May 03, 2019 12:00p - 2:30p
May 03, 2019 12:00p - 2:30p
April 05, 2019 12:00p - 2:30p
March 01, 2019 12:00p - 2:30p
December 07, 2018 12:00p - 2:30p
Successfully launched in April 2018, the Transiting Exoplanet Survey Satellite (TESS) will discover thousands of exoplanets in orbit around the brightest stars in the sky. In its two-year prime survey mission, TESS is monitoring more than 200,000 bright stars in the solar neighborhood for temporary drops in brightness caused by planetary transits. This first-ever spaceborne all-sky transit survey will identify planets ranging in size from Earth-sized to gas giants, orbiting a wide variety of host stars, ranging from cool M dwarfs to hot O/B giants. TESS stars will typically be 30-100 times brighter than those surveyed by the Kepler satellite; thus, TESS planets will be far easier to characterize with follow-up observations. For the first time it will be possible to study the masses, sizes, densities, orbits, and atmospheres of a large cohort of small planets, including a sample of rocky worlds in the habitable zones of their host stars. An additional data product from the TESS mission will be full frame images (FFI) with a cadence of 30 minutes. These FFI will provide precise photometric information for every object within the 2300 square degree instantaneous field of view of the TESS cameras. In total, nearly 100 million objects brighter than magnitude I=16 will be precisely photometered during the two-year prime mission. TESS’s unique lunar-resonant orbit should provide opportunities for an extended mission lasting more than a decade. A deep survey by TESS of regions surrounding the North and South Ecliptic Poles will provide prime exoplanet targets for characterization with the James Webb Space Telescope (JWST), as well as other large ground-based and space-based telescopes coming online in the next two decades. A NASA Guest Investigator program is underway for TESS. The TESS legacy will be a catalog of the nearest and brightest main-sequence stars hosting transiting exoplanets, which should endure as the most favorable targets for detailed future investigations. Initial results from the first few months of the TESS mission will be presented.
November 02, 2018 12:00p - 2:30p
Photosynthesis is the most important bioenergetic innovation in the history of the biosphere and it engendered Earth’s most marked environmental change: the rise of oxygen. Photosynthesis dramatically increased global primary production and transformed Earth's chemical cycles. At the same time, this new photosynthetic source of oxygen brought about tremendous biological change. Oxygen rewrote life’s recipe book, facilitating evolution of the richness we associate with modern biology. In this talk I will present observations from a range of perspectives including genomes, chemistry, and the ancient sedimentary rock record to illustrate what we can learn about how this process emerged two-and-a-half billion years ago—drawing specifically on the special role of the element manganese in this history.
May 04, 2018 12:00p - 2:30p
From exoplanets, with their surprising lack of spectral features, to Titan and its characteristic haze layer, numerous planetary atmospheres may possess photochemically produced particles of "haze". With few exceptions, we lack strong observational constraints (in situ or remote sensing) on the size, shape, density, and composition of these particles. Photochemical models, which can generally explain the observed abundances of smaller, gas phase molecules, are not well suited for investigations of much larger, solid phase particles. Laboratory investigations of haze formation in planetary atmospheres therefore play a key role in improving our understanding of the formation and composition of haze particles. I will discuss a series of experiments aimed at improving our understanding of the physical and chemical properties of planetary atmospheric hazes on Titan, Pluto, super-Earths, and mini-Neptunes.
April 06, 2018 12:00p - 2:30p
To most thoroughly understand exoplanetary systems, in both individual and statistical senses, requires a thorough characterization of their host stars. Whether or not a host star has companions, and the properties of those companions, directly affects the measured radii of transiting exoplanets. How active or jittery a host star is dictates the precision and accuracy with which we can measure the masses of orbiting planets. And recent work is showing how host star composition serves as an important piece of the exoplanet composition puzzle. In this talk I will discuss how I am using high resolution imaging and spectroscopic studies of host stars to investigate the properties and diversity of exoplanets in the Galaxy.
March 02, 2018 12:00p - 2:30p
How to recognize signs of life in past sediments from Earth or other planets? Sedimentary record from the first 80% of Earth’s history preserves signatures of microbial life, but these biosignatures can often be difficult to recognize or interpret. Specifically, it is often unclear to what extent microbial metabolisms and microbial interactions with minerals and sediments promote fossilization in siliciclastic sediments. This talk will highlight some questions that arise from the record on the early Earth and address them by taphonomic experiments. The utility of these insights will be also discussed in the context of the search for life on early Mars.
February 02, 2018 12:00p - 2:30p
Are we alone in the Universe? The search for life beyond Earth is the most compelling scientific question of our time; a positive detection would be one of the most profound discoveries ever made by humanity. Chemical evidence of habitable conditions and organic compounds make Saturn's moon Enceladus a promising lead in the search for life beyond Earth. What makes Enceladus truly unique is the confirmed and sustained plume of water ice, gases, and salts ejected into space through a system of vents and fissures in the moon’s South Polar Terrain. The composition of the plume points to a level of organic chemical evolution never before observed outside the Earth; and the plume itself makes ocean materials accessible to an orbiting spacecraft at significantly lower risk than landing. In this lecture I will review the clues obtained by the Cassini mission, which lead to the astonishing conclusion that there is a habitable ocean beneath the moon’s icy crust. I will also discuss a mission strategy to search for evidence of life in the ocean through the analysis of materials sampled from the plume, as well as some of the key technological hurdles that such a mission would have to face.
December 01, 2017 12:00p - 2:30p
Where is the best place to find living life beyond Earth? It may be that the small, ice-covered moons of Jupiter and Saturn harbor some of the most habitable real estate in our Solar System. Life loves liquid water and these moons have lots of it! Dr. Hand will explain the science behind why we think we know these oceans exist and what we know about the conditions on these worlds. He will focus on Jupiter’s moon Europa, which is a top priority for future NASA missions. Dr. Hand will also show how the exploration of Earth’s ocean is helping to inform our understanding of the potential habitability of worlds like Europa. Dr. Hand was a scientist onboard James Cameron’s 2012 dive to the bottom of the Mariana Trench, and he was part of a 2003 IMAX expedition to hydrothermal vents in the Atlantic and Pacific oceans. He has made nine dives to the bottom of the ocean.
