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2012 Annual Science Report

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

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 two thousand planetary candidates – many of them smaller than twice the diameter of the Earth – which may reside in the habitable zones of their parent stars. Kepler’s large survey will improve our understanding of how common terrestrial planets are in the Galaxy, and the planned James Webb Space Telescope (JWST) will probe the atmospheric composition of super-Earths. In the longer term, we anticipate spaceborne telescopes, such as NASA’s Terrestrial Planet Finder concept, that can directly image and obtain spectroscopy of terrestrial extrasolar planets.

The VPL provides a scientific foundation for interpretation of data from extrasolar terrestrial planet detection and characterization missions such as Kepler, JWST and the TPF. To do this, the VPL uses information from Earth’s stages of evolution, and data provided by NASA’s Earth observing and planetary exploration programs, to validate and develop more comprehensive models of terrestrial planets. These models allow us to simulate and explore the likely diversity of extrasolar planet environments in advance of the more challenging observations. These models are primarily used to understand the radiative and gravitational effects of stars on the planets that orbit them. Combinations of model and fieldwork are also used to understand which biologically produced gases can produce a detectable “biosignature“in globally-averaged planetary observations. Finally, models and instrument simulators are used to understand how we can best extract information on a planet’s environment from data that has no direct spatial resolution and may be quite limited in other ways.

The team required to develop and run these models is necessarily highly interdisciplinary. Our research encompasses single discipline efforts that produce results pertinent to our overarching habitability and biosignatures focus, all the way through to highly interdisciplinary efforts where stellar astrophysicists, planetary climate modelers, orbital dynamicists, atmospheric chemists and biologists work together to determine the effects of stellar radiation and gravitation on the habitability of terrestrial planets.

Our Research This Year

Our research can be divided into five main tasks: Earth as an Extrasolar Planet, The Observer, Early Earth and Mars, The Habitable Planet, and The Living Planet.

Earth as an Extrasolar Planet.

The Earth as an Extrasolar Planet project was completed earlier this reporting period with the publication of the final papers from the collaboration between the VPL 3-D Earth model and the EPOXI mission science teams (Livengood et al., 2011). Synthetic datasets from these modeling tasks are available on the VPL website.

Ongoing analysis of the EPOXI Earth observations by Meadows and students includes exploration of the detectability of the N2-N2 dimer in near-infrared spectra of the Earth, as a new way of probing the bulk composition of terrestrial planet atmospheres (Schweiterman et al., 2012 in prep). We also developed a new retrieval technique to simultaneously extract temperature, albedo and surface composition information in the near-infrared from terrestrial planet spectra, and validated this using the VPL Earth model, and EPOXI spectra of Earth and Mars (Schweiterman et al., 2012 in prep).

The Observer

Additionally, as part of our Observer task, we have converted our radiative transfer model to generate transmission spectra and have validated this against ATMOS observations of the Earth. We have used the model to show that simultaneous measurements of the absorption features from the O2-O2 dimer molecule and molecular oxygen (O2) can be used as a new technique to probe planetary atmospheric pressure for oxygenated atmospheres (Misra et al., 2012, in prep). Robinson and Meadows also made conference presentations on detecting exomoons using spectroscopy of the host planet, and concepts for an L1 Earth observing mission for astrobiology. Evans continued work on comparisons between TPF-C, -I, and –O instrument and telescope simulators for the detectability of habitability markers and biosignatures on extrasolar planets. Bailey, Agol, Barnes, Raymond and collaborators continued their work searching for extrasolar terrestrial planets using radial velocity surveys and Kepler data (e.g. Fleming et al., 2012; Wisniewski et al., 2012; Anglada-Escude et al., 2012).

