TBA
December 02, 2016 12:00p - 2:30p
TBA
Institute for Planets and Life
Space Telescope Science Institute and Johns Hopkins University
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: http://www.stsci.edu/institute/smo/ipl/abstracts
Äàòà èçìåíåíèÿ: Unknown Äàòà èíäåêñèðîâàíèÿ: Sun Apr 10 17:30:45 2016 Êîäèðîâêà: Ïîèñêîâûå ñëîâà: mercury program |
Space Telescope Science Institute and Johns Hopkins University
December 02, 2016 12:00p - 2:30p
TBA
November 04, 2016 12:00p - 2:30p
TBA.
October 07, 2016 12:00p - 2:30p
TBA
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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.
Webcast: View the Lecture Webcast
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