2011 Annual Science Report

VPL at University of Washington Reporting  |  SEP 2010 – AUG 2011

Executive Summary

The Virtual Planetary Laboratory: Overview

The Virtual Planetary Laboratory is an interdisciplinary research effort focused 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, and the steps towards that endeavor are 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 a ... Continue reading.

Field Sites
33 Institutions
17 Project Reports
108 Publications
2 Field Sites

Project Reports

  • Evolution of Metabolism

    Our astrobiology research focus for VPL is to understand the evolution of different metabolic groups of microorganisms during the course of Earth’s history, and how the emergence of different metabolisms, such as methanogenesis, anoxic and oxygenic photosynthesis, and other anaerobic metabolisms that involve sulfur, metal, and nitrogen could effect the chemical composition of the atmosphere.

    ROADMAP OBJECTIVES: 5.1 5.3 6.2
  • The VPL Life Modules

    The Life Modules team at VPL works on developing 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, then, helps us understand how 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 biosphere models that simulate geographic distributions of life adapted to different climate zones and capable of coupling to 3D general circulation models (GCMs). Current project areas are: 1) development of a model of land-based ecosystem dynamics suitable for coupling with GCMs and generalizable for alternative planetary parameters, and 2) coupling of an ocean biogeochemistry model to GCMs.

    ROADMAP OBJECTIVES: 1.2 6.1 6.2 7.2
  • Postdoctoral Fellow Report: Steven Mielke

    This project seeks to resolve the long-wavelength limit of oxygenic photosynthesis in order to constrain the range of extrasolar environments in which spectral signatures of biogenic oxygen might be found, and thereby guide future planet detecting and characterizing observatories.

    ROADMAP OBJECTIVES: 5.1 6.1 6.2 7.2
  • Understanding the Early Mars Environment

    By analyzing data from rovers and orbiters, we construct theoretical models to constrain the habitability of current and past Martian environments. VPL has re-analyzed data and called into question the existence of methane and ancient oceans on Mars. In additional, we have contributed to past and future NASA missions such as Phoenix lander and the Curiosity rover,

  • 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 the star 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 the finding that tidal effects could be strong enough to cause a planet to overheat and ultimately lose its ocean, that large changes in the direction of the spin-axis of a planet could potentially increase the range of distances from the star in which the planet could remain habitable, and that the Sun may have moved significant distances outward through the Galaxy during its lifetime, changing the rate of at which large bodies have hit the Earth.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3
  • Delivery of Volatiles to Terrestrial Planets

    This project uses computer models and laboratory work to better understand how volatile materials that are important for life, like water, methane, and other organic molecules, are delivered to terrestrial planets. Habitable planets are too small to gravitationally trap these volatiles directly from the gas disk from which they formed, and instead they must be delivered as solids or ices at the time of the planet’s formation, or ongoing as the planet evolves. These trapped volatiles are eventually released to form our oceans and atmosphere. In this task we use computer models of planet formation and migration to understand how the asteroid belt, which is believed to be the source of the Earth’s oceans, was formed. We also use models to understand what happens to meteoritic material as it enters a planet’s atmosphere, especially where it gets deposited in the atmosphere, what happens to it chemically, and how it interacts with the light from the parent star. .

    ROADMAP OBJECTIVES: 1.1 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 serves as our only example of what a habitable planet looks like. This task uses distant observations of the Earth taken from spacecraft combined with a sophisticated computer model of the Earth to understand the appearance and characteristics of a habitable planet. With our model, we can generate accurate simulations of the Earth’s brightness, color and spectrum, when viewed at different time-intervals, and from different vantage points. This year we used these simulations to understand how we might detect the presence of an ocean on an exoplanet using polarization, and the presence of a moon around a distant exoplanet using heat energy, rather than visible light.

  • 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
  • Super-Earth Atmospheres

    In this task we use computer models to study aspects of the atmospheres of extrasolar super-Earths, planets that orbit other stars that are 2-10 times more massive than the Earth. Significant progress was made this year on two models, one that calculates how the atmosphere of the super-Earth is affected by radiative and particles coming from its parent star and one that calculates the surface temperature and change in atmospheric temperature with altitude for superEarth atmospheres.

    ROADMAP OBJECTIVES: 1.1 2.1 3.1
  • 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, 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.

  • Understanding Past Earth Environments

    For much of the history Earth, life on the planet existed in an environment dramatically 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 and is accessible to detailed study. As such, is 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 of the ancient atmosphere, modeled the effects of clouds on such a planet, studied the sulfur, oxygen and nitrogen cycles, and the 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
  • 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 surface temperature and atmospheric composition, when a terrestrial planet is observed only as a distant point of light.

    ROADMAP OBJECTIVES: 1.2 2.2 7.2
  • 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 completed and published our work on the build up and detectability of sulfur-based biosignatures in early Earth-like atmospheres, especially for planets orbiting stars cooler than our Sun. We also continued to explore the potential 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
  • 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
  • Postdoctoral Fellow Report: Mark Claire

    I have studied how biology might have impacted Earth’s early atmosphere, and how the Sun’s light has changed with time. More specifically, I’ve modeled how enhanced release of biogenic sulfur gases in earlier periods of Earth history may have left clues in the geologic record, and compared these predictions to the data. Furthermore, I have made a model of what how the light from the Sun would appear at any planet or any time in the solar system.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 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. We used models to study the effect of one very big flare on a planet with a carbon dioxide dominated atmosphere, like the early Earth’s, and found that these types of planets are well protected from the UV flux from the flaring star. We have also looked at the first quarter of Kepler data to study flare activity on “ordinary” cool stars, that have not been preselected for their tendency to have large flares. We find that these cool stars fall into two categories: stars that have long duration flares of several hours, but flare less frequently overall, and stars that have short duration flares, but more of them. In future work we will explore the comparative effect on a habitable planet of these two patterns of flaring activity.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 4.1 4.3 7.2
  • The Long Wavelength Limit for Oxygenic Photosynthesis

    Photosynthesis is process where plants and bacteria use solar energy to produce sugar and oxygen. It is also the only known process that produces signs of life (biosignatures) on a planetary scale. And, because starlight (or solar energy) is one of the most common sources of energy, it is expected that photosynthesis will be successful on habitable extrasolar planets. Our team is studying how photosynthetic pigments – the molecules that make photosynthesis possible – might function in unique or extreme environments on other planets. In our experiments, we use a bacteria called Acaryochloris marina to study how different photosynthetic pigments work. This bacterium is useful for our research because it uses a pigment known as chlorophyll d instead of chlorophyll a, which is more common on our planet. Chrolophyll a works well in Earth’s environment but, by studying chlorophyll d, we can begin to understand how photosynthesis might work on planets with different environments than Earth. So far, our research is revealing that photosynthesis can occur quite efficiently in environments that are very different from our planet.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2