Early Earth and Mars:

David Catling and collaborators worked on the early history of the Martian environment, including understanding the environmental implications of light-toned layered deposits in the tropics (Sefton-Nash et al., 2012), silica-rich hot springs (Marion et al., 2011), and clay minerals (Ehlmann et al., 2012). They also opened up a debate on the contemporary presence or absence of Martian methane (Zahnle et al., 2011). In work in progress, they also investigated the photochemical formation of Martian salts (Smith et al., 2011)

Catling, Buick and colleagues have on problems related to the history of the Earth’s atmosphere and biogeochemical cycles, including understanding the history of atmospheric oxygen (Catling, 2011, 2012; Kasting et al., 2012). These studies presented data that suggest the oxidation of sulfur on the land back to 2.7 Ga, indicating the presence of an early land-based photosynthetic microbial biosphere (Stueeken et al., 2012). Work was also published in Nature, constraining ancient atmospheric pressure on the 2.7 Ga Earth from the size of fossil raindrop imprints (Som et al., 2012).

Mark Claire and Shawn Domagal-Goldman were coauthors on a high-resolution multi-proxy study of an Archean drill section. Combining geochemistry and modeling, they and their colleagues provided the best evidence to date for the presence of organic haze (and also methane itself) in the Early earth atmosphere (Zerkle et al., 2012). Additionally, Claire, Catling, Meadows and colleagues published a paper on the evolution of the solar flux, that is applicable anywhere in the solar system, for solar ages of 0 – 8 Gyr (Claire et al., 2012). By constraining an important unknown in paleo-chemistry and climate studies, this work should reduce uncertainty in our understanding of the evolution of planetary atmospheres. Claire also collected samples from the Atacama using a 2011 NAI/Lewis and Clark Fellowship, following up research started during his 2010 DDF award ‘Perchlorate, Water, and Life.’

Habitable Planets

VPL studies the habitability of exoplanets on several fronts, including formation, atmospheric properties, and orbital dynamics. This year, Sean Raymond and colleagues examined how the formation of the inner Solar System may have been shaped by the migration of Jupiter and Saturn (the “Grand Tack” model – Walsh et al. 2011; Pierens and Raymond, 2011). They also showed that debris disks and terrestrial planets should be correlated (Raymond et al., 2012) and that wide binary stars (separations >1000 AU) are actually more destructive to planetary systems than closer binaries (Kaib et al., 2012). Finally they explored the tidal evolution of planets around brown dwarfs (Bolmont et al., 2011), and the effect of the stellar spin history (Bolmont et al., 2012).

Jim Kasting, students and collaborators developed a new 1-D photochemical code that is applicable to dense, hot atmospheres that approach thermodynamic equilibrium at depth, e.g., hot Jupiters (Kopparapu & Kasting 2012). This group also worked on the incorporation of new k-coefficients from the 2010 HITRAN and HITEMP databases into their climate-chemical code to recalculate the boundaries of the liquid water habitable zone around different main sequence stars (Kopparapu et al., 2012, submitted). This team also included collision-induced absorption (CIA) of infrared radiation by H2 into their 1-D climate model and used it to show that a dense CO2-rich atmosphere containing 10 percent H2 could have brought early Mars up above the freezing point (Ramirez et al., 2012, submitted). Ramirez and others also explored how methane might act as a secondary greenhouse gas and switch from greenhouse to anti-greenhouse agent for planets around different star types (Ramirez et al., in prep). The team also modified a 1-D hydrodynamic escape code to model hydrogen rich primitive atmospheres of terrestrial planets, and Zugger led work on polarization and glint signatures of ocean exoplanets (Zugger et al. 2011).

Rory Barnes, students and collaborators continued to study the role of orbital dynamics and planetary habitability. This past year the team showed that tidal heating can trigger a runaway greenhouse on exoplanets and exomoons (Barnes et al. 2012, Barnes & Heller 2012, Heller & Barnes 2012), and performed studies of the tidal effects on brown dwarfs in the MARVELS survey (Fleming et al. 2012; Ma et al. 2012). Barnes and colleagues also assisted in ground-based observations of transits (Kundurthy et al 2011, 2012a,b; Becker et al. 2012), and organized a workshop on the connections between orbital dynamics and planetary climate.

