2012 Annual Science Report

VPL at University of Washington Reporting  |  SEP 2011 – AUG 2012

Executive Summary

Overview

The Virtual Planetary Laboratory’s interdisciplinary research effort focuses on answering a single key question in astrobiology: If we were to find a terrestrial planet orbiting a distant star, how would we go about recognizing signs of habitability and life on that planet? This question is relevant to the search for life beyond our Solar System, as outlined in NASA’s Astrobiology Roadmap Goals 1 and 7. VPL research spans many of the Roadmap objectives, but is most relevant to Objectives 1.1 (Formation and Evolution of Habitable Planets), 1.2 (Indirect and Direct Observations of Extrasolar Habitable Planets) and 7.2 (Biosignatures to be Sought in Nearby Planetary Systems).

Recent observations have brought us much closer to identifying extrasolar environments that could support life. The successful Kepler Mission has found over two thousand planetary candidates – many of them smaller than twice the diameter ... Continue reading.

Field Sites
29 Institutions
14 Project Reports
78 Publications
4 Field Sites

Project Reports

  • 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.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • Understanding the Early Mars Environment

    There is no liquid water on modern Mars, although there is plenty of solid ice. Observations from orbiting satellites and rovers on the ground suggest that liquid water may have flowed over the Martian surface in the distant past. VPL researchers are studying the geologic record of Mars for clues of past water, and investigating climate and chemical conditions under which water would be stable. Team members examined different climate feedbacks and geochemical processes that could have warmed the early Mars. Some members are also active members of the MSL science team.

    ROADMAP OBJECTIVES: 1.1 2.1
  • Postdoctoral Fellow Report: Steven Mielke

    S. P. Mielke completed an NAI NASA Postdoctoral Program (NPP) fellowship during September 1, 2011 to February 29, 2012. His postdoctoral research has provided the basis for the project: “The Long-Wavelength Limit for Oxygenic Photosynthesis.” He continues this research as a Research Associate at Rockefeller University.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • The Long Wavelength Limit for Oxygenic Photosynthesis

    Photosynthesis produces signs of life (biosignatures) on a planetary scale: atmospheric oxygen and the reflectance signature of photosynthetic pigments. Oxygenic photosynthesis is therefore a primary target in NASA’s search for life on habitable planets in other solar systems. An unanswered question is what the upper limit is to the photon wavelength at which oxygenic photosynthesis can remain viable. On other planets that have a parent star very different spectrally from our Sun, can we expect oxygen from plants of different colors from those on Earth?

    The cyanobacterium, Acaryochloris marina serves as a model organism for oxygenic photosynthesis adapted to low light and red-shifted light environments similar to what may be found on habitable planets orbiting M stars. Until A. marina was discovered in 1996, all known oxygenic photosynthesis relied on the pigment chlorophyll a (Chl a). A. marina instead uses chlorophyll d, which can absorb the far-red and near-infrared light in A. marina’s habitat. We use photoacoustics in the lab to measure the energy storage efficiency of A. marina with lasers, and molecular electrostatics modeling to surmise how replacement of Chl a by Chl d in A. marina affects arrangements within the photosystem molecules. We are finding that A. marina can perform oxygenic photosynthesis quite efficiently in its unique light niche.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • Astronomical Observations of Planetary Atmospheres and Exoplanets

    This task encompasses remote-sensing observations of Solar System and extrasolar planets made by the VPL team. These observations, while providing scientific exploration in its own right, also allow us to test our planetary models and help advance techniques to retrieve information from the astronomical data that we obtain. This can include improving our understanding of the accuracy of inputs into our models, such as spectral databases. This year we made and/or analyzed observations of Mars, Venus and Earth taken by ground-based and spaceborne observatories, to better understand how well we can determine planetary properties like atmospheric and surface temperature and pressure, when a terrestrial planet is observed only as a distant point of light.

    ROADMAP OBJECTIVES: 1.2 2.2 7.2
  • Stromatolites in the Desert: Analogs to Other Worlds

    In this task biologists go to field sites in Mexico to better understand the environmental effects on growth rates for freshwater stromatolites. Stromatolites are microbial mat communities that have the ability to calcify under certain conditions. They are believed to be an ancient form of life, that may have dominated the planet’s biosphere more than 2 billion years ago. Our work focuses on understanding these communities as a means of characterizing their metabolisms and gas outputs, for use in planetary models of ancient environments.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 5.3 6.1 6.2
  • Delivery of Volatiles to Terrestrial Planets

    We are investigating the mechanisms by which terrestrial planets obtain water and organic compounds. By understanding how these crucial constituents for life came to Earth, we can determine whether these mechanisms also operate in exoplanetary systems. When an earth-like planet is finally discovered in an exoplanetary system, it will be difficult to directly measure the composition of that planet. However, VPL scientists will use the observable properties of the system to determine whether that planet has a history that allowed water and organics to have been transported to it. One of the important questions is the initial state of the organic compounds, which sets stringent limits on the ability of the earth-like planets to acquire carbon.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.1 4.3
  • Earth as an Extrasolar Planet

    Earth is the only known planet that can support life on its surface, and often serves as the typical example of what a habitable planet looks like. In anticipation of future discoveries of observable, potentially habitable worlds around other stars, this task seeks to understand how we would characterize and understand the distant Earth. To accomplish this, we have developed several tools and approaches for simulating and investigating the Pale Blue Dot. In particular, we have demonstrated how an airless moon can affect observations of a habitable planet, developed new metrics to measure atmospheric pressure, and modeled light reflected off liquid water surfaces.

