P52A-01
Geologically agnostic approaches to constraining the ice shell thickness of Europa.
Working from the Galileo magnetometer results, we have set new constraints on the ice shell thickness and salinity of the Europan ocean [1]. The induced magnetic field response of Europa to the time-varying component of the background Jovian magnetic field necessitates a near-perfect conducting layer within approximately 10 km of the surface, with an optimal fit of 4 km thickness. Achieving the empirically constrained amplitude response [2] requires near-saturation salt concentrations in an ocean beneath a thin (<10 km) ice shell. If the amplitude response is determined to be lower than A = 0.97 ± 0.02, e.g. in the range of A = 0.90, then the salt concentration can be lowered by nearly an order of magnitude or the ice shell thickness can be increased by a factor of a few. Continuing analysis of the magnetometer data indicates that the amplitude may indeed be lower than reported by Schilling et al. (2004), (Schilling, Khurana, pers. comm.). Geochemically, we find that achieving near-saturation with either magnesium sulfate or sodium chloride is implausible [3]. This contradicts early geochemical work for Europa [4] but is consistent with other more recent models [5]. Geochemical models can support a few to a few tens of grams of salt per kg of water, yielding ocean conductivities of ~0.5-6 S/m. For an induced amplitude response of A > 0.9, these geochemical constraints require the ice shell to be < 30 km thick. For higher values of A, or for lower values on salinity, the ice thickness must be decreased. The ~5-10 g salt per kg models of [5, 6] will not work unless the amplitude is < 0.9 or the ice shell is < 10 km thick. [1] Hand, K.P. & Chyba, C.F. (2007) Icarus. [2] Schilling et al., (2004) JGR. [3] Hand (2007) PhD Thesis. [4] Kargel et al., (2000) Icarus [5] Zolotov and Shock, (2001) JGR [6] Zolotov et al. (2006) LPSC.
P52A-02 INVITED
The Arctic Gakkel Vents (AGAVE) Expedition: Technology Development and the Search for Deep-Sea Hydrothermal Vent Fields Under the Arctic Ice Cap
Deep-sea hydrothermal fields on the Gakkel Ridge beneath the Arctic ice cap provide perhaps the best terrestrial analogue for volcanically-hosted chemosynthetic biological communities that may exist beneath the ice-covered ocean of Europa. In both cases the key enabling technologies are robotic (untethered) vehicles that can swim freely under the ice and the supporting hardware and software. The development of robotic technology for deep- sea research beneath ice-covered oceans thus has relevance to both polar oceanography and future astrobiological missions to Europa. These considerations motivated a technology development effort under the auspices of NASA's ASTEP program and NSF's Office of Polar Programs that culminated in the AGAVE expedition aboard the icebreaker Oden from July 1 - August 10, 2007. The scientific objective was to study hydrothermal processes on the Gakkel Ridge, which is a key target for global studies of deep-sea vent fields. We developed two new autonomous underwater vehicles (AUVs) for the project, and deployed them to search for vent fields beneath the ice. We conducted eight AUV missions (four to completion) during the 40-day long expedition, which also included ship-based bathymetric surveys, CTD/rosette water column surveys, and wireline photographic and sampling surveys of remote sections of the Gakkel Ridge. The AUV missions, which lasted 16 hours on average and achieved operational depths of 4200 meters, returned sensor data that showed clear evidence of hydrothermal venting, but for a combination of technical reasons and time constraints, the AUVs did not ultimately return images of deep-sea vent fields. Nevertheless we used our wireline system to obtain images and samples of extensive microbial mats that covered fresh volcanic surfaces on a newly discovered set of volcanoes. The microbes appear to be living in regions where reducing and slightly warm fluids are seeping through cracks in the fresh volcanic terrain. These discoveries shed new light on the nature of volcanic and hydrothermal processes in the Arctic basin, and also demonstrate the importance of new technologies for advancing science beneath ice-covered oceans. Operationally, the AUV missions pushed the envelope of deep-sea technology. The recoveries were particularly difficult as it was necessary to have the vehicle find small pools of open water next to the ship, but in some cases the ice was in a state of regional compression such that no open water could be found or created. In these cases a well-calibrated, ship-based, short-baseline acoustic system was essential for successful vehicle recoveries. In all we were able to achieve a variety of operational and technological advances that provide stepping stones for future under-ice robotic missions, both on Earth and perhaps eventually on Europa.