Monika Kress with student Tin Tran presented work on the chemical formation of PAHs in protoplanetary disks, as a possibly mechanism to incorporate carbon into forming terrestrial planets (Kress et al., 2012; Tran et al., 2012)

David Catling worked on ocean chemistry on outer planet satellites (Marion et al., 2012) and the development of indices to determine the composite habitability of exoplanets (Schulze-Makuch et al., 2011). Robinson and Catling (2012) also developed a generalized, analytic radiative-convective model that could be used in the future to assess the thermal structure of planetary atmospheres and thus the surface temperature-pressure regime and habitability.

Ed Bolton has begun production runs aimed at quantifying CO2 draw-down from the atmosphere by weathering of soils derived from idealized granite and basalt rock types. This modeling is being done to find the influence of atmospheric composition, temperature, and infiltration rates on CO2 consumption.

The Living Planet

In this research area, VPL team members use modeling, and laboratory and field work, to understand the co-evolution of the biosphere with its environment, and the limits of life. This year, Nancy Kiang completed a version of a global vegetation structure dataset to utilize the latest MODIS products (land cover, leaf area index, albedo), as well as LiDAR from the Geoscience Laser Altimeter System aboard the Ice, Cloud, and Land Elevation Satellite (ICESat/GLAS) (vegetation height) to serve as both boundary conditions or as a performance evaluation dataset for the Ent Terrestrial Biosphere Model (Ent TBM). This data set is now being used in global simulations, off-line and in the Goddard Institute for Space Studies general circulation model (GISS GCM), to test the Ent TBM for global scale simulations of carbon fluxes and leaf growth, estimation of carbon stocks in biomass, and improved predictions of surface albedoes. These tests will set the stage for experiments on exoplanet biosphere modeling.

Kiang, with postdoc Mielke and colleagues continue their work on Acarychloris marina and the efficiency of photosynthesis at longer wavelengths (Mielke et al., 2012). Kiang also led creation of a new database for photosynthetic pigments which is available for community use on the VPL website ( Janet Seifert continues to study the biology of Cuatro Cienegas, and was prominently featured with four publications in Astrobiology, including a paper on possible survival strategies for microbial stowaways to Mars (Siefert et al., 2012).

As part of an NAI DDF effort, Deming, Bowman and collaborators are continuing to test and modify the design on a cryoreactor for frost flowers and geochemistry (CRYO-FROG), achieving stable temperatures in the desired experimental range, in advance of conducting an initial set of experiments later this year.

Education and Public Outreach

The UW VPL contingent hosted the Lakewood High Astrobiology class again this year, and the class pioneered under NAI funding has now been picked up by the school as a permanent course. Work continues on a new web-based tool for exploring the habitable zones around stars in the local solar neighborhood. Deming participated in an outreach event at Toppenish (WA) to families and middle and high school children from the Yakama Nation. Several of our scientists gave public lectures this year as part of the Transit of Venus and MSL at Mars events, and VPL research was featured in numerous popular science magazines, newspapers and television documentaries.

NAI-VPL Director’s Discretionary Fund researcher and UW graduate student Jeff Bowman collects samples of “frost flowers” from Arctic ice. These unusual structures concentrate salts and nutrients and may provide an extreme environment for life. NAI DDF funding is being used to develop equipment to grow and study these structures in the lab.

The Habitability of ExoMoons

This past year work by VPL Team members was highlighted on the cover of the Astrobiology Journal. On the left, work by VPL Team member Janet Siefert on freshwater stromatolites at Cuatro Cienegas and on the right, work by team member Rory Barnes, in collaboration with Rene Heller, examined the habitability of exomoons.

Same as above (i.e. please combine the two covers into one figure, with the above caption under it.