Approximately half a dozen short presentations by UW Astrobiology faculty and students.
Formation and Detection of Habitable Exomoons
While about 4,000 planets and planet candidates have been found outside the solar system, no moon around an exoplanet (or "exomoon") has been found so far. New simulations indicate that moons similar in mass to planet Mars exist around the biggest planets outside the solar system, and recent advances in exomoon searching methods suggest that these large moons are observable with current and near-future technology. The detection of these moons would not only provide extremely valuable insights into planet formation and evolution, but could also reveal a recently predicted class of Mars-mass moons in the stellar habitable zones. These moons would be several times as massive as Ganymede, the most massive moon in the solar system, and they could be abundant extrasolar habitats with odd day-night cycles.
Is there Methane on Mars? III. Revenge of the Cows
The quest to measure methane has become a driver of 21st century Mars science. Dr. Zahnle will review why the published reports of methane on Mars should be regarded with skepticism, before addressing why the question may never go away.
The rise (and fall) of oxygen in Earth’s oceans and atmosphere and the co-evolution of early life
The oldest signs of animal life appear in the geologic record 600 to 700 million years ago. For the four billion years prior, our planet experienced dramatic changes that paved the way for this milestone. Beyond the establishment of the Earth’s earliest oceans perhaps as early as 4.4 billion years ago (Ga), the single most important environmental transformation in history may have been the first permanent rise of atmospheric oxygen around 2.3 to 2.4 Ga, at the so-called Great Oxidation Event (GOE). Before then, Earth’s atmosphere and oceans were virtually devoid of this gas, which forms the basis for all macroscopic life. Yet key questions remain about the timing and triggers of the first biological O2 production, now tentatively placed at 3 Ga, and the first appearance of animals almost two-and-half-billion years later. This talk will lay out the history of early oxygenation with an emphasis on the long delay between initial oxygenation and the expansion of complex life.
Recent work suggests that the initial rise of oxygen may have been protracted, occurring in fits and starts rather than a single step—and that once permanently present in the atmosphere, oxygen likely rose to very high levels and then plummeted. At least a billion years of dominantly oxygen-free conditions in the deep ocean followed beneath an atmosphere and shallow ocean that may still have been oxygen lean. Oxygen and associated nutrient deficiencies may, in turn, have set a challenging course for many of the ocean’s simple microscopic inhabitants, including persistently low populations and diversities of the earliest eukaryotic organisms. The newest data suggest that these billion-plus years of ‘intermediate’ oxygen and life were followed by increases in ocean/atmosphere oxygen contents and eukaryotic diversity that appear to anticipate the famous snowball Earth glaciation that began roughly 700 million years ago. The discussion will emphasize new proxy perspectives on these evolving redox conditions and their cause-and-effect relationships with early life.
Seeing Through the Clouds: The Thermal Emission and Reflected Light of Super-Earths with Flat Transmission Spectra
Vast resources have been dedicated to characterizing the handful of planets with radii between Earth’s and Neptune’s that are accessible to current telescopes. Observations of their transmission spectra have been inconclusive and do not constrain the atmospheric composition. Of the ~four small planets studied to date, all have radii in the near-IR consistent with being constant in wavelength, likely showing that these small planets are consistently enshrouded in thick hazes and clouds. I will explore the types of clouds and hazes that can completely obscure transmission spectra. I will then show the effect that these thick clouds have on the thermal emission and reflected light spectra of small exoplanets. I present a path forward for understanding this class of small planets: by understanding the thermal emission and reflectivity of small planets, we can potentially break the degeneracies and better constrain the atmospheric compositions.
Self-Organizing Chemical Systems: From Materials Science to Astrobiology
Self-organizing processes in chemical reaction/precipitation systems can lead to a variety of complex structures, including chemical gardens and inorganic membranes. They key aspects of these systems are the steep concentration gradients and far-from-equilibrium conditions, which in turn are determined by environmental and chemical factors. Chemical garden systems form complex self-organized structures and are now known to have many interesting and useful aspects, such as the ability to generate electrochemical energy and act as catalysts, and there is much interest in learning to control the precipitation process in such systems in order to produce useful materials. Chemical garden precipitates exist in nature as well, including hydrothermal chimneys, which form at the interface of contrasting seawater and vent fluids. Seafloor hydrothermal systems generate disequilibria through water-rock reactions in the form of redox, pH, chemical and thermal gradients; and the inorganic precipitates formed in these gradients could have played a role in prebiotic chemistry and the origin of life on the early Earth, and also could affect habitability and energy availability on other worlds with water-rock interfaces.
