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Project Reports

• Disks and the Origins of Planetary Systems

  This task is concerned with the evolution of complex habitable environments. The planet formation process begins with fragmentation of large molecular clouds into flattened disks. This disk is in many ways an astrochemical “primeval soup” in which cosmically abundant elements are assembled into increasingly complex hydrocarbons and mixed in the dust and gas within the disk. Gravitational attraction among the myriad small bodies leads to planet formation. If the newly formed planet is a suitable distance from its star to support liquid water at the surface, it is in the so-called “habitable zone.” The formation process and identification of such life-supporting bodies is the goal of this project.

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 4.1 4.3

• 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

• 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

• Circumstellar Debris and Planetesimals in Exoplanetary Systems

  This year, GCA astronomer Marc Kuchner invited the public to help him discover new planetary systems through a new website, DiskDetective.org. At DiskDetective.org, volunteers view data from NASA’s Wide-field Infrared Survey Explorer (WISE) mission and three other surveys. WISE measured more than 745 million objects, representing the most comprehensive survey of the sky at mid-infrared wavelengths ever taken.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1

• Biosignatures in Extraterrestrial Settings

  The Biosignatures in Extraterrestrial Environments group works on finding and characterizing exoplanets, in particular through very high resolution spectroscopy; and developing new techniques for finding exoplanets and characterizing their properties. It also works on understanding the evolution and dynamics of planetary systems, including the solar system, and the role of astrophysical processes in establishing and sustaining life in extraterrestrial environments.

  ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 4.1 4.3 6.2 7.1 7.2

• 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

• 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

• Evolution of Protoplanetary Disks and Preparations for Future Observations of Habitable Worlds

  The evolution of protoplanetary disks tells the story of the birth of planets and the formation of habitable environments. Microscopic interstellar materials are built up into larger and larger bodies, eventually forming planetesimals that are the building blocks of terrestrial planets and their atmospheres. With the advent of ALMA, we are poised to break open the study of young exoplanetesimals, probing their organic content with detailed observations comparable to those obtained for Solar System bodies. Furthermore, studies of planetesimal debris around nearby mature stars are paving the way for future NASA missions to directly observe potentially habitable exoplanets.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1 4.3 7.2

• Exploring the Structure and Composition of Massive Exoplanets

  We have analyzed exoplanet transit and eclipse measurements with the Hubble Space Telescope (HST) and the Spitzer Space Telescope for a number of highly irradiated, Jupiter-mass planets, with a focus on confirming which planets exhibit water absorption or emission in transit and/or eclipse and measuring the characteristic brightness temperature at these wavelengths. Measurements of molecular absorption in the atmospheres of these planets offer the chance to explore several outstanding questions regarding the atmospheric structure and composition of hot Jupiters, including the possibility of bulk compositional variations between planets and the presence or absence of a stratospheric temperature inversion. We are also developing simulations of future observations with the James Webb Space Telescope, and we are in the process of designing a future balloon-borne telescope to conduct a large survey of hot exoplanet atmospheres.

  ROADMAP OBJECTIVES: 1.1 1.2 7.2

• 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

• Titan as a Prebiotic Chemical System – Benner

  In 2007, NASA sponsored a committed of the National Academies of Science to explore whether life might exist in environments outside of the traditional habitable zone, defined as positions in a solar system where liquid surface water might be found. Alternative solvents which have analogous “habitable zones” farther away from their star include hydrocarbons, ammonia, and dinitrogen. The core question asked whether life having genetic biopolymers might exist in these solvents, which are in many cases (including methane) characterized by the need for “cold” (temperatures < 100K in the case of methane).

  These “weird” solvents would require “weird” genetic molecules, “weird” metabolic processes, and “weird” bio-structures. In pursuit of this “big picture” question, we turned to Titan, which has exotic solvents both on its surface (methane-hydrocarbon) and sub-surface (perhaps super-cooled ammonia-rich water). This work sought genetic molecules that might support Darwinian evolution in both environments, including non-ionic polyether molecules in the first and biopolymers linked by exotic oxyanions (such as phosphite, arsenate, arsenite, germanate) in the second.

  In the current year, we completed our studies that identified biopolymers that might work in hydrocarbon solvents. These studies have essentially ruled out biological processes in true cryosolvents. However, a series of hydrocarbons containing different numbers of carbon atoms (one, two, three, and four, for example, in methane, ethane, propane, and butane) cease to be cryosolvents as their chain lengths increase. These might be found on “warm Titans”. Further, they might exist deep in Titan’s hydrocarbon oceans, where heating from below would lead to warm hydrocarbon oceans.

  These studies showed that polyethers are insufficiently soluble in hydrocarbons at very low temperatures, such as the 90-100 K found on Titan’s surface where methane is a liquid at ambient pressures. However, we did show that “warm Titans” could exploit propane (and, of course, higher hydrocarbons) as a biosolvent for certain of these “weird” alternative genetic biopolymers; propane has a huge liquid range (far larger than water). Further, we integrated this work with mineralogy-based work that allows reduced molecules to appear as precursors for less “weird” genetic biomolecules, especially through interaction with various mineral species, including borates, molybdates, and sulfates.

  ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 3.4 4.1 5.3 6.2 7.1 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

• 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

• 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

• NNX09AH63A Origin and Evolution of Organics in Planetary Systems

  The Blake group has been carrying out joint observational and laboratory programs with NAI node scientists on the water and simple organic chemistry in the protoplanetary disk analogs of the solar nebula and in comets. Observationally, we continue to build on our extensive (>100 disks) Spitzer IRS survey of the infrared molecular emission from the terrestrial planet forming region of disks with follow-up work using the high spectral resolution ground-based observations of such emission (via the Keck and the Very Large Telescopes, the Herschel Space Observatory, SOFIA, and ALMA) along with that from comets. This year, we emphasized disk studies with the rapidly maturing capabilities of the ALMA observatory, that promises to revolutionize our understanding of the formation and migration of protoplanets, and with infrared studies of the molecular volatiles detectable in both comets and exoplanetary atmospheres. In the lab, we have continued to exploit our novel approach to broad-band chirped pulse microwave spectroscopy that promises to drop the size, mass and cost of such instruments by one to two orders of magnitude, and have developed a decade-spanning THz frequency comb with unprecedented precision. We are using these new instruments to measure the rotational spectra of prebiotic compounds, along with a detailed characterization of their large amplitude vibrations. Looking forward, these techniques have the potential to make site-specific stable isotope measurements, a capability we will continue to explore with GSFC Node scientists.

  ROADMAP OBJECTIVES: 1.1 1.2 3.1

• 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