2014 Annual Science Report

VPL at University of Washington Reporting  |  SEP 2013 – DEC 2014

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

Field Sites
27 Institutions
13 Project Reports
58 Publications
5 Field Sites

Project Reports

  • Earth as an Extrasolar Planet

    Earth will always be our best example of a habitable world. By studying Earth as a single point of light, which harkens back to the famous Pale Blue Dot image of our planet, we can develop ideas and techniques for characterizing other potentially habitable planets around distant stars. These techniques focus on remotely measuring or detecting fundamental planetary and atmospheric properties—-composition, total atmospheric mass, temperature, and the presence of a surface ocean.

    ROADMAP OBJECTIVES: 1.2 7.2
  • Coupled Energy Balance Ecosystem-Atmosphere Modeling of Thermodynamically-Constrained Biogenic Gas Fluxes Project

    The thermodynamically-constrained fluxes of gases to and from a biosphere has profound, planet-wide consequences. These fluxes can directly control the redox state of the surface environment, the atmospheric composition, and the concentration of nutrients and metals in the oceans. Through these direct effects, they also create strong forcings on the climate, the redox state of the interior of the planet, and the detectability of the biosphere by remote observations. This is a theoretical modeling study to constrain biomass, productivity, and biogenic gas fluxes given a range of geologic parameters.

    ROADMAP OBJECTIVES: 1.1 1.2 5.2 5.3 6.1 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 determine the initial 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.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 5.2 6.1
  • Stellar Effects on Planetary Habitability and the Limits of the Habitable Zone

    In this task, VPL team members studied the interaction between stellar radiation (including light) and planetary atmospheres to better understand the limits of planetary habitability and the effects of stellar radiation on planetary evolution. Work this year included using climate models to recalculate the boundaries of the surface liquid water habitable zone planets of different masses, an exploration of the effect of a star’s spectrum on the rate at which a planet can exit a snowball state, and calculation of water loss from terrestrial planets with different fractions of atmospheric carbon dioxide. Atmospheric escape models were also used to illustrate how the pre-main sequence evolution of M-dwarf stars could strip the gaseous envelopes from mini-Neptune planets, transforming them into potentially-habitable, Earth-sized rocky bodies. In pioneering work, VPL researchers also showed that the pre-main sequence phase of an M-dwarf can lead to strong atmospheric escape of water on otherwise potentially habitable worlds, potentially rendering them uninhabitable. Observational work was also undertaken to characterize the frequency and characteristics of stellar flares on M dwarf stars from Kepler data, as input to future work on characterizing the effect of stellar flares on habitability.

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

    In this task, VPL team members use observations and theory to better understand how to detect and characterize extrasolar planets. Techniques to improve the detection of extrasolar planets, and in particular smaller, potentially Earth-like planets are developed, along with techniques to probe the physical and chemical properties of exoplanet atmospheres. These latter techniques require analysis of spectra to best understand how it might be possible to identify whether an extrasolar planet is able to support life, or already has life on it.

    ROADMAP OBJECTIVES: 1.2 2.2 7.2
  • Understanding Past Earth Environments

    This year, this interdisciplinary effort continued on two major fronts. First, we furthered the development and use of new techniques that help us characterize environmental conditions on ancient Earth. This included progress on our development of a technique for estimating the atmospheric pressure on Archean Earth, and the development and use other techniques for analyzing the chemistry of Archean lakes. We also used our existing models of ancient Earth to simulate other conditions consistent with the conclusions reached from these laboratory analyses.

    ROADMAP OBJECTIVES: 1.1 1.2 4.1 4.2 5.1 5.2 6.1
  • 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 (Chl 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 stars redder than our Sun.