November 03, 2017 12:00p - 2:30p
Mars is the only other planet besides Earth with multiple lines of geomorphic and spectral evidence for the past existence of flowing water on the surface. In the current climate, water on Mars exists almost entirely in the form of ice and in minor form as a gas. The notion of contemporary liquid water on Mars has been controversial. Pure liquid water on the surface would be rapidly lost to the tenuous atmosphere of Mars via evaporation; however, brines can be stable on the Martian surface for an extended period due to their lower eutectic temperature and evaporation rate. One of the major Mars discoveries of recent years is the existence of recurring slope lineae (RSL), which suggests that liquid water may occur on or near the surface of Mars today. Recently, hydrated oxychlorine salts, including perchlorates, were spectrally detected at sites hosting RSL which implicates that water does play a role in the formation of RSL, although the magnitude of the role is uncertain. If RSL are indeed contemporary brines on Mars, they might provide transiently wet conditions near the surface on Mars, although the water activity in oxychlorine-salt solutions may be too low to support known terrestrial life. Widespread perchlorates may also challenge our ability to characterize some organic species via traditional pyrolysis experiments on Mars because of their reactivity with organics. Further astrobiological characterization and exploration of these unique regions on Mars are necessary to fully assess the current habitability of Mars.
October 06, 2017 12:00p - 2:30p
Informed by comparative planetology and a survey of the major episodes in Earth history, this lecture will offer taxonomy of planetary catastrophes meant to illuminate the unusual nature of the “Anthropocene”, the current era of human-driven planetary scale changes, and reframe our current environmental and technological predicaments as part of a larger narrative of planetary evolution. This saga has now reached the pivotal moment when humans have become a dominant force of planetary change, and geological and human history are becoming irreversibly conjoined. Is this a likely or even inevitable challenge facing other complex life in the universe? Possible implications for exoplanet characterization and SETI will be considered, as well as the choices our civilization faces in attempting to create a wisely managed Earth.
April 07, 2017 12:00p - 2:30p
The habitable zone is the circular region around a star in which liquid water could exist on the surface of a rocky planet. Currently established definitions of the habitable zone have adopted an Earth-centered approach, assuming that the most common greenhouse gases on our planet (CO2 and H2O vapor), and a habitable zone that is calibrated to that of our present day Sun, applies to all other stellar systems irrespective of age, stellar class, or other potentially key greenhouse gases. Here, I argue that such an approach is causing us to overlook many potentially habitable planets on our target list. Not only is the temporal evolution of the habitable zone critical for assessing planetary habitability, but other greenhouse gases, such as hydrogen, can significantly extend the width of the traditional CO2-H2O habitable zone. I also discuss the potential habitability of Proxima Centauri b and the TRAPPIST-1 planets within the context of my revised habitable zone definitions.
March 03, 2017 12:00p - 2:30p
The fundamental goals of Astrobiology are focused on understanding the origin, distribution, and future of life in the universe. Currently, the unique example of 'life' available to us is from Earth -- 'life as we know it'. It was recognized, before the launch of Sputnik, that overprinting with contaminants from Earth could prevent the detection of extraterrestrial life -- and also that the inadvertent release of extraterrestrial organisms into the Earth's environment could have adverse consequences. The precautions taken to prevent these possibilities are called Planetary Protection.
October 28, 2016 12:00p - 2:30p
The study of exoplanetary atmospheres is one of the frontiers of exoplanet science. It enables us to remotely sense the surface (or photospheric) environment of an exoplanet and ask questions related to chemistry and formation history. In the first part of the talk, I will give a brisk review of the tools of the trade: the assumptions and concepts that go into constructing a model atmosphere. I will focus on the caveats and challenges associated with opacities, billion-line radiative transfer and chemistry. In the second part of the talk, I will apply these concepts towards the study of the four directly imaged exoplanets in the HR 8799 system. I will review why the radii and surface gravities of these exoplanets are model-dependent and somewhat controversial. I will dissect our implementation of a nested sampling atmospheric retrieval tool and explain why our retrieved elemental abundances and carbon-to-oxygen ratios are, at zeroth order, inconsistent with exoplanet formation via gravitational instability. Finally, I will share some (speculative) thoughts for the future, including on the habitable zone, geochemical cycles, biosignature gases (and false positives) and astrochemistry.
October 07, 2016 12:00p - 2:30p
In this talk, I discuss what aspects of life are likely to be universal, focusing primarily on the universal genetic code, but also the phenomenon of homochirality. I begin by relating life processes to the laws of physics. Then I show that relics of early life, preceding even the last universal common ancestor of all life on Earth, are present in the structure of the modern day canonical genetic code --- the map between DNA sequence and amino acids that form proteins. The code is not random, as often assumed, but instead is now known to have certain error minimisation properties. How could such a code evolve, when it would seem that mutations to the code itself would cause the wrong proteins to be translated, thus killing the organism? Using digital life simulations, I show how a unique and optimal genetic code can emerge over evolutionary time, but only if horizontal gene transfer --- a network effect --- was a much stronger characteristic of early life than it is now. These results suggest a natural scenario in which evolution exhibits three distinct dynamical regimes, differentiated respectively by the way in which information flow, genetic novelty and complexity emerge. Possible observational signatures of these predictions are discussed.
April 01, 2016 12:00p - 2:30p
Europa is one of the most enticing targets in the search for life beyond Earth. With an icy outer shell hiding a global ocean, Europa exists in a dynamic environment where immense tides from Jupiter potentially power an active deeper interior and intense radiation and impacts bathe the top of the ice. These processes are sources of energy that could sustain a biosphere. In this presentation, we will explore environments on Europa and their analogs here on Earth. NASA will launch a mission to Europa in 2021, but while we wait to get there, we are looking to our own cosmic backyard, Antarctica, to help us to better understand how Europa works. I will describe our work on the McMurdo Ice Shelf using ice penetrating radar and under ice robotics to study ice-ocean interactions and exchange in this Europa-like environment, and to develop techniques for exploring Europa as an ice covered world not so unlike our own.
March 04, 2016 12:00p - 2:30p
Planetary water-rock interfaces generate energy in the form of redox, pH, and thermal gradients, and these disequilibria are particularly focused in hydrothermal vent systems where the reducing, heated hydrothermal fluid feeds back into the more oxidizing ocean. Alkaline hydrothermal vents have been proposed as a likely location for the origin of life on the early Earth due to various factors: including the hydrothermal pH / Eh gradients that resemble the ubiquitous electrical / proton gradients in biology, the catalytic hydrothermal precipitates that resemble inorganic catalysts in enzymes, and the presence of electron donors and acceptors in hydrothermal systems (e.g. H2 + CH4 and CO2) that are thought to have been utilized in the earliest metabolisms. Of particular importance for the emergence of metabolism are the mineral “chimneys” that precipitate at the vent fluid / seawater interface. Hydrothermal chimneys are flow-through chemical reactors that form porous and permeable inorganic membranes transecting geochemical gradients; in some ways similar to biological membranes that transect proton / ion gradients and harness these disequilibria to drive metabolism. These emergent chimney structures in the far-from-equilibrium system of the alkaline vent have many properties of interest to the origin of life that can be simulated in the laboratory: for example, they can generate electrical energy and drive redox reactions, and produce catalytic minerals (in particular the metal sulfides and iron oxyhydroxides - “green rust”) that can facilitate chemical reactions towards proto-metabolic cycles and biosynthesis. Many of the factors prompting interest in alkaline hydrothermal vents on Earth may also have been present on early Mars, or even presently within icy worlds such as Europa or Enceladus – thus, understanding the disequilibria and resulting prebiotic chemistry in these systems can be of great use in assessing the potential for other environments in the Solar System where life could have emerged.
