2013 Annual Science Report
VPL at University of Washington Reporting | SEP 2012 – AUG 2013
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: e.g., subduction, sediment burial) 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 and biological processes over time. Our interior models are designed to predict tidal effects, heat flow, and how much and what sort of materials will come to a planet’s surface through resurfacing and volcanic activity throughout its history.
In this task VPL team members look at internal and surface planetary processes and how these may impact habitability, and in turn be impacted by life.
Co-Evolution of the Environment with Life: Sleep and colleagues looked at the partitioning of radionuclides in the Earth’s mantle, crust and hydrosphere as the result of biologically mediated geochemical evolution (Sleep et al., 2013). Decay of radionuclides in Earth materials can emit an electron antineutrino (geoneutrinos) from U and Th series decay within the Earth. Secular variations in the distribution and abundance of the radionuclides U, Th and K within Earth’s mantle, crust, and hydrosphere have been strongly influenced by the geochemical evolution of life’s metabolic processes. This is because biological processes influence the redox state of U and Th, which in turn influences how these elements are partitioned between the crust and the mantle as moderated by subduction processes. Overall, geoneutrino data constrain the masses of mantle chemical and isotopic domains recognized by studies of mantle-derived rocks and show the extent of recycling into the mantle over geological time (Sleep et al., 2013). Sleep (2013, book chapter submitted) also discussed the last universal common ancestor (LUCA) and the initial Darwinian ancestor (IDA) related to genomics and nodes on the tree of life that can arise from true bottlenecks implied by the marine serpentinite origin scenario and by asteroid impact. Sleep et al., (2013, submitted) discuss the state of the mantle and crust soon after the moon-forming impact, the influence of lunar induced earth-tides on these zones, and the fate of CO2 in the mantle and atmosphere in the Hadean. Sleep and Lowe (2013, in preparation) examine the physics of crustal fracturing and dike formation triggered by large meteorite impact in the Barberton greenstone belt, South Africa.
Driscoll started as a VPL postdoctoral researcher in August this year and has since made
significant progress writing a numerical program to model the internal evolution of a rocky terrestrial planet. The model consists of a coupled thermal history of the mantle and core the includes radioactive heat generation, heat loss due to mantle melting, inner core growth, and magnetic field generation in the outer core. Next year additional heat sources such as tidal heating will be added, and the code will be coupled to the larger VPLANET exoplanet modeling code that simultaneously computes the orbital history of the planet. Driscoll also submitted a paper on the thermal history modeling applied to Earth and Venus. Work in progress includes a new solution to the “thermal catastrophe” and “new core paradox” problems in the thermal history of the Earth.
Weathering Models: Bolton used a reactive transport model to simulate weathering at planetary surfaces. Production runs aimed at quantifying CO2 drawdown from the atmosphere by weathering of soils derived from idealized granite and basalt rock types were continued. This modeling is being done to find the influence of atmospheric composition, temperature, and infiltration rates on weathering related CO2 consumption. A coupled model for aqueous and gaseous phase flows for vadose zone dynamics is being implemented. We are exploring the influence of heterogeneous permeability on effective kinetic rates in 2D soils. Some delay in advancing the production runs because the code runs too slowly. We are coding and testing a method for automatic adjustment of the length of the time step, which we hope will improve the code’s efficiency. We have implemented and tested a graphical user interface (GUI) to simplify changing input files for the weathering model.
PROJECT INVESTIGATORS:Edward Bolton
Project InvestigatorNorman Sleep
PROJECT MEMBERS:Peter Driscoll
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