    Previously under this project, with other co-investigators we spectrally quantified the thermodynamic efficiency of photon energy use in the chlorophyll d utilizing cyanobacterium, Acaryochloris marina str. MBIC11017, determining that it is more efficient than a Chl a cyanobacterium. The current focus of the project is aimed at understanding the adaptations of far-red/near-infrared (NIR) oxygenic photosynthetic organisms in general: what is their ecological niche where they are competitive against chlorophyll a organisms in nature, and what energetic shifts have been made in their photosynthetic reactions centers to enable their use of far-red/NIR photons. Field sampling and measurements are being conducted to isolate new strains of far-red utilizing oxygenic photosynthetic organisms, to quantify the spectral and temporal light regime in which they and previously discovered strains live in nature, and use these light measurements to drive kinetic models of photon energy use to ascertain light thresholds of survival.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • Understanding the Early Mars Environment

    In this task VPL team members use Mars mission data and atmospheric models to understand the early environment on Mars. Areas of research include: the atmospheric formation of salts that have been found on the Martian surface, Early Mars volcanism and atmospheric composition, and possible atmospheric means of warming early Mars. Several VPL team members are also active on the MSL mission and have contributed to scientific discussions of modern geochemistry and the ancient habitability of Mars.

    ROADMAP OBJECTIVES: 1.1 2.1
  • Solar System Analogs for Exoplanet Observations

    The worlds of our Solar System represent only a fraction of the planetary diversity that likely exists in our Universe. Nevertheless, by studying and characterizing Solar System worlds, we can develop general models that can be applied and tested on exoplanets. Furthermore, by observing planets in the Solar System and studying these data within the context of exoplanet observations, we can provide new context and understanding to exoplanet data. Work in this area this past year includes observations of Titan as seen by Cassini, as an analog for exoplanet observations of hazy worlds; mapping observations of Venus below its cloud deck as an analog for processes and observations of hazy worlds; and the study of multiple atmospheres in the Solar System to understand the basic processes that control their atmospheric temperature structure.

    ROADMAP OBJECTIVES: 1.2 7.2
  • 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
  • Charnay NAI NPP PostDoc Report

    My project focuses on the modeling of clouds and photochemical haze in the atmospheres of the early Earth and exoplanets. I use a 3D model, developed to simulate any kind of atmospheres, to study the formation, dynamics, climatic impact and observational features of clouds/haze. My first object of interest is GJ1214b, a mini-Neptune whose observations by HST revealed a cloudy/hazy atmosphere. The formation of such high and thick clouds is not understood. My second object of interest is the Archean Earth for periods with a methane-rich atmosphere leading to the formation of organic haze.

    ROADMAP OBJECTIVES: 1.2 4.1
  • Habitable Planet Formation and Orbital Dynamical Effects on Planetary Habitability

    This task explores how habitable planets form and how their orbits evolve with time. Terrestrial planet formation involves colliding rocks in a thin gaseous disk surrounding a newborn star and VPL’s modeling efforts simulate the orbital and collisional evolution of a few to millions of small bodies to determine the composition, mass and orbital parameters of planets that ultimately reach the habitable zone. After formation, gravitational interactions with the star and planet can induce short- and long-term changes in orbital properties that can change available energy to drive climate and illuminate the planetary surface. The VPL simulates these effects in known and hypothetical planetary systems in order to determine the range of variations that permit planetary habitability.

    ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3
  • Jon Toner NAI NPP Postdoc Report

    Aqueous salt solutions are critical for understanding the potential for liquid water to form on icy worlds and the presence of liquid water in the past. Salty solutions can form potentially habitable environments by depressing the freezing point of water down to temperatures typical of Mars’ surface or the interiors of Europa or Enceladus. We are investigating such low-temperature aqueous environments by experimentally measuring the low temperature properties of salt solutions and developing thermodynamic models to predict salt precipitation sequences during either freezing or evaporation. These models, and the experimental data we are generating, are being applied to understand the conditions under which water can form, the properties of that water, and what crystalline salts indicate about environmental conditions such as pH, temperature, pressure, and salinity.

    ROADMAP OBJECTIVES: 2.1 5.2 5.3