Stronger Greenhouse Effect on Early Mars: Collision-Induced Absorption
by CO2-H2 and CO2-CH4 Complexes
Abstract
An unanswered question in planetary science is how could the early
Martian atmosphere have maintained a greenhouse effect sufficient to
allow for liquid water on the surface? A recent study by Wordsworth et
al. (DOI:10.1002/2016GL071766) suggested that previously unaccounted-for
collision-induced absorption (CIA) by carbon dioxide (CO2) and hydrogen
gas (H2), and by CO2 and methane (CH4) could provide the additional
atmospheric absorption needed to trap enough radiation to raise the
Martian surface temperature above freezing. However, as CIA
cross-sections for CO2-H2 and CO2-CH4 complexes do not exist in the
literature, the authors could only use computational methods to simulate
the CIA absorption cross-sections that they themselves identify in the
study as needing experimental validation. Preliminary results will be
presented from experimental measurements of the CIA cross-sections for
CO2-H2 and CO2-CH4 complexes performed using Fourier Transform
Spectroscopy. We have obtained Beam-time at the Canadian Light Source
Far-IR beamline in late October and early November which will allow us
to derive Cross-sections over a spectral range of 0-3000 cm-1 and a
temperature range of 200-350 K. In addition to allowing us to
experimentally validate the hypothesis of Wordsworth, the cross-sections
so obtained can also be applied to other planetary systems with CO2-rich
atmospheres, such as Venus, and will be useful to terrestrial
spectroscopists.