2015 Annual Science Report
VPL at University of Washington Reporting | JAN 2015 – DEC 2015
Planetary Surface and Interior Models and SuperEarths
We use computational and theoretical models to simulate the evolution of the interior and the surface of real and hypothetical planets around other stars. Our goal is to determine the characteristics that 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.
Planetary Interior Models and the Evolution of Terrestrial Planets: Driscoll and Barnes (2015) coupled a 1-D Earth-like planet interior model for thermal/magnetic/volcanic evolution to standard models of tidal processes to produce the first self-consistent geophysical model for thermal-orbital planetary evolution. Their simulations showed that, contrary to prevailing opinions, Earth-like planets orbiting red dwarfs are likely to maintain strong magnetic fields that would shield the planet from the host star’s activity. They also found that terrestrial planets in the habitable zone around low mass stars experience significant tidal heating that can make the surface uninhabitable and prevent magnetic field generation, making the surface vulnerable to high energy radiation.
Zahnle, Sleep and colleagues showed that thermal blanketing by Earth’s water atmosphere limits the rate the Moon’s orbit can evolve in the first ten million years after the Moon-forming impact. This work provided the first good estimates of how quickly the surface of the Earth can freeze after the Moon-forming impact and calculated the geothermal heat flow for the first hundred million years of the Hadean (Zahnle et al. 2015).
Sleep also published a review of the tectonic history of the Earth including a discussion of the conditions for the origin and evolution of early life on Earth, the biological effects on global geological processes, and other concepts of high relevance to astrobiology (Sleep, 2015a). Sleep also examined the similarities and differences between tidally-induced cracks on Enceladus and the San Andreas fault, which can be used to infer processes on tidally evolving exoplanets (Sleep, 2015b).
Sleep has also been working on the source for the Pt-rich veneer component in the Earth’s mantle and in the moon, considering whether the Pt-rich veneer in the Earth’s mantle came from Theia’s (the object that hit the Earth to form the Moon) core or later asteroids.
Weathering Models: Bolton continued to use and develop a reactive transport model to simulate weathering at planetary surfaces. He continued production runs to quantify CO2 drawdown from the atmosphere by weathering of soils derived from idealized granite and basalt rock types, examining the influence of changes of the mineralogic and rainwater compositions that can have a profound impact on solution pH and weathering rates. This modeling is being done to find the influence of atmospheric composition, temperature, and infiltration rates on weathering related CO2 consumption (an important factor in the global carbon cycle). A vadose zone model is being further tested and refined. A collaboration exploring the influence of heterogeneous permeability on effective kinetic rates in 2D soils continued to help resolve the so-called lab/field rate conundrum.
VPL Team Member Bolton also examined pyrite and organic matter (OM) oxidation rates in eroding shales under atmospheres with 0.1% to 18% of the present atmospheric level of oxygen in a collaboration with Noah Planavsky and Chris Reinhard (of the NAI Alternative Earths team based at UC Riverside, lead PI: Timothy Lyons) in order to elucidate changes in the global carbon cycle during the rise in atmospheric oxygen in Earth.
PROJECT INVESTIGATORS:Edward Bolton
Project InvestigatorPeter Driscoll
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