February 05, 2016 12:00p - 2:30p
Tracing the chemical history of water during the formation of solar-type stars sheds light on both the origins of water in our own solar system and, more generally, the availability of water to all nascent planetary systems. One important clue comes from measured enrichments in deuterium relative to hydrogen (D/H) in various solar system water reservoirs relative to that of the bulk nebular gas. Specifically, large D/H enhancements are a product of water formation in very cold environments, facilitated by the presence of high energy particles and photons. These requirements point to two possible origins for solar system water: in situ chemistry in the outer regions of a protoplanetary disk or inheritance from the parent molecular cloud. Using a comprehensive treatment of high energy processes in protoplanetary disks, we find that ion-driven deuterium fractionation in disks is inefficient, especially in the midplane. This lack of cold water formation in the disk implies that the solar system likely inherited a large fraction of its water, and perhaps other primordial ices, from the parent molecular cloud. If the solar system's formation was typical, water should be a common ingredient during the planet formation process.
December 04, 2015 12:00p - 2:30p
The last 20 years has seen an explosion in the number of known planets beyond our Solar System. Recently, this has included the discovery of a handful of potentially habitable worlds. However, to test their habitability, and search these planets for signs of inhabitance, we require a mission that is designed - from the ground up - with exoplanet characterization in mind. That characterization will take place via anaylsis of spectra from exoplanets, which will yield inferences on the composition of and mass fluxes from the planet’s surface. Such a mission would face three sets of challenges in technology, community dynamics, and science. In this presentation, we will discuss how future space-based telescopes can overcome the technical challenges, how NASA’s Nexus for Exoplanet Systems Science is addressing the community dynamics challenges, and how we can leverage the resulting community to address the science questions.
October 02, 2015 12:00p - 2:30p
Despite its apparent diversity, all of life on planet Earth is descended from a common ancestor, has essentially identical core molecular biology, and almost certainly has sampled selectively from the possible chemical solutions to the problems that biology presents. Therefore, we have available for study only one example of life. This makes it difficult to make any deep inferences about what life might look like in general, a difficulty that translates into comparable difficulties in recognizing life should we encountered it in a NASA space mission, or attempt to search for it by spectroscopy or radiotelescopy from a distant extrasolar planet. Only if we could find a second example of biology, one having origins independent of the biology that we know, will it be possible to do experiments that might dislodge the intrinsic "earth-centricity" hampers most thinking about biology. Mars might offer such a second biosphere. However, despite increasing likelihood that life will be found on Mars, the frequency with which material travels between Earth and Mars by natural processes is sufficiently high as to make not unreasonable the expectation that the Martian biosphere and the Terran biosphere also share common features. Analysis of spectroscopic and/or radio telescopic signatures from extrasolar planets, absent a "little green men" signal, is likely to be nothing more than controversial. Thus, we may be forced to turn to the remaining option to generate a second example of life: Create our own example in the laboratory. This talk will focus on these themes.
May 01, 2015 12:00p - 2:30p
Super-Earths are a class of planet not known in our Solar System but common among exoplanets. Can life survive there, and how would we detect it? I will present work exploring life on such worlds, especially Super-Earths with atmospheres that retain substantial amounts of hydrogen, and hence which will have surface chemistries substantially different from our own planet's. Surprisingly, the chemical inputs and outputs of life can be worked out from simple assumptions (or knowledge, when we have the knowledge) about planetary chemistry and environment, and the necessary properties of life. Some basic properties of the chemistry of life can be worked out from first principles: it must 'feed on' an energy source, it must be made of complex molecules which must therefore be of intermediate redox state. In the context of an hydrogen-rich super-Earth, I will discuss how these allow us to understand what biosignature gases such life could make. Gases can come from energy-generating reactions, and these are mostly constrained by the environment in which life grows. Gases can come from photosynthesis, which is also constrained by the environmental chemicals from which life builds its biomass. In both cases, we can not only identify the gases but also estimate the production rate, and hence whether it is plausible that life can make a detectable level of the gas. The third class of gases - those made by secondary metabolism - are harder to predict. Some modeling can be done, and I will touch on the issue of what chemicals to model. Lastly, I will mention the range of habitats, and hence of planetary environments, that such life might inhabit. Life on Super-Earth may actually be much more common than life on true Earth-analogues, but alas might also be much harder to detect.
April 03, 2015 12:00p - 2:30p
A primitive ocean on Mars held more water than Earth’s Arctic Ocean, as revealed from isotopic measurements of water in the planet’s atmosphere. The young planet would have had enough water to cover the entire surface in a liquid layer about 450 feet (137 meters) deep. More likely, the water would have formed an ocean occupying almost half of Mars’ northern hemisphere, in some regions reaching depths greater than a mile (1.6 kilometers). The new estimate is based on detailed observations of two slightly different forms of water in Mars’ atmosphere. One is the familiar H2O, made with two hydrogens and one oxygen. The other is HDO, a naturally occurring variation in which one hydrogen is replaced by a heavier form, called deuterium. The new results show that atmospheric water in the near-polar region was enriched by a factor of seven relative to Earth’s ocean water, implying that water in Mars’ permanent ice caps is enriched by 8-fold. Mars must have lost a volume of water 6.5 times larger than the present polar caps to provide such large enrichment. The volume of Mars’ early ocean must have been at least 20 million km3. Based on the surface of Mars today, a likely location for this water would be in the Northern Plains, which has long been considered a good candidate because of the low-lying ground. An ancient ocean there would have covered 19% of the planet’s surface – by comparison, the Atlantic Ocean occupies 17% of Earth’s surface. It is possible that Mars once had even more water, some of which may have been deposited below the surface. Because the new maps reveal microclimates and changes in the atmospheric water content over time, they may prove to be useful in the search for underground water.
