Linking the evolution of planetary surfaces with their atmospheres - Mars and beyond

Penny King, Professor, Australian National University

There are many outstanding questions about the evolution of the surface and atmosphere on the inner planets. Why is Earth a water world and how did its early surface interact with the atmosphere? How and why did Mars lose most of its H2O? Why is the martian surface covered in uniform dust with abundant iron oxides, sulfur and chlorine salts, and rare carbonate minerals? Why does Venus have a thick atmosphere? Why does Mercury have no atmosphere and putative reduced minerals?

In this talk, I will examine the hypothesis that high temperature reactions between gases and surface materials, early in the history of these planets, provide a framework to explain the planet’s broad surface and atmospheric features.

Hot gas-solid reactions are common on Earth and occur at volcanoes today. Our group has documented these reactions in the 2018 ash eruptions at Kilauea volcano and in the sub-surface of volcanoes. The reaction products are consistent with the results of our recent experiments and thermochemical models showing that hot gases react rapidly and efficiently with common silicate minerals and glasses to produce predictable products. These reactions occur over both temporal and lateral scales that demonstrably influence the evolution of a planet.

Since Mars has the oldest and best exposed crust, it provides a helpful analogue for the early inner planets.

Our experiments and models show that Mars’s surface and atmospheric evolution could occur via basaltic volcanism, impacts (including impacts into ice) and sedimentary processes; rather than catastrophic climate change inducing water-loss. We suggest that gas-solid reactions significantly contributed to the atmospheres of the inner planets by effectively “scrubbing” the reactive gases out of the early martian atmosphere leaving behind carbon dioxide gas, iron oxides, sulfur- and chlorine- minerals and rare carbonates.

This framework for Mars can be extrapolated to explain the surface and atmospheric evolution on the terrestrial planets. The differences between the planets today largely depend on the planet’s size and heliocentric distance which controlled the extent of surface-atmosphere-ice reactions.

Host: Mike Krawczynski

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