P52A-03
Europan Ocean Sulfate Chemistry To 700 MPa From -20 to 100 oC
The scale height of Europa's ocean is comparable to that of Earth's atmosphere. Pressure at the bottom of Europa's ocean is as much as twice that at the greatest depth in Earth's. Subtle effects of pressure on aqueous solution chemistry at these depths may have profound implications for fluid dynamics and mass transport, which may be observable by the next Europa mission. In this context, we present an equation of state for aqueous MgSO4, derived from speeds of sound obtained by the method of impulsive stimulated scattering. Measurements were made at 0, 0.5103, 0.9965, 1.506 and 2.014 m to 700 MPa from -20 to 100 oC. Few thermodynamic measurements have been made to such high pressures and low temperatures. This range is relevant to Europa's ocean and possibly other oceans in the outer Solar System. Preliminary analyses indicate densities measured above 100 MPa (equivalent to pressure at the bottom of the Marianas Trench in Earth's ocean) are misfit by extrapolation from previously published values by as much as ten percent. http://earthweb.ess.washington.edu/~svance/ISIS_AGU2007
P52A-04
DEPTHX to Zacaton - Field Tests of a Europa Lander Third Stage Prototype
The NASA Deep Phreatic Thermal Explorer (DEPTHX) project led to the successful development of a fully autonomous underwater vehicle intended as a prototype of the Europa lander third stage that will search for microbial life beneath the ice cap of that Jovian moon. DEPTHX had two principal objectives: First, to develop and test in an appropriate environment the ability for an un-tethered robot to explore into unknown 3D territory, to make a map of what it sees, and to use that map to return home; and second, to demonstrate that science autonomy behaviors can identify likely zones for the existence of microbial life, to command an autonomous maneuvering platform to move to those locations, conduct localized searches, and to autonomously collect microbial life in an aqueous environment. The concept and prototypes were tested in the deep hydrothermal cenote of Zacatón, Mexico. In this presentation we summarize the final vehicle architecture and control systems approach to autonomous exploration in fully 3D environments in which apriori knowledge of the environment is non-extant and for which there exists no external navigation system. The results of the field work at Cenote Zacaton and the related feature known as Cenote La Pilita will be presented including the February 5, 2007 mission during which DEPTHX became the first fully autonomous cave exploring robot. http://www.stoneaerospace.com
P52A-05 INVITED
Environmentally Non-Disturbing Under-ice Robotic ANtarctiC Explorer (ENDURANCE)
Permanently ice-covered liquid water environments are among the leading candidate sites for finding evidence of extant life elsewhere in our solar system (e.g. on Europa and other Galiean satellites, and possibly in subglacial lakes on Mars). In order to have the proper tools and strategies for exploring the extant ice-covered planetary environments, we are developing an autonomous underwater vehicle (AUV) capable of generating for the first time 3-D biogeochemical datasets in the extreme environment of perennially ice-covered Antarctic dry valley lakes. The ENDURANCE (Environmentally Non-Disturbing Under-ice Robotic ANtarctic Explorer) will map the under-ice lake dimensions of West Lake Bonney in the McMurdo Dry Valleys, and be equipped to measure a comprehensive suite of physical and biogeochemical indices in the water column, as well as Raman Spectrometry of the water column and benthos. The AUV is being specifically designed to minimize impact on the environment it is working in. This is primarily to meet strict Antarctic environmental protocols, but will also be useful for planetary protection and improved science in the future. We will carry out two Antarctic field seasons (in concert with our NSF-funded Long Term Ecological Research) and test two central hypotheses: H1: The low kinetic energy of the system (diffusion dominates the spatial transport of constituents) produces an ecosystem and ecosystem limits that vary significantly in three dimensions. H2: The whole-lake physical and biogeochemical structure remains static from year to year The talk will provide an overview of the ENDURANCE project and an update on the AUV development at the time of presentation.
P52A-06
Lake Vostok: An earthly analogue for the geomicrobiology on Europa
The recent discovery of more than 150 subglacial lakes beneath the Antarctic ice sheet has important implications in our search for liquid water and associated life on other icy worlds. The largest of these lakes is Lake Vostok, which has a surface area of 14000 square km and a depth of 1000 m, making it one of the largest lakes on Earth. Although we have yet to sample directly the liquid water from any of the Antarctic subglacial lakes, refrozen lakewater (accretion ice) has been sampled just above the surface of Lake Vostok. Genomic and geochemical analysis of this ice reveals that the surface lake water supports a microbial assemblage with a density approaching 1000 cells per milliliter. Sequencing and phylogenetic analysis of the 900 to 1000 base pair small subunit rRNA gene sequences obtained revealed a low diversity of clones that classify within the beta, gamma and delta subdivisions of the phylum Proteobacteria. Nearest phylogenetic neighbor analysis of these gene sequences imply that the lake contains an aerobic and anaerobic consortium of bacteria with metabolisms dedicated to iron and sulfur respiration or oxidation indicating that these metals play a role in the bioenergetics of microorganisms that occur in Lake Vostok. Sequence analysis further revealed that heterotrophic life in the lake can be sustained by chemolithotrophic production of new carbon supplemented by dissolved organic carbon released from the overlying ice sheet. Data obtained from orbiters have revealed that a deep ocean of liquid water lies under a thick chaotic ice cover on Europa where organic matter derived from comets and oxidants provided by radiation from Jupiter's magnetosphere may provide a habitat for life and a reservoir of endogenous and exogenous substances much like we observe in Lake Vostok. Future studies of Antarctic subglacial lake environments will play a crucial role in our understanding of life on Europa and other frozen worlds.