March 06, 2015 12:00p - 2:30p
The Cassini-Huygens mission to Saturn has discovered two places in the Saturn system where life may occur, and they each have very different things to teach us. The small moon Enceladus has jets of material that shoot water, salts, and organics into space, all measured by Cassini. With the indirect detection of a liquid water ocean beneath the surface, Enceladus may well host life and the jets provide a simple mechanism for detecting it. Titan, cold and devoid of liquid water on its surface, nonetheless has lakes and seas of liquid hydrocarbons. To seek life there is to test whether water is essential for life or simply one of several alternative liquid solvents for hosting life. I will describe the next steps in exploring each of these environments.
December 05, 2014 12:00p - 2:30p
The NASA Exoplanet Exploration Program (ExEP) is chartered by the NASA Astrophysics Division to implement the NASA space science goals of detecting and characterizing exoplanets and of searching for signs of life. The Program is responsible for space missions, concept studies, technology investments, and ground-based precursor and follow-up science that enables future missions and delivers mission Level-1 science. The ExEP includes the space science missions of Kepler, K2, and the proposed WFIRST/AFTA mission that includes both a microlensing survey for outer-exoplanet demographics and a coronagraph for direct imaging of gas- and ice-giant planets around nearby stars. Studies of probe-scale (medium class) missions for a coronagraph (internal occulter) and starshade (external occulter) explore the trades of cost and science and provide motivation for a technology investment program leading to the next decadal survey for NASA Astrophysics. Ground follow-up using the Keck Observatory contributes to the science yield of Kepler and K2, and mid-infrared observations of exo-zodiacal dust by the Large Binocular Telescope Interferometer help constrain the design and predicted science yield of the next generation of direct imaging missions. Technology development in high-contrast imaging for internal and external occulters enable the design of missions that fulfill the goal of detecting habitable worlds and looking for signs of life.
November 07, 2014 12:00p - 2:30p
The Milky Way is teeming with planets smaller than Neptune but bigger than Earth. Yet with no such planets in our own Solar System, our understanding of the composition, formation, and habitability of these alien worlds is still sketchy. After presenting the confusing portrait painted by the few available measurements of the masses, radii, and atmospheres of these small planets, I will highlight how telescopes like Hubble, Kepler, and Magellan might help clarify the picture through deep observations of a few already known exoplanets. Our best opportunity to fill in the details, however, will be to find more small planets transiting nearby, small stars. Such easy-to-observe systems would be the best targets for atmospheric characterization with JWST, potentially enabling the first detection of molecules in the atmosphere of a habitable planet. I will report progress from two ongoing efforts to find these planets before the launch of JWST: the ground-based MEarth Project, searching the smallest stars for cool transiting planets, and the all-sky Transiting Exoplanet Survey Satellite mission, launching in 2017 to find the nearest and brightest transiting exoplanet systems.
October 03, 2014 12:00p - 2:30p
The evolution of oxygenic photosynthesis and the resulting oxygenation of the atmosphere and oceans was arguably one of the most important events on the early Earth. In addition to setting the stage for the evolution of higher eukaryotic life forms, oxygen serves as a planetary-scale remotely detectable biosignature when searching for life on other planetary bodies. Cyanobacteria are the most evolutionarily ancient oxygenic phototrophs and use water as an electron donor for photosynthesis, producing oxygen as a waste product. However, it is thought that cyanobacteria didn’t immediately acquire the ability to oxidize water. There is a large difference in the redox potentials between water and hydrogen and sulfide commonly used by the more ancient anoxygenic phototrophs. Members of our group have speculated that an intermediate reductant such as Fe(II) could have bridged the gap and acted as a transitional electron donor before water. The widespread abundance of Fe(II) in Archean and Neoproterozoic ferruginous oceans would have made it particularly suitable as an electron donor for photosynthesis. We have been searching for modern descendants of such an ancestral "missing link" cyanobacterium in the phototrophic mats at Chocolate Pots, a hot spring in Yellowstone National Park with a constant outflow of anoxic Fe(II)-rich thermal water. We present the results of our physiological ecology and complementary biosignature study, which revealed that the cyanobacteria grow anoxygenically using Fe(II) as an electron donor for photosynthesis in situ.
April 04, 2014 12:00p - 2:30p
Blood Falls is an iron-rich, saline feature at the terminus of Taylor Glacier in the McMurdo Dry Valleys, Antarctica. Geophysical and geochemical data indicate that the source of this surface outflow originates below the glacier, however the extent of the subglacial brine remains unknown. The brine harbors a microbial community that persists, despite cold, dark isolation. In order to better understand this ecosystem, drilling into the subglacial source will be required. Antarctic subglacial environments, like astrobiological targets on extraterrestrial worlds, are pristine ecosystems that warrant protection. Modern ice drilling projects, such as those planned for Blood Falls, are developing clean access approaches to prevent the contamination of both the subglacial environment and the samples retrieved. In this talk I will highlight recent expeditions to Blood Falls, which collectively shape our current understanding of the Taylor Glacier ecosystem. The brine below Taylor Glacier is an example of the diversity of potential microbial habitats hidden beneath Antarctic ice and provides important insight into subice microbial community structure and function. Collaborative, interdisciplinary studies of Blood Falls, such as those presented here, will enable the development of relevant tools for geomicrobiological examination of other subglacial environments on Earth and help prepare us for the exploration of icy extraterrestrial targets.
March 07, 2014 12:00p - 2:30p
NASA's Cassini mission has revealed Saturn's larger moon Titan to be a world rich in the "stuff of life." Reactions occurring in its dense nitrogen-methane atmosphere produce a wide variety of organic molecules, which subsequently rain down onto its surface. If these molecules mix with water found in cryovolanic lavas or impact melts on Titan's surface, they may react to form biological molecules such as amino acids. In this presentation, I will report on experimental work seeking to determine the type and quantity of biomolecules formed under conditions analogous to those found in transient liquid water environments on Titan. These reactions are intriguingly similar to reactions that may have occurred on the early Earth, and provide clues to the origin of life on our own world and worlds throughout the universe.
February 07, 2014 12:00p - 2:30p
The Wide Field Camera 3 (WFC3) on HST provides the opportunity for spectroscopic characterization of molecular features in transiting exoplanet atmospheres, a capability that has not existed in space since the demise of NICMOS on HST and the IRS on Spitzer. WFC3's slitless grism design and the stable and reliable pointing and thermal environment of HST provide an excellent platform for high-precision spectroscopic monitoring of transiting exoplanet host stars. Additionally, the wavelength range of WFC3's long-wavelength grism covers several molecular absorption bands which are relevant to planetary atmospheres, most notably the 1.4 micron water band. I will present analysis of WFC3 transit and eclipse measurements for a number of highly irradiated, Jupiter-mass planets observed over several HST cycles, with a focus on confirming which planets exhibit water absorption 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, and I will describe our progress and plans towards resolving some of these questions.