    ROADMAP OBJECTIVES: 1.2 7.1 7.2
  • VPL Databases, Model Interfaces and the Community Tool

    The Virtual Planetary Laboratory (VPL) develops computer models of planetary environments, including planets orbiting other stars (exoplanets) and provides a collaborative framework for scientists from many disciplines to coordinate their research. As part of this framework, VPL develops easier to use interfaces to its models, and provides model output datasets, so that they can be used by more researchers. We also collect and serve to the community the scientific data required as input to the models. These input data include spectra of stars, data files that tell us how atmospheric gases interact with incoming stellar radiation, and plant photosynthetic pigments. We also develop tools that allow users to search and manipulate the scientific input data. This year we provided Earth model datasets, new tools for searching the molecular spectroscopic database, and a new database of biological pigments. All of these products and others are published on the VPL Team Website at: http://depts.washington.edu/naivpl/content/models-spectra.

    ROADMAP OBJECTIVES: 1.1 1.2 3.2 4.1 6.1 7.1 7.2
  • Understanding Past Earth Environments

    For much of the history Earth, life on the planet existed in an environment very different than that of modern-day Earth. Thus, the ancient Earth represents a planet with a biosphere that is both dramatically different than the one in which we live, but that is also accessible to detailed study. As such, it serves as a model for what types of biospheres we may find on other planets. A particular focus of our work was on the “Early Earth” (formation through to about 500 million years ago), a timeframe poorly represented in the geological and fossil records but comprises the majority of Earth’s history. We have studied the composition and pressure of the ancient atmosphere; modeled the effects of clouds on such a planet; studied the sulfur, oxygen and nitrogen cycles; and explored atmospheric formation of molecules that were likely important to the origins of life on Earth.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
  • Dynamical Effects on Planetary Habitability

    The Earth’s orbit is near-circular and has changed little since its formation. The Earth is also far enough away from the Sun, that the Sun’s gravity doesn’t seriously affect the Earth’s shape. However, exoplanets have been found to have orbits that are elliptical, rather than circular, and that evolve over time, changing shape and/or moving closer or further to the parent star. Many exoplanets have also been found sufficiently close to the parent star that it can deform the planet’s shape and transfer energy to the planet in a process called tidal heating. In this VPL task we investigate how interactions between a planet’s orbit, spin axis, and tidal heating can influence our understanding of what makes a planet habitable. Scientific highlights include modeling of habitable planets around brown dwarfs, the first comprehensive analysis of exomoon habitability, the role of distant stellar companions on planetary system architecture, and an improved understanding of the origins of terrestrial planet composition.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3
  • Detectability of Biosignatures

    In this project VPL team members explore the nature and detectability of biosignatures, global signs of life in the atmosphere or on the surface of a planet. This year we submitted for publication modeling work that explores the potential for non-biological generation of oxygen and ozone in early Earth-like atmospheres, which could result in a “false positives” for photosynthetic life. In parallel, we worked with three simulators for telescopes that will one day be able to observe and determine the properties of extrasolar terrestrial planets, and used these simulators to calculate the relative detectability of gases produced by life.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 7.2
  • Stellar Radiative Effects on Planetary Habitability

    Habitable environments are most likely to exist in close proximity to a star, and hence a detailed and comprehensive understanding of the effect of the star on planetary habitability is crucial in the pursuit of an inhabited world. We looked at how the Sun’s brightness would have changed with time providing wavelength-dependent scaling factors for solar flux anywhere in the solar system from 0.6 to 6.7Gyr. Extrasolar planetary systems can only be determined through studying the host star; therefore we have also worked on determining the ages of Kepler planet host stars. We have constructed far ultraviolet to mid-infrared stellar spectra for 44 stars for being used as input in climate and photochemical models that are applied for determining habitable zones and possible characteristics of habitable planets. We have looked into the effect of methane (CH4) and hydrogen (H2) on the outer edge of the habitable zone for F, G, and M stars. We have studied the effect of host star stellar energy distribution (SED) and ice-albedo feedback on the climate of extrasolar planets.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 4.1 4.3 7.2
  • The VPL Life Modules

    The VPL Life Modules involve development of simulation models of how biological processes – such as photosynthesis, breathing, and decay of organic materials – work on a planetary scale. When this is combined with the work of the atmospheric and planetary modeling teams, we are able simulate how these processes impact the atmosphere and climate of a planet. This information helps us understand how we might be able to detect whether or not a planet has life by looking at its atmosphere and surface. The Life Modules team has engaged in previous work coupling early Earth biogeochemistry and 1D models in the VPL’s suite of planetary models. Current work now focuses on the development of a land biosphere model coupled with a previously developed ocean biogeochemistry model and a 3D general circulation model (GCM). This terrestrial biosphere model is designed to simulate geographic distributions of life adapted to different climate zones, surface albedo, and carbon dioxide exchange and other biogenic gases with the atmosphere. These coupled models are first tested against Earth ground and satellite observations. A large data mining effort is now under way for the model of land-based ecosystem dynamics to uncover vegetation adaptations to climate that may be generalizable for both the Earth and alternative planetary environments.

    ROADMAP OBJECTIVES: 1.2 6.1 6.2 7.2