P52A-07
Guidelines to Avoid Biocontamination of Antarctic Subglacial Aquatic Environments: Forward Contamination Concerns, Environmental Management and Scientific Stewardship of Icy analogue environments
For more than a decade, scientists and space mission planners have recognized the importance of collaborative information exchange with the Antarctic research community to address their many shared exploration challenges, from drilling methods, remote sample collection, and data interpretation, to concerns about cross contamination that could adversely impact both the environment and interpretation of scientific data. Another shared concern exists in the regulatory realm; both the Antarctic and outer space environments are subject to separate international treaties that impose regulatory controls and oversight with serious implications for exploration planning. In recent years, both communities have faced the need to adjust their regulatory controls in light of fast-paced advances in scientific understanding of extreme environments, particularly related to potential microbial life. Both communities have sought and received advice from the National Research Council (NRC) through studies that suggested ways to update their respective oversight and regulatory systems while allowing for continued scientific exploration. A recently completed NRC study "Exploration of Antarctic Subglacial Aquatic Environments: Environmental and Scientific Stewardship" provided a suite of recommendations to address1) ‘cleanliness' levels necessary for equipment and devices used in exploration of subglacial aquatic environments, as well as 2) the scientific basis for contamination standards, and 3) the steps for defining an overall exploration strategy conducive to sound environmental management and scientific stewardship. This talk will present the findings of the recent multinational NRC study, which is likely to translate into useful information for analogue studies that proceed to test techniques and capabilities for exploring an Europan ocean, other icy celestial locations, and related science targets on Earth. As the science and exploration of subglacial environments grows beyond its infancy, the initial methodologies and protocols will undoubtedly continue to need further development and regular revision— making continued collaboration and communication between the polar and space communities mutually beneficial and advisable. NRC Study Committee members: 1 John E. Hobbie (Chair), Marine Biological Laboratory, Woods Hole, Massachusetts; 2 Amy Baker, Technical Administrative Services, Littleton, Colorado; 3 Garry Clarke, The University of British Columbia, Vancouver, Canada; 4 Peter T. Doran, University of Illinois at Chicago, Earth and Environmental Sciences; 5 David Karl, University of Hawaii at Manoa, School of Ocean and Earth Science, Honolulu; 6 Barbara Methé, The Institute for Genomic Research, Rockville, Maryland; 7 Heinz Miller, Alfred-Wegener-Institute for Polar and Marine Research, Germany; 8 Samuel B. Mukasa, University of Michigan, Ann Arbor; 9 Margaret Race, SETI Institute, Mountain View, California; 10 Warwick Vincent, Département de Biologie, Université Laval, Québec, Canada; 11 David Walton, British Antarctic Survey, Cambridge, United Kingdom; 12 James White, University of Colorado, Boulder, 13 Maria Uhle (Study Director), National Research Council.
P52A-08 INVITED
Europa Explorer: A Mission to Explore Europa and Investigate Its Habitability
Europa is the astrobiological archetype for icy satellite habitability, with a warm, salty, water ocean with plausible chemical energy sources. It is also a geophysical wonderland of interrelated ice shell processes that are intimately related to the ocean and tides, and of complex interactions among its interior, surface, atmosphere, and particles and fields environments. In 2007, NASA commissioned a study of a flagship-class mission to Europa, with the aim of launching as early as 2015. The difficulty of this type of mission, primarily due to the propulsive requirements and Jupiter's trapped radiation, led to many previous studies which investigated various approaches to meeting the science objectives. The Europa Explorer is a mature orbiter concept to explore Europa and investigate its habitability, fulfilling objectives laid out by the National Research Council's Planetary Science Decadal Survey. The mission examines Europa's ocean, ice shell, chemistry, geology, external environment, and neighborhood. With a nominal launch in June 2015, the flight system arrives at Jupiter in 6 years using a Venus- Earth-Earth Gravity Assist trajectory. It would orbit Jupiter for 2 years using gravity assists of the icy Galilean satellites to lower its energy, providing the opportunity for significant Jupiter system science. It would then enter Europa orbit at an altitude of 100-200 km, where it would perform science investigations for 1 year. A campaign- based operations scenario has been developed which permits return of 5.4 Tbits of science data beginning in July 2021, and emphasizing the highest priority Europa science objectives early in the orbital phase of the mission. The baseline mission concept includes 11 instruments that address high-priority investigations while providing the flexibility to respond to discoveries. A less ambitious mission has also been evaluated which has 8 instruments and returns about a third of the data with 6 months of orbital operations at Europa. The radiation design approach has been independently reviewed and validated, and a statistical lifetime prediction method has been developed. Past technology investments have reduced mission risk, making the Europa Explorer mission ready to move forward in order to address the high-priority astrobiological and geophysical objectives outlined by the Decadal Survey.