Sukrit Ranjan, Ph.D.

Education: Harvard University, Ph.D., Astronomy & Astrophysics
Institution: Massachusetts Institute of Technology (laboratory of Sara Seager Group)

SCOL Project: The UV Ultraviolet Environment for the Origin and Evolution of Life

We are in the midst of two revolutions in our understanding of life and its origins (abiogenesis). The first revolution is chemical: Long-standing problems in chemistry relating to the origin of life (prebiotic chemistry) are rapidly being solved. In the RNA world hypothesis, an abiotic synthesis of RNA is the key step in the origin of life, and the first plausibly prebiotic syntheses of RNA are now being discovered. The second revolution is astronomical: Recent studies have shown that potentially habitable planets orbiting other stars (exoplanets) are common, and the next generation of telescopes will be able to search them for evidence of life.

Ultraviolet (UV) light plays a key role in both of these revolutions. UV photons have the energy to power molecular and atomic transitions. This means that UV light can both harm nascent life and power the synthesis of prebiotically important molecules (e.g. RNA). Whether and how UV light helps or impedes the origin of life depends on the nature of the UV light that penetrates the atmosphere and reaches the planet’s surface. Consequently, it is critical to characterize the surface UV environment for prebiotic chemistry.

I propose three investigations to constrain the surface UV environment and explore the implications for prebiotic chemistry. The first investigation focuses on the UV environments for planets with highly scattering atmospheres, due to either high surface pressures or thick clouds. The second investigation focuses on the potential for elevated rates of volcanic outgassing, of the kind suggested for the young Earth and young Mars, to suppress UV light at the surface. The third investigation focuses on the impact of stellar flares, which are more common and more energetic for younger stars, on the surface UV environment. These investigations have applications both within the solar system (e.g., for the young Earth and young Mars) and outside it (e.g., for exoplanets).

This work will help prebiotic chemists understand whether UV-sensitive prebiotic chemistry discovered in the lab could work in nature, and the environmental context in which abiogenesis occurred. It will help astronomers understand whether life can emerge and endure on planets orbiting active stars, like Proxima Centauri b, our recently discovered potentially habitable nearest neighbor. This work will constrain which kinds of planets are the friendliest for the emergence of life, and hence which ones are the best targets for telescopic searches for extraterrestrial life. These searches will start in earnest in 2018 with the launch of the James Webb Space Telescope.

My proposed work is a novel investigation of the possible UV environments on planetary surfaces, critical for understanding both prebiotic chemistry on Earth and the habitability of extrasolar planets. It synergizes strongly with existing SCOL research initiatives and with work being done at my proposed host institution.