December 06, 2013 12:00p - 2:30p
Humans evolved and developed, and are born and raised, in a 1g gravity field. In some sense we have no business being in space where there is “zero gravity” (more accurately, freefall or microgravity). This presentation will discuss some of the ways in which the body adjusts to the extreme environment of spaceflight, and some of the ways in which this adjustment is insufficient and what researchers are doing about it. These physiological issues will become more serious as preparations are made for long-duration flights to asteroids, the moon, or Mars. The speaker's own research, including studies on sensorimotor function in the lab and parabolic flight, will be emphasized. In addition, commercial suborbital space flights will be taking place in a few years, and the potential research that can be performed on these flights will also be discussed.
November 01, 2013 12:00p - 2:30p
In the cold and dense stages of star and planet formation, volatile molecules condense out on interstellar grains forming icy mantles. This condensation process results in a series of snowlines, or condensation fronts, whose exact locations are set by a combination of thermal and non-thermal adsorption and desorption processes. The icy grain mantles are also active chemical sites, resulting in a changing ice composition with time, typically to include an increasing fraction of complex organic molecules. The nature of these snowlines in protoplanetary disks are predicted to have large impacts on planet formation efficiencies, on the bulk compositions of the forming planets, and on the amount of prebiotic material available on planet surfaces. We have used a combination of IR and millimeter observations, theory, and laboratory experiments to characterize interstellar ices, snow line locations (i.e. where these ices are located), and the chemical and planet formation consequences of the exact locations of different snow lines. I will discuss how the outcome of these studies have impacted our understanding of ice formation during star and planet formation, and also future prospects as complete ALMA and the next generation of laboratory experiments come online.
October 04, 2013 12:00p - 2:30p
Recent advances in exoplanet observations and theoretical methods are leading to unprecedented constraints on the physicochemical properties of exoplanetary atmospheres, interiors, and their formation conditions. In this talk, I will present some of the latest results in this emerging frontier. I will present constraints on the atmospheric chemical compositions and temperature profiles for a variety of exoplanets based on infrared observations from a wide range of facilities including HST, Spitzer, and ground-based telescopes. I will discuss how these constraints are being used to understand various equilibrium and non-equilibrium processes in exoplanetary atmospheres, to develop new classification schemes for exoplanets, and to understand the conditions of their formation and subsequent evolution.
I will also present the latest constraints emerging on the atmospheres, interior structures, and formation environments of super-Earths, whose interior compositions span a wide gamut - from water worlds with thick volatile envelopes to super-Mercuries, lava planets, and carbon planets - thereby testing the limits of our understanding of planetary mineralogies and their equations of state under exotic astrophysical conditions. The exciting future prospects of characterizing exoplanetary atmospheres, interiors, and formation conditions, using current, upcoming, and future observational facilities will be discussed, along with several open questions of fundamental nature in the field.
May 03, 2013 12:00p - 2:30p
Identifying terrestrial planets in the habitable zones (HZs) of other stars is one of the primary goals of ongoing exoplanet surveys and proposed space-based flagship missions. In this talk, I will discuss about our recent results on new estimates of HZs around Main-sequence stars. According to our new model, the inner and outer HZ limits for our Solar System are at 0.99 AU and 1.67 AU, respectively, suggesting that the present Earth lies near the inner edge. Our model does not include the radiative effects of clouds; thus, the actual HZ boundaries may be broader than our estimates. Applying the new HZ limits to cool, low mass stars (M-dwarfs) in NASA's "Kepler" data, we find that potentially habitable planets around M-dwarfs are more common than previously reported. The mean distance to the nearest habitable planet may be as close as 7 light years from us.
April 05, 2013 12:00p - 2:30p
On Earth, microorganisms appear to inhabit all physical space that provides the minimum requirements for life. These include the availability of water, carbon, nutrients, and light or chemical energy. While these are generally abundant in surface or near-surface environments, their mode and distribution in the subsurface are poorly constrained. Nevertheless, it has now been shown unequivocally that archaea and bacteria inhabit deeply buried rocks and sediments where they contribute to biogeochemical cycles. All evidence suggests that these subsurface ecosystems are spatially enormous and diverse. On other planets, at least in our solar system, putative extant or extinct life would most likely reside underground or in massive ice shells. With a focus on near-by planets where landed missions are more than just a possibility, access to the subsurface will be highly desirable. Robust strategies for subsurface life detection on Mars, Europa, or other potential targets are poorly developed. The search for extant life or its biosignatures is scientifically and technologically extremely difficult; on Earth, it is a formidable but tractable challenge. Our cross-disciplinary team from the University of Southern California, the California Institute of Technology, the Jet Propulsion Laboratory, the Rensselaer Polytechnic Institute, and the Desert Research Institute (DRI) will develop field, laboratory, and modeling approaches aimed at detecting and characterizing microbial life in the subsurface—the intraterrestrials.
March 01, 2013 12:00p - 2:30p
In this talk, Glavin will describe the concept of a “habitable environment” and the requirements for life as we know it. Understanding the basic requirements for life and the prebiotic chemistry that led to the emergence of life on Earth will help guide our search for life on Mars. Glavin will also give an overview of NASA's Mars Science Laboratory mission with an update on the progress of the Curiosity rover and a summary of the analytical capabilities and measurement objectives of the SAM experiment. Curiosity is currently getting ready for the first SAM analysis of a drilled rock on Mars and will take a step closer to answering the question of whether Mars could have ever supported life.
February 01, 2013 12:00p - 2:30p
The final stages of the growth of a planet consist of violently energetic impacts, but new observations of the Moon and Mercury indicate that the energy of accretion does not remove all the water and carbon from the growing planet. Models demonstrate that rocky planets that accrete with as little as 0.01 wt% water produce a massive steam atmosphere that collapses into a water ocean upon cooling. The low water contents required indicate that rocky planets may be generally expected to produce water oceans through this process, and that an Earth-sized planet would cool to clement conditions in just a few to tens of millions of years. These results indicate that most rocky planets in our solar system and rocky exoplanets are likely to have been habitable early in their evolution, increasing the likelihood of life on the estimated 17 billion Earth-sized planets in the Milky Way.
November 02, 2012 12:00p - 2:30p
A promising path to the discovery and study of individual rocky planets in the Habitable Zone around a star is to search for planets around nearby M dwarfs, as their mass and smaller HZ planet orbits leads to a significantly larger Doppler radial velocity signal than that of the Earth on our Sun. Since the flux distribution mid-late M dwarfs peaks sharply in the NIR a stable high-resolution NIR spectrograph capable of delivering high RV precision in the bands is a promising route to detecting rocky planets. I will discuss significant advances in precision NIR spectroscopy that may help achieve this goal, on-sky tests with laser frequency combs, and the ongoing design and build of the fiber-fed Habitable Zone Planet Finder (HPF) high resolution spectrograph.