Wolf Clifton (Graduate Student, University of Washington)
Research Rotation Presentation: Growth of Cold-Adapted Bacteria Under Different Pressures and Temperatures
The subsurface ocean of Jupiter’s moon Europa is considered to be among the best prospective habitats for extraterrestrial life in our solar system. However, it is not known whether Earth organisms can grow at Europan seafloor pressures, which by many estimates exceed the maximum hydrostatic pressure observed in Earth’s oceans. Previous studies have shown a synergistic relationship between high temperature and high pressure tolerance for several organisms, suggesting that the warming effect of hydrothermal systems on the Europan seafloor could enable microbial growth under the high pressures experienced there. This rotation project sought to test the hypothesis that increased temperature boosts growth at high pressures for cold-adapted marine bacteria, using the organisms Colwellia psychrerythraea 34H and Psychrobacter strain P7E. These organisms were incubated at several combinations of temperature (8 and 18o C) and pressure (200, 400, and 600 atm), with cell counts taken periodically to measure growth over time. A synergistic relationship between temperature and pressure tolerance was observed for P7E, which grew better at 400 atm if the temperature was elevated to 18oC. No synergistic relationship was observed for 34H; nonetheless, the results are significant for demonstrating that 34H can grow at higher pressures than previously observed. Although the project’s findings do not directly address the question of whether Earth-like life can grow under Europan seafloor pressures, which greatly exceed those tested in this experiment, the results offer several insights relevant to astrobiology that may inform the design of future studies testing conditions for habitability in the Europan ocean and other high-pressure extraterrestrial environments.
Steven Wood (Research Assistant Professor, University of Washington)
Evidence, Explanation, and Implications for Recent, Cyclic, 20x Variation in the Mass of the Martian Atmosphere
The obliquity, or tilt, of Mars' spin axis is currently 25.19°, similar to that of the Earth, and seasonal variation in polar temperatures cause CO2 - which makes up 95% of the atmosphere - to condense each winter and form a seasonal "cap" of CO2 ice about 1 to 2 m thick. This cap evaporates away in spring and this cycle causes a 20% variation in the global average surface pressure which was first predicted by Leighton and Murray in 1966 and confirmed by the Viking Landers.
Construction and Destruction of Mountains on Mars
stability. Mars’ sedimentary record is the only known archive of a major planetary habitability transition. No rivers flow on today's Mars, but rovers and orbiters have found >3 Ga-old sedimentary rocks, dry rivers and paleolakes, and aqueous minerals. The nature of the early wet era, the processes that allowed surface liquid water, and the cause of climate deterioration are all unknown.
The "Curiosity" rover is currently exploring the moat encircling a 5km-high sedimentary rock mound in Gale Crater. This moat-and-mound pattern is common in Mars craters and canyons, but its origin is unknown. I will set out the evidence that moats and mounds grew together, shaped by slope winds down the crater and mound flanks, and discuss the implications for liquid water sources on early Mars and for Mars habitability. If time allows, I will discuss ongoing work on connections between time gaps in the Mars sedimentary record (including at Gale Crater) and climate modelling of late bursts of habitability on Mars.
Meg Smith (Graduate Student, University of Washington)
Research Rotation Presentation: Measuring Gas Production by Anoxygenic Photrophic Bacteria
The success of detecting life on another planet is contingent upon our understanding of possible biosignatures. In recent years, research has focused on O2 and O3 as candidates for gaseous biosignatures. But it is not just O2-producers who call Earth home. Microorganisms have dominated Earth for around 80% of its history, and among the most primitive organisms are anoxygenic phototrophs – microbes that use electron donors other than water and do not produce oxygen. Currently, there are no known observable biosignature gases produced by these organisms. During my research rotation, I worked with Dr. Niki Parenteau, at NASA Ames Research Center, to characterize gas production by anoxygenic photrophs using a membrane-inlet mass spectrometer newly-acquired by the Ames group. We initially focused on biogenic S gases that can form from small molecular weight organic compounds produced by the phototrophs combining with sulfide. We calibrated the instrument and then measured gas production from two samples: 1) a culture of purple non-sulfur bacteria and 2) an environmental sample of purple sulfur bacteria that we collected from a sulfidic hot spring in northern California. We observed distinct changes in gas production as we exposed them to oscillating conditions of darkness and light. We conclude the new mass spectrometer looks promising for doing further analysis on gas production from other microbial cultures and natural communities. An unexpected result was that the culture of purple non-sulfur bacteria produced CO2 when exposed to light. The origin of this CO2 remains unknown and deserves further investigation.
Don Brownlee (Professor, University of Washington)
The role of interstellar molecules and large-scale mixing in making habitable planets
The laboratory study of collected comet samples indicate that interstellar solids were largely destroyed during the formation of the solar system and that it is unlikely that interstellar molecules played a significant role in the origin of life on Earth. Nearly all of the rocky components (most of their mass) of the solar system’s original ice-rich planetesimals appear to have formed at high temperatures in hot inner nebula regions by the same processes that made the best preserved nebular materials found in primitive meteorites. The dispersion of isotopic and minor element compositions of comet silicates differs from what is found in meteorites, suggesting that distant solar system bodies contain an averaged mix of inner solar system materials. These materials were derived from a broad range of nebular regions and transported over great distances. The data suggest that comet accretion times were longer than nebular mixing times, in contrast to meteorites that retain regional properties because they accreted faster than solids could be mixed between nebular regions. These results shed new insight into the mystery of why carbon and water are two orders of magnitude less abundant in terrestrial planets than they are in comets, the dominant class of early solar system planetesimal.
Missed the last seminar series? See our archive for abstracts and video recordings of all past talks from 2003 - present.