2012 Annual Science Report
VPL at University of Washington Reporting | SEP 2011 – AUG 2012
Planetary Surface and Interior Models and SuperEarths
We use computer models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to work out what sorts of initial characteristics are most likely to contribute to making a planet habitable in the long run. Observations in our own Solar System show us that water and other essential materials are continuously consumed via weathering (and other processes) and must be replenished from the planet’s interior via volcanic activity to maintain a biosphere. The surface models we are developing will be used to predict how gases and other materials will be trapped through weathering over time. Our interior models are designed to predict how much and what sort of materials will come to a planet’s surface through volcanic activity throughout its history.
Weathering Models: Bolton continued to extend and use a reactive transport model to simulate weathering at planetary surfaces. It is well known that weathering reactions of silicate and aluminosilicate minerals consume CO2, and thereby weathering can modify atmospheric compositions. We began production runs aimed at quantifying CO2 draw-down from the atmosphere by weathering of soils derived from idealized granite and basalt rock types. This modeling is being done to find the influence of atmospheric composition, temperature, and infiltration rates on weathering related CO2 consumption. Bolton has started a collaboration with UW student Wayne Stewart for his DDF Marker-Toolkit project focused on Martian weathering. Additional minerals needed for this project are being added to the database used by the weathering model KINFLOW. We have started the development of a graphical user interface (GUI) to simplify changing input files for the weathering model. Graphics using R were improved for data visualization. Boundary conditions for infiltration of fluid chemical solutes were augmented and tested.
Earth as a Test Case: Odgen and Sleep (2012) studied the effects of intrusion of flood basalts into thick coal bed with respect to the end-Permian extinction. Basalt mingles with coal forming a volatile-rich fluid with properties analogous to andesite. At a minimum, the process explains coal fly ash at the extinction horizon. Eruption of trillion tonne quantities of coal carbon would acidify the shallow layer of the ocean in a few years before it had time to mix. This process is an attractive explanation for the preferential extinction of shelly marine organisms and marine carbonate dissolution at the extinction boundary.
Super-Earths: Using surface gravity (rather than mass) as the scale for planetary size greatly aids in obtaining compact dimensional formalae relevant to silicate planets (Sleep 2012). By Gauss’ law, both surface gravity and surface heat flow depend on the ratio of surface area to planetary mass. The thermal gradient d(temperature)/d(pressure) then does not explicitly involve planetary size. The thickness of the lithosphere and the oceanic crust scale inversely with gravity. Surface gravity (in Earth g’s) does not vary much: from ~0.4 for Mars to ~3 for 10 Earth mass super-earth.
PROJECT INVESTIGATORS:Edward Bolton
Project InvestigatorNorman Sleep
PROJECT MEMBERS:Rory Barnes
RELATED OBJECTIVES:Objective 1.1
Formation and evolution of habitable planets.
Indirect and direct astronomical observations of extrasolar habitable planets.
Earth's early biosphere.
Co-evolution of microbial communities
Effects of environmental changes on microbial ecosystems