October 05, 2012 12:00p - 2:30p
Proteins play the primary functional role in nearly all of life's physiological processes. They are, themselves, the final products of the translation system, life's oldest and most highly conserved of these processes. The early expansion of protein functions and complex functional networks created the foundation from which cellular life emerged. Here, I describe ancient transitions in protein evolution that ultimately led to the sophisticated protein repertoire of the universal ancestor at the root of the tree of life.
May 04, 2012 12:00p - 2:30p
The first two billion years of life on Earth left scant, inconclusive material evidence of its existence, despite its undoubtedly complex and profound impact on our planetary system. As a consequence, many hypotheses about the origin of life and its early evolution are currently untestable. New lines of evidence are therefore necessary to construct a more precise, explanatory narrative relating these planetary events, and place them within an astrobiological context. The genomes of extant organisms can provide such a record, as they are descended from lineages that endured across nearly all geological time, and preserve within their sequences an accumulated signal of ancient evolutionary processes and events.
Using comparative phylogenomic analyses, ancient horizontal gene transfers between the ancestors of extant groups can be inferred, demonstrating the chimeric, coalescent nature of early evolution, with recombinations within transferred genes revealing the selective pressures that shaped these lineages. Such transfers also act as an internal calibration for the relative timing of evolutionary events early in the microbial history of life, analogous to the fossil stratigraphy that orders the history of complex life in later geological eras. The phylogenomic record even extends to the very ancient time before the Last Universal Common Ancestor (LUCA), as ancestral sequence reconstruction of protein families diverging before this time gives clues to the function of the most ancient proteins, and the evolution of the earliest biological processes.
April 06, 2012 12:00p - 2:30p
Over the past two decades, there has been an increasing awareness within the geological, microbiological, and oceanographic communities of the potentially vast microbial biosphere that is harbored beneath the surface of the Earth. With this awareness has come a mounting effort to study this potential biome -- to better quantify biomass abundance, activity, and biogeochemical consequences of this activity. In the Earth system, the largest deep subsurface biome is also the least accessible -- the deep igneous ocean subsurface biosphere. This subcrustal biosphere also has greatest potential for influencing global scale biogeochemical processes –the carbon and energy cycles for example, and other elemental cycles.
This talk will focus on recent studies designed to elucidate this subcrustal biosphere, and illustrate techniques and novel technologies employed to address them. Integrative approaches using molecular biological, in-situ experimental, mineralogical, and geochemical techniques will be illustrated.
March 02, 2012 12:00p - 2:30p
If planets could re-form or migrate inwards to just outside the Roche limit of white dwarfs stars, they would be warmed to Earth-like temperature for billions of years. These planets would be easy to detect in edge-on orbit via a large depth transit lasting a couple of minutes and repeating every 12 hours; thus, a ground-based transit survey of cool white dwarfs would be sensitive to Earth-sized planets in their habitable zones, should they exist in sufficient abundance. I will discuss the prospects for detection and characterization of Earth-like planets in the habitable zones of white dwarfs, as well as scenarios for planet formation and potential constraints on habitability.
February 03, 2012 12:00p - 2:30p
Several young gas giants in wide orbits (> 10 AU) have now been directly imaged. These exciting discoveries provide new insights into the formation and early atmospheric properties of giant planets. This talk will focus on recent attempts to measure the near-infrared spectra of two planets orbiting the star HR8799. These data have aided in the characterization of the planets’ cloud and chemical properties, but also highlight the many difficulties we face when modeling planet atmospheres.
The few planets imaged so far are just the beginning. New instruments, tailor made for high-contrast imaging, are coming online this year and will reveal dozens of young planets. These instruments will also obtain low resolution near-IR spectra of each new planet, providing a wealth of information across a wide range of planet masses and ages. Given the lessons we are learning from systems like HR8799, interpreting these data will be not be easy and significant observational and planet modeling obstacles must be overcome.
December 04, 2011 12:00p - 2:30p
Water is abundant on Earth, covering 75% of Earth's surface, and accounting for up to 0.1% of Earth's mass, yet Earth may in fact be a very dry world. Liquid water is not only key for life, but understanding the origin of Earth's water has important implications for habitability in both our solar system and in the numerous extrasolar planetary systems that have been discovered with planets within their star's habitable zones. This research question requires an interdisciplinary approach and is one of the themes for the UH NASA Astrobiology Institute (NAI). In the 1980's observations and models first suggested that comets might play a role in delivering water to Earth, and that the chemical fingerprint of this process was the D/H of ocean water. A more modern look at the problem now seeks to uncover all the issues related to the origin of Earth's water to identify the key unanswered questions and assess where these questions can best be answered by interdisciplinary approaches.
The UH NAI team is investigating the chemical composition of primitive bodies and evidence of aqueous processes in the early solar system, dynamical delivery of bodies to earth and the chemical signature of this delivery to earth. I will discuss the interdisciplinary perspective of the origin of Earth's water, in part as a consensus view from a recent workshop held in Iceland during Sep. 2011 to highlight where we are in our current understanding.
November 04, 2011 12:00p - 2:30p
Astronomy is entering an exciting new era where ground- and space-based observatories open windows on planetary systems increasingly similar to our own. In this talk I will give a brief overview of the search for exoplanets and discuss techniques that allow us to characterize the atmospheres of extrasolar planets. I will illustrate these from our work on detecting and characterizing exoplanets. I will also introduce a new observing technique that provides an exciting look into the atmospheres, clouds, and surface features of exoplanets. We are now applying this technique, rotational phase mapping, to ultracool brown dwarfs using both the Hubble and the Spitzer Space Telescopes. I will discuss the exciting first results from these studies and the future applications of the technique to super-earths and earth-like planets, as a step toward understanding planets in or near to habitable zones.
October 07, 2011 12:00p - 2:30p
In the next decade Mars will be visited by the most capable Rovers and instruments built to date. How will these missions find evidence of life on Mars and what does mean for us if there is no life detected. The robotic exploration of Mars and subsequent return of samples to earth will reveal a lot of information about our own origins whether or not life is discovered.
