Abstract:
Understanding how the simple molecules present on the early Earth and possibly Mars may have set a path for complex biological molecules,
the building blocks of life, represents one of greatest unsolved questions. In this presentation, I discuss the effects of the solar/stellar forcing in its early history on the dynamics and chemistry of early Earth, Mars and exoplanets. I and my team at NASA/GSF perform numerical models of the effects of superflares, coronal mass ejection (CME) and solar energetic particle (SEP) events on the early Earth's atmosphere. Specifically, we modeled the effects of X-ray and UV emission (XUV) on the atmospheric loss from the early Earth and Mars. We also study propagation of frequent and energetic CMEs on early Earth magnetosphere and associated chemical impacts on its atmosphere due to energetic protons accelerated in shock waves driven by CMEs. The interaction of magnetic clouds ejected from the young Sun with magnetospheres of the early Earth causes significant perturbations of geomagnetic fields, which produce extended polar caps. These polar caps provide pathways for energetic!
particles associated with magnetic clouds to penetrate into the nitrogen-rich weakly reducing atmosphere and initiate the reactive chemistry by breaking molecular nitrogen, carbon dioxide, methane and producing nitrous oxide, the potent greenhouse gas, and hydrogen cyanide, the essential compound for life. This picture challenges the current models of warming of early Earth and Mars, by major atmospheric constituents, because CO2 and CH4 are destroyed due to collisional dissociation with energetic particles. Instead, we predict efficient formation of nitrous oxide as a by-product of these processes. This mechanism can consistently explain the Faint Young Sun's paradox for the early atmospheres of Earth and Mars. Our new model provides insight into how life may have initiated on Earth and Mars and suggests an alternative for the Habitability Zone in terms of the Biogenic Zone. It also predicts the spectral signatures of prebiotic molecules in atmospheres of planets "pregnant" with the potential for life.