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"Do we have a chance that Opportunity has found fossils of complex organisms? There are the three rocks that may suggest this."
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The Virtual Planetary Laboratory – The Life Modules - Photosynthesis
Project Investigators: Robert Blankenship, Nancy Kiang
Other Project Members
David Mauzerall (Collaborator)Steven Mielke (Collaborator)Summary
Photosynthesis provides the foundation for nearly all life on our planet and produces unique life signs — atmospheric oxygen and pigment colors — that are detectable from space at the global scale. This project seeks to determine the adapative rules for why photosynthetic pigments absorb particular wavelengths of light, and to quantify what is the long wavelength limit for oxygenic and also anoxygenic photosynthesis. This work will allow us to predict the plausible spectral properties and detectable properties of photosynthesis on other planets, especially those orbiting M stars, where longer wavelengths of light dominate the planetary surface radiation.
Astrobiology Roadmap Objectives:
- Objective 5.1: Environment-dependent, molecular evolution in microorganisms
- Objective 6.1: Environmental changes and the cycling of elements by the biota, communities, and ecosystems
- Objective 6.2: Adaptation and evolution of life beyond Earth
- Objective 7.2: Biosignatures to be sought in nearby planetary systems
Project Progress
For the period July 1, 2007 – June 30, 2008, the Life Modules section of the VPL accomplished the following, all of which are directly responsive to the NAI’s Goal 5: Evolution, Environment, and Limits of Life, and Goal 7: Signatures of Life.
Ent Dynamic Global Terrestrial Ecosystem Model (DGTEM) development: In cross-cutting research with NASA Earth Science, Modeling, Analysis, and Prediction (MAP) program, the Ent DGTEM is being developed for coupling of a terrestrial biosphere with the atmosphere to simulate fluxes of energy, water vapor, and biogenic trace gases, cycles of growth and decay, and migration of vegetation types with changing climate. This past year, Ent photosynthesis and vegetation conductance have been coupled to two atmospheric general circulation models (GCMs), and the modules for soil biogeochemistry and seasonal growth were successfully tested on field data for several vegetation types. More advanced canopy radiative transfer and dynamics of mortality, disturbance, and migration are being introduced this coming year. (Note that this work now replaces earlier efforts with the Community Land Model 3.0 of the National Center for Atmospheric Research). The VPL Life Modules group is currently collaborating with the Columbia Astrobiology Center (CAC) at Columbia University to couple an extrasolar version of the Ent DGTCM to the Terrestrial Planet Global Climate Model to allow 3-D modeling of extrasolar planet environments.
Energy efficiency limits of oxygenic photosynthesis: Additionally, we have started a new collaboration to work on “Thermodynamic efficiency of electron-transfer reactions in the Chlorophyll d-containing cyanobacterium, Acharyochloris marina.” to probe the long wavelength limits of oxygenic photosynthesis likely to be relevant for planets orbiting M stars. This work will be performed primarily by new NAI postdoctoral scholar Steve Mielke, under the guidance of Nancy Kiang and Robert Blankenship, and outside collaboration with David Mauzerall at Rockefeller University.
Figure 1. Diagram of the process modules of the Ent Dynamic Global Terrestrial Ecosystem Model and its couplings to the land surface and the atmosphere.Figure 2. Annual courses of measured (red) and modeled (black) daily sums of net CO2 fluxes (photosynthesis minus plant and soil respiration) for predicted by the Ent Dynamic Global Terrestrial Ecosystem Model (Ent DGTEM) for 3 different ecosystem types: a) C3 annual grassland, Vaira Ranch, California. b) boreal forest, Hyytiala Forest, Finland c) Western broadleaf deciduous forest, Morgan Monroe State Forest, Indiana.Figure 3. Winter (left) and summer (right) gross primary productivity calculated by Ent for the GISS GCM’s 8 vegetation cover types in a mid-20th century climate. Overestimate of GPP at 168 Pg-C/yr (observed range 90-120 Pg-C/yr) is typical of DGVMs not yet constrained by nitrogen limitation.Figure 4. Cover illustration for April 2008 Scientific American article, “The Color of Plants on Other Worlds,” on the work of VPL team members published in Astrobiology in 2007.Mission Involvement
MODISThe Ent Dynamic Global Terrestrial Ecosystem Model (DGTEM) relies heavily on both field and satellite data to drive and test its various submodules. MODIS data will be used to test albedo, leaf area, seasonal timing, and vegetation cover predictions of Ent.Terrestrial Planet Finder (TPF) – CoronagraphVPL research on the long wavelength limits of oxygenic photosynthesis will help define observational goals for TPF for plausible biosignatures. The coupled Ent DGTEM-TPGCM will provide a means to interpret disk-averaged data as the result of heterogeneous surface and atmospheric processes.Cross-Team Collaborations
Identify collaborative research with members of other NAI Teams during this reporting period. Include such details as the specific Teams, individuals involved, and the outcome of the collaborations.
The Columbia Astrobiology Center (CAC) at Columbia University is not yet an NAI team, but has applied for the next CAN cycle. VPL Life Modules member Nancy Y. Kiang is collaborating with CAC members Anthony Del Genio (climate dynamicist), Linda Sohl (paleoclimatologist), and Michael New (programmer). This effort will couple an extrasolar version of the Ent Dynamic Global Terrestrial Ecosystem Model (DGTEM) with the CAC’s Terrestrial Planet Global Climate Model (TPGCM), a version of the NASA GISS GCM being modified to simulate extrasolar planet climates.
- Astronomical Observations of Terrestrial Planet Atmospheres
- Earth as an Extrasolar Planet
- Effects of stellar flares on atmospheres of habitable planets
- Hydrodynamic Escape from Planetary Atmospheres
- Modeling Early Earth Environments
- Planet Formation and Dynamical Modeling
- Planetary Habitability
- Planetary Surface and Interior Models and Super Earths
- Stromatolites in the Desert: Analogs to Other Worlds
- The Virtual Planetary Laboratory – The Life Modules - Photosynthesis
- VPL Climate and Radiative Transfer Models
- VPL Model Interfaces and the Community Tool