May 06, 2011 12:00p - 2:30p
Comets and carbonaceous chondrites are the remnants of molecular cloud material from which our Solar System formed. These bodies are considered to be primitive in the sense that they have been subjected to the least modification following accretion. Both comets and carbonaceous chondrites contain relatively large quantities of refractory organic macromolecular material. For many decades, a lack of consensus has existed as to the ultimate origin of these extraterrestrial organic solids, where confusion largely stems from the fact that throughout the Galaxy there exist many regions were extensive organo-synthesis occurs. Origins theories for primitive Solar System organic solids span from the lowest temperatures in the Interstellar Medium up to 1000 K in the inner Solar System. The best constraint on the origin of refractory organic solids is obtained by detailed studies of the organic solids directly. Using advanced spectroscopic techniques we have identified a plausible source for these organic solids and show that the organic solids in both comets and carbonaceous chondrites share a common origin. The broader implications of these results, both in terms of our understanding of the early history of the inner Solar System objects and the origin of life on Earth, lie in linking the unique properties of these organic solids to events that shaped the origin and evolution of Earth.
April 08, 2011 12:00p - 2:30p
As told by Maynard Smith and Szathmáry (The Major Transitions in Evolution, 1998) life's major transitions involve information and individuality. With equal justification, however, we can mark evolutionary milestones in terms of physiological innovation. A physiological complement to Maynard Smith and Szathmáry's list might include three major innovations associated with primary production (photosynthesis, oxygenic photosynthesis, and nitrogen fixation) and five that changed the face of heterotrophy (respiration, aerobic respiration, phagocytosis, bulk oxygen transport, and technology). Such a physiological perspective highlights interrelationships between evolving life and a physically dynamic planet. Geochemical data suggest that for much of the Proterozoic Eon, oxygen minimum zones of Earth's oceans tended toward euxinia. Under these conditions, nitrogen limitation would have favored primary producers capable of nitrogen fixation, as the geobiological record suggests. Despite the presence of oxygenic photoautotrophs, continuing anoxygenic photosynthesis likely played an important role in sustaining the redox structure of Proterozoic oceans. Late in the Neoproterozoic Eon, however, tectonic events appear to have nudged the biosphere toward a new state. Widespread rifting correlates with a switch from predominantly sulfidic to ferruginous waters in the OMZ; broadly coeval expansion of eukaryotes is consistent with the low sulfide tolerance exhibited by most eukaryotic clades. Four independent geochemical proxies suggest further redox transition 580-550 Ma, a time when rates of sediment accumulation increased markedly. Higher oxygen tensions and a receding challenge of anoxia likely facilitated animal diversification, but it was the evolution of anatomical mechanisms for bulk transfer that freed animals from the constraints of diffusion -- ushering in the age of bilaterians.
March 18, 2011 12:00p - 2:30p
The origin of life occurred in a complex geochemical environment, characterized by significant chemical and thermal gradients, fluid fluxes, cycles, and interfaces. These aspects of the prebiotic world are critical to understanding life's origins. Crystalline surfaces of common rock-forming minerals are likely to have played several important roles, including catalysis of key biomolecules; as interfaces for the selection, concentration and protection of those molecules; and as templates for the assembly of molecular structures. Thus mineral surfaces may have contributed centrally to the linked prebiotic problems of containment and organization by promoting the transition from a dilute "primordial soup" to highly order domains of molecules.
Robert M. Hazen, Senior Staff Scientist at the Carnegie Institution's Geophysical Laboratory and Clarence Robinson Professor of Earth Sciences at George Mason University, received the B.S. and S.M. in geology at MIT and the Ph.D. at Harvard University in earth science. He is author of 350 scientific articles and 20 books, including Genesis: The Scientific Quest for Life's Origin. A former President of the Mineralogical Society of America, Hazen's recent research focuses on the role of minerals in the origin of life, the co-evolution of the geo- and biospheres, and the development of complex systems. He is also Principal Investigator of the Deep Carbon Observatory, a 10-year project to study the chemical and biological roles of carbon in Earth's interior (http://dco.ciw.edu).
February 04, 2011 12:00p - 2:30p
In the coming decades, the search for life outside our Solar System will be undertaken using astronomical observations of extrasolar terrestrial planets. To better inform our search, the NASA Astrobiology Institute\'s Virtual Planetary Laboratory team uses a suite of computer models to explore the interaction between a terrestrial planet and its parent star. The resulting models allow us to simulate extrasolar terrestrial planetary environments and spectra, and to define and quantify likely signs of planetary habitability and life. This talk will discuss the VPL models and results to date, including the detectability of planetary habitability and potential signs of life from alternative biospheres.
December 10, 2010 12:00p - 2:30p
Over 400 planets have been found around nearby stars, but none of them is thought to be at all like Earth. The goal now is to identify rocky planets within the habitable zones of their stars and to search their atmospheres spectroscopically for signs of life. To do this, we need new space-based telescopes such as NASA's proposed Terrestrial Planet Finders or ESA's Darwin mission (all of which are indefinitely postponed at the moment). If spectra of extrasolar planet atmospheres can be obtained, the presence of O2, which is produced from photosynthesis, or O3, which is produced photochemically from O2, would under most circumstances provide strong evidence for life beyond Earth. But "false positives" for life may also exist, and these need to be clearly delineated in advance of such missions, if at all possible. I will also contrast my optimism about the search for complex life with the more pessimistic view expressed by Ward and Brownlee in their book, Rare Earth.
November 12, 2010 12:00p - 2:30p
A low-latitude distribution of continents may be a prerequisite for the global glaciations that appear to have affected Earth at least twice during the emergence of animals. However, a preponderance of low-latitude continents may also make Earth more susceptible to true polar wander, the process by which the mantle and crust spin relative to the fluid outer core to maintain rotational equilibrium. I will make a case for a pair of true polar wander events circa 800 million years ago that started a cascade of changes in the geochemical cycling between continents and oceans, and led to global glaciation. Did these changes in climate and ocean geochemistry finally allow the radiation of animals, or was it the first animals that modified geochemical cycling and climate?
October 08, 2010 12:00p - 2:30p
The oxygenation of the Earth's surface, which occurred ca. 2.3 billion years ago, is the earliest unambiguous imprint of biology on a planetary scale. Therefore, the search for molecular oxygen features prominently in the prospective search for life on extrasolar planets. However, the connections between the evolution of life and the evolution of the oxygen content of the Earth's atmosphere remain unclear. This talk will present emerging new perspectives on the Earth's transition from an anaerobic to an aerobic world.
September 03, 2010 12:00p - 2:30p
A fundamental challenge for astrobiology is to establish the relative contributions of chance versus predictability in the origin and evolution of life on our own planet. Thus, for example, all Earth-life creates metabolism from an interacting network of protein molecules that catalyze various biochemical reactions. Furthermore, early during evolution it had arrived at a standard set of 20 amino acid building-blocks with which to build each of these proteins. We now have good reason to think that many of these amino acids are formed in significant quantities throughout the galaxy - but so are many others - so would alien life be like us, and how could we possibly know?
