Research

Current Work

My work focuses on understanding how the planetary environment helps or hinders the emergence of life.  A major research focus is the ultraviolet (UV) radiation environment on planetary surfaces. While UV light is a stressor for extant life, theoretical, empirical, and laboratory studies suggest that midrange UV light (200-300 nm) may have played a role in the synthesis of molecules relevant to the origin of life, and in particular RNA. I showed that the existing UV sources that were used to study the origin of life were poor approximations to natural UV 3.9 billion years ago. I placed robust constraints on the UV environment on early Earth. I compared this UV to that available on early Mars, and concluded that early Mars UV was probably similar to early Earth UV. On the other hand, I showed that planets orbiting red dwarf stars (the most common type of star in the galaxy and the first exoplanets we will be able to search for evidence of life) have UV-poor surfaces, and that UV-dependent prebiotic chemistry might not proceed on them. My work has prompted a series of laboratory studies, to understand whether pathways that work in the lab could have worked on early Earth, and whether those that worked on early Earth could have worked on other worlds as well.

I have constrained other aspects of the prebiotic environment. I demonstrated that shallow lakes on early earth were likely rich in sulfite. Experimental follow-up studies demonstrated that sulfite can aid in the synthesis of ribonucleotides, the monomers of RNA. Sulfites also eliminate the need for copper in such chemistry in favor of iron. Since iron is much more common than copper on the terrestrial surface, this makes it much more plausible that this chemical pathway could have occured on early Earth and hence is relevant to the origin of life. Other work argues that nitrate should have also been abundant in shallow lakes on early Earth but not in the ocean, with implications for proposed origin-of-life scenarios.

A new area of work for me is in planetary atmospheres. I am working to rewrite a photochemistry code, and to use it to study the evolution of rocky planet atmospheres and potential biosignature gases of life in such atmospheres.

My overall goals are 1) to improve the realism of  laboratory studies of the origin of life on Earth, and 2) to understand how different planets compare as venues for life to form, in this solar system and beyond. 

The code associated with my papers is available on GitHub, unless forbidden by legal or collaboration rules.

Past Work

My early work in graduate school focused on using the Wide-Field Camera 3 instrument on the Hubble space telescope to study the atmospheres of 5 hot Jupiter exoplanets. My work constrained the abundance of water on these worlds, and helped demonstrate the robustness of WFC3 for transmission spectroscopy. 

As part of the 2010 NASA Academy at Ames Research Center, I worked with Dr. Nathalie Cabrol on finding and characterizing terrestrial Mars analog environments under stress due to climate change.  Also as part of the Academy, I proposed and lead the science team on Project LAMBDA, which explored a novel method of detecting life based on microbial fuel cell (MFC) technology. I later participated in our expedition to the Mars Desert Research Station to further test LAMBDA. 

At MIT, I worked with Professor Sara Seager on modeling exoplanet atmospheres, studying the noise properties of CoRoT data, and on the design of ExoplanetSat, a satellite designed to find Earthlike planets in the habitable zones of bright nearby stars. 

At SRI International, I helped study the Earth’s ionosphere by developing analysis tools for the AMISR polar radar system.