2013 Annual Science Report

VPL at University of Washington Reporting  |  SEP 2012 – AUG 2013

Executive Summary

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 three thousand planetary candidates – many of them smaller than twice the diameter of ... Continue reading.

Field Sites
28 Institutions
13 Project Reports
68 Publications
2 Field Sites

Project Reports

  • The Nature and Detectability of Astronomical 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 comprehensive 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. We also explored the detectability of molecular dimers, especially O2-O2 as potentially easier to detect biosignature gases for transit transmission observations.

    We also calculated maximum methane fluxes from the geological process of serpentinization, as a potential false positive for life, and looked at the nature and detectability of non-photosynthetic pigments as potential biosignatures for life on exoplanets. We also started work to develop new, more generalized biosignatures via measurement of thermodyamic and kinetic anomalies in planetary atmospheric compositions that are associated with life. We complemented this theoretical work with field work in caves dominated by sulfur-bacteria, to understand isotopic processing of sulfur by life, as a potential biosignature for life on Mars, or for planets with sulfur-domianted biospheres.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 7.2
  • Exoplanet Detection and Characterization: Techniques, Retrieval and Analysis

    In this task VPL team members use theoretical modeling and analysis to develop new techniques for detecting and characterizing extrasolar planets. These include developing new techniques for detecting exoplanets in transit data, especially those planets with unusual orbital properties. Team members also work to provide the underlying theory required to develop new remote-sensing techniques for probing planetary atmospheres. They also work on techniques and tests for the retrieval of information about planetary environments from exoplanet photometry and spectra.

  • Biogenic Gases From Anoxygenic Photosynthesis in Microbial Mats

    This lab and field project aims to measure biogenic gas fluxes in engineered and natural microbial mats composed of anoxygenic phototrophs and anaerobic chemotrophs, such as may have existed on the early Earth prior to the advent of oxygenic photosynthesis. The goal is to characterize the biogeochemical cycling of S, H, and C in an effort to constrain the sources and sinks of gaseous biosignatures that may be relevant to the detection of life in anoxic biospheres on habitable exoplanets.

    ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1 6.2 7.2
  • Climates and Evolution of Extrasolar Terrestrial Planets

    Planetary climate results from the interplay of a large number of different physical processes, including radiative heating and cooling, advection and dynamics, latent heating and cloud effects, atmosphere-interior interactions, and the presence of life. Atmospheres and climate then evolve through time due to interplay between these processes and longer-term effects, such as atmospheric escape, orbital evolution, and other dynamical interactions. Since planetary climate determines surface habitability, we can better understand how planets maintain habitability over long time periods by studying and modeling the large network of interactions that determine the atmospheric state of a planet and how it changes through time.

  • Habitable Planet Formation and Orbital Dynamical Effects on Planetary Habitability

    The VPL explores how variations in orbital properties affects the growth, evolution and habitability of planets. The formation process must deliver the appropriate ingredients for life to a planet in order for it to become habitable. After planets form, interactions between a habitable planet at its host star and/or other planets in the system can change planetary properties, possibly rendering the planet uninhabitable. The VPL models these processes through computer models in order to understand how the Earth became and remains habitable, as well as examining and predicting habitability on planets outside the Solar System.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3
  • The Long Wavelength Limit of Oxygenic Photosynthesis

    Oxygenic photosynthesis (OP) produces the strongest biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. Both are controlled by the properties of Chlorophyll a, its ability to perform the water-splitting to produce oxygen, and its spectral absorbance that is limited to red and shorter wavelength photons. We seek to answer what is the long wavelength limit at which OP might remain viable, and how. This would clarify whether and how to look for OP adapted to the light from red dwarfs or M stars, which emit little visible light but abundant far-red and near-infrared. Very recently discovered cyanobacteria have been found to harbor alternative chlorophylls adapted to spectral light environments very much like that of M stars. This projects uses field, lab, and modeling studies to study these far-red adapted cyanobacteria as analogues for extrasolar oxygenic photosynthesis pushing the long wavelength limit.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • Exoplanet Detection and Characterization: Observations

    In this task, VPL researchers use astronomical instrumentation to detect and measure the properties of exoplanets. They also study terrestrial planets in our Solar System that can serve as practice targets for exoplanet observational techniques. These observations help us to develop and understand the techniques and measurements required to learn about planetary environments. Although many of these observations are now made on planets that are too large, or too close to their stars to be habitable, once proven, these techniques can then be adapted to help characterize the smaller, cooler planets that may be habitable.

    ROADMAP OBJECTIVES: 1.2 2.2 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: 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.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • Earth as an Extrasolar Planet

    Earth is our only example of a habitable planet, or a planet capable of maintaining liquid water on its surface. As a result, Earth serves as the archetypal habitable world in conceptual studies of future exoplanet characterization missions, or in studies of techniques for the remote characterization of potentially habitable exoplanets. We seek to accurately simulate the time-, phase-, and wavelength-dependent appearance of the Pale Blue Dot, and to use these models to understand how to best recognize and characterize potentially Earth-like exoplanets.

  • Genetic Evolution and the Origin of Life

    In this task biologists and chemists use field and laboratory work to better understand the environmental effects on growth rates for freshwater stromatolites and the mechanisms that govern their adaptation to their environment. 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 understanding environmental impacts on evolution, and characterizing their metabolisms and gas outputs, for use in planetary models of ancient environments. This year we also started a new project looking at the chemical affinities of the building blocks of life, as a way to understand how life might have initially formed from these chemical precursors.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.2 5.3 6.1 6.2
  • Stellar Effects on Planetary Habitability and the Limits of the Habitable Zone

    In this task VPL Team members explore the interactions between a planet and its parent star and how these interactions affect whether or not the planet can support life. These interactions can be radiative, with light from the star affecting the planet’s climate, or UV from stellar flares affecting the radiation environment at the planet’s surface. Or they interactions can be gravitational, with the star periodically deforming planets on elliptical orbits and thereby transferring energy into the planet. Both radiative and gravitational effects can input too much heat into a planet’s environment and cause it to lose the ability to maintain liquid water at the surface. Research this year included looking at the limits of the habitable zone with new calculations, exploring how gravitational tidal energy could cause a planet to lose its ocean, and understanding the effects that tidal deformation and incoming stellar radiation would have on the habitability of exomoons.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1
  • 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, pressure and climate of the ancient atmosphere; the delivery of biologically available phosphorus; 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
  • 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.

    This year, team members used climate and interior models to demonstrated that broadening of carbon dioxide and water absorption by volcanically-released hydrogen in Mars early atmosphere may have been enough to raise the mean surface temperature of early Mars above the freezing point of water. We also looked for mechanisms that might have produced the abundant perchlorate molecule found on the Martian surface today.