silva
Thursday, December 2, 2021 · 4:00 pm
ESB 5104-06
Hosted by
Mark Jellinek

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At the edge of our present scientific frontier lies the question: “Can we identify the signs of life on an exoplanet?”. Establishing whether a planet is habitable, or inhabited, relies both on the observation of an exoplanet atmosphere and, crucially, its subsequent interpretation. This interpretation requires knowledge of the spectral behavior of every significant atmospheric molecule. However, though thousands of molecular candidates can contribute towards the spectrum of an atmosphere, data exist for only a few hundred gases. Among these, only a fraction have complete spectra (e.g. ammonia, water). This deep incompleteness in the knowledge of molecular spectra presents a pressing vulnerability in the atmospheric study of planets; there exists a strong possibility of mis-assignment, false positives, and false negatives in the detection of molecules.

The work presented in this talk combines structural organic chemistry and quantum mechanics to obtain the necessary tools for the interpretation of astrophysical spectra and, ultimately, the detection of life on an exoplanet. Whether alien life will produce familiar gases (e.g., oxygen) or exotic biosignatures (e.g., phosphine), painting a confident picture of a potential biosphere will require a holistic interpretation of an atmosphere and its molecules. In this talk Clara will describe ongoing efforts to train the next generation of scientists to decipher exoplanet atmospheres, and ultimately to detect a biosphere through the identification of volatile molecules, in particular those that might be produced by non-Earth-like life.


Speaker's Bio: 
Clara Sousa-Silva is a quantum astrochemist at the Center for Astrophysics | Harvard & Smithsonian. She investigates how molecules interact with light so that they can be detected on faraway worlds. Clara spends most of her time studying molecules that life can produce so that, one day, she can detect an alien biosphere. Her favorite molecular biosignature is phosphine: a terrifying gas associated with mostly unpleasant life. When she is not deciphering exoplanet atmospheres, Clara works hard to persuade the next generation of scientists to become an active part of the astronomical community.


Clara holds a doctoral degree in quantum chemistry from the University College London, and a masters degree in physics and astronomy from the University of Edinburgh in Scotland. Among her many achievements, Clara is the recipient of the prestigious 51 b Pegasi Fellowship from the Heising Simons Foundation. The fellowship supports the growing field of planetary astronomy and exceptional postdoctoral scientists who make unique contributions to the field of astronomy. Clara’s work and commentary has been featured in the BBC, WIRED, and the New York Times, among many others. Prior to joining the Center for Astrophysics, Clara served as a research scientist at MIT.