June 18, 2010 12:00p - 2:30p
What is the best strategy for finding signs of life beyond the Solar System? Until recent years this was a purely philosophical question, but today we have the technical ability to search for signs of life on exoplanets around nearby stars, so the question is now a practical one. To start, we ask what kind of signs of life should we be looking for, and where should we be looking? Next we might ask about the methods we could use for such a search, and the kinds of evidence that we expect to obtain. Finally we can ask about the prospects for starting this search in the coming decade.
May 07, 2010 12:00p - 2:30p
The advent of cryogenic space-borne infrared observatories such as the Spitzer Space Telescope has lead to a revolution in the study of extrasolar planets and planetary systems. Already Spitzer has characterized the emergent infrared spectra of close-in giant exoplanets that orbit sun-like stars, using transit and eclipse techniques. Transits offer enormous advantages in characterizing the bulk properties (mass, radius) as well as the atmospheric composition of extrasolar planets. However, the nearest transiting and habitable extrasolar planet almost certainly does not orbit a Sun-like star. It orbits an M-dwarf star, and it could be a scant 10 parsecs distant from us, or even closer. After we find this unusual habitable world, we will characterize it using transit techniques. Already the ground-based MEarth survey has found a hot superEarth (T = 500 Kelvins) orbiting the M-dwarf star Gliese 1214, 10 parsecs from our own Sun. A space-based all-sky survey could extend the MEarth results to habitable-zone planets. When we have found such a world, the James Webb Space Telescope will be able to measure its atmospheric composition, and possibly even search for biosignatures.
April 09, 2010 12:00p - 2:30p
For the past decade missions to Mars have "followed the water". In this talk I will argue that future missions should begin directly searching for signs of life. The most important result from the recent Mars missions in this regard was the discovery of perchlorate by the Phoenix lander. Perchlorate could form the basis of a biological redox system on Mars. Furthermore, reanalysis of the Viking GCMS results suggests that perchlorate and organics may have been present at the Viking sites. Ice-cemented ground beneath dry permafrost in the high elevations of the Antarctic Dry Valleys provides a model for considering the search for signs of life at the Phoenix site.
March 05, 2010 12:00p - 2:30p
Formation scenarios of the solar nebula invoke two main reservoirs of water ice that may have taken part concurrently into the production of solids. In the first reservoir, which is located within the heliocentric distance of 30 AU, water ice infalling from the Interstellar Medium (ISM) initially vaporized into the hot inner part of the disk and condensed in its crystalline form during the cooling of the solar nebula (Kouchi et al. 1994; Chick & Cassen 1997). The second reservoir, located at larger heliocentric distances, is composed of water ice originating from ISM that did not suffer from vaporization when entering into the disk. In this reservoir, water ice remained mainly in its amorphous form. From these considerations, we discuss here the trapping conditions of volatiles in planetesimals produced within the outer solar nebula and their implications for the origin and composition of gas giant planets, their surrounding satellite systems and comets. In particular, we show that the formation of icy planetesimals agglomerated from clathrate hydrates in the solar nebula can explain in a consistent manner the volatiles enrichments measured at Jupiter and Saturn, as well as the composition of Titan's atmosphere.
February 05, 2010 12:00p - 2:30p
Iron and sulfur redox chemistry support chemoautotrophic subsurface microbial communities on Earth, and could potentially sustain a biosphere on Mars. In this talk, I will describe a highly productive ecosystem in an extreme natural environment that is supported by air, water, and iron sulfide minerals. Through integrating cultivation-independent molecular ('omic', imaging, and other) methods with geochemical approaches, it has been possible to begin to determine how these communities are structured and to unravel complex interdependencies, spatial organization, and evolutionary pathways.
January 08, 2010 12:00p - 2:30p
The terrestrial geologic record from actual rocks extends back to about 4.02 billion years ago (4.02 Ga). Before that time, what we know of the environment of the earliest Earth's surface from the time of formation to the start of the continuous rock record is constrained by inferences derived from chemical and isotopic studies of the oldest zircon grains (Zr-orthosilicate minerals) as old as 4.38 Ga found in younger rocks, physics of stars and how planets form, and molecular phylogeny. Silicate planets form hot, but cool on timescales shorter than the tectonic cycle. Bolide impacts subsequently become important modifiers of surface environments, but after the planetary "re-set button" was hit by the Moon-forming event, were more beneficial than deleterious to early forms of life. Surface temperatures were likely warm enough to stabilize liquid water even with a fainter young Sun since ca. 4.4 Ga. The oldest meta-igneous rocks are interesting in that aside from their antiquity, they are rather mundane mid-crustal lithotypes. Evidence from the Hadean zircons points to extensive recycling of crust at underthrust zones (plate tectonics?), generation of granitoid melts and of (widespread?) continental crust and liquid water. The oldest know meta-sediments (ca. 3.81-3.83 Ga) preserve chemical and isotopic signatures consistent with (but not proof of) elemental Sulfur metabolism, N-fixation, CO2-fixation, and photoferrotrophy. In sum, by the time the continuous rock record starts at ~3.7 Ga, all of the key features of the habitable Earth were already in place. To place firmer constraints on the establishment of the habitable Hadean, we need to find yet older rocks. I will provide an update on this quest.
December 04, 2009 12:00p - 2:30p
NASA's Stardust spacecraft returned samples from comet 81P/Wild 2 to Earth in January 2006. Examinations of the organic compounds in cometary samples can reveal information about the prebiotic organic inventory present on the early Earth and within the early Solar System, which may have contributed to the origin of life. Preliminary studies of Stardust material revealed the presence of a suite of organic compounds including several amines and amino acids, but the origin of these compounds (cometary vs. terrestrial contamination) could not be identified. We have recently measured the carbon isotopic ratios of these amino acids to determine their origin, leading to the first detection of a cometary amino acid.
November 06, 2009 12:00p - 2:30p
Phosphorus is a key element in biological systems, acting in cell replication as RNA and DNA, in cell structure as phospholipids, and in metabolism as ATP. Given its ubiquity in biochemistry, phosphorus was likely present in the origin or early evolution of life. I will discuss sources of phosphorus on the early earth, concentrating primarily on extraterrestrial sources of reduced oxidation state phosphorus compounds, and evidence that these sources were used by early biochemical systems. Additionally, I will show how these reduced oxidation state phosphorus compounds could act in prebiotic or early biochemical systems to generate both key biologic compounds and metabolic energy.