ALBERT

Description: The primary MER objectives have been successfully completed. The total integration time of all MB measurements exceeds the duration of the primary 90-sols-mission for Spirit's MB spectrometer, and approaches this value for Opportunity's MB spectrometer. Both MB spectrometers continue to accumulate valuable scientific data after three years of operation (data is available for download [13]) The identification of aqueous minerals such as goethite in Gusev crater and jarosite at Meridiani Planum by the MER Mossbauer spectrometers is strong evidence for past water activity at the two landing sites.

Description: The extensive evidence for sulfate deposits on Mars provided by analyses of MER and Mars Express data shows that the sulfur played an essential role in the geochemical cycles of the planet, including reservoirs in the atmosphere, hydro-sphere and geosphere. Overall the data are consistent with a fluvial/lacustrine-evaporative origin of at least some of the sulfate deposits, with mineral precipitation through oversaturation of salty acidic fluids enriched in sulfates. This scenario requires reservoirs of sulfur and associated cations, as well as an acidic and oxidizing hydrochemistry which could be provided by surface and subsurface catching of meteoric waters resulting in the presence of sulfur-bearing gases and steam photochemistry. In this work we suggest a new scenario for the extensive generation of sulfates in Mars based on the observation of seasonal changes in the redox and pH of subsurface waters enriched in sulfur that supply the acidic Mars process analog of Rio Tinto. This model considers the long-term subsurface storage of sulfur during most of Noachian and its release from the late Noachian to Hesperian time through weathering by meteoric fluids that would acidify and oxidize the sulfur bearing compounds stored in the subsurface.

Description: A better understanding of the early impact history of the terrestrial planets has been identified one of the highest priority science goals for solar system exploration. Crystallization ages of impact melt breccias from the Apollo 16 site in the central nearside lunar highlands show a pronounced clustering of ages from 3.75-3.95 Ga, with several impact events being recognized by the association of textural groups and distinct ages. Here we present new geochemical and petrologic data for Apollo 16 crystalline breccia 67955 that document a much older impact event with an age of 4.2 Ga.

Description: The L chondrite Patuxent Range (PAT) 41 91501 is an 8.5-kg unshocked, homogeneous, igneous-textured impact melt that cooled slowly compared to other meteoritic impact melts in a crater floor melt sheet or sub-crater dike. We conducted mineralogical and tomographic studies of previously unstudied mm- to cm-sized metal-sulfide-vesicle assemblages and chronologic studies of the silicate host. Metal-sulfide clasts constitute about 1 vol.%, comprise zoned taenite, troilite and pentlandite, and exhibit a consistent orientation between metal and sulfide and of metal-sulfide contacts. Vesicles make up approximately 2 vol.% and exhibit a similar orientation of long axes. Ar-39-Ar-40 measurements date the time of impact at 4.461 +/- 0.008 Gyr B.P. Cosmogenic noble gases and Be-10 and Al-2l activities suggest a pre-atmospheric radius of 40-60 cm and a cosmic ray exposure age of 25-29 Myr, similar to ages of a cluster of L chondrites. PAT 91501 dates the oldest known impact on the L chondrite parent body. The dominant vesicle-forming gas was S2 (approximately 15-20 ppm), which formed in equilibrium with impact-melted sulfides. The meteorite formed in an impact melt dike beneath a crater, as did other impact melted L chondrites, such as Chico. Cooling and solidification occurred over approximately 2 hours. During this time, approximately 90% of metal and sulfide segregated from the local melt. Remaining metal and sulfide grains oriented themselves in the local gravitational field, a feature nearly unique among meteorites. Many of these metal sulfide grains adhered to vesicles to form aggregates that may have been close to neutrally buoyant. These aggregates would have been carried upward with the residual melt, inhibiting further buoyancy-driven segregation. Although similar processes operated individually in other chondritic impact melts, their interaction produced the unique assemblage observed in PAT 91501.

Description: The concept of a crewed mission to a Near-Earth Object (NEO) has been analyzed in depth in 1989 as part of the Space Exploration Initiative. Since that time two other studies have investigated the possibility of sending similar missions to NEOs. A more recent study has been sponsored by the Advanced Programs Office within NASA's Constellation Program. This study team has representatives from across NASA and is currently examining the feasibility of sending a Crew Exploration Vehicle (CEV) to a near-Earth object (NEO). The ideal mission profile would involve a crew of 2 or 3 astronauts on a 90 to 120 day flight, which would include a 7 to 14 day stay for proximity operations at the target NEO. One of the significant advantages of this type of mission is that it strengthens and validates the foundational infrastructure for the Vision for Space Exploration (VSE) and Exploration Systems Architecture Study (ESAS) in the run up to the lunar sorties at the end of the next decade (approx.2020). Sending a human expedition to a NEO, within the context of the VSE and ESAS, demonstrates the broad utility of the Constellation Program s Orion (CEV) crew capsule and Ares (CLV) launch systems. This mission would be the first human expedition to an interplanetary body outside of the cislunar system. Also, it will help NASA regain crucial operational experience conducting human exploration missions outside of low Earth orbit, which humanity has not attempted in nearly 40 years.

Description: We report results of a recently-completed study of SPIRIT, a candidate NASA Origins Probe. SPIRIT is a spatial and spectral interferometer with an operating wavelength range 25 - 400 microns. SPIRIT will provide sub-arcsecond resolution images and spectra with resolution R = 3000 in a 1 arcmin field of view to accomplish three primary scientific objectives: (1) Learn how planetary systems form from protostellar disks, and how they acquire their chemical organization; (2) Characterize the family of extrasolar planetary systems by imaging the structure in debris disks to understand how and where planets form, and why some planets are ice giants and others are rocky; and (3) Learn how high-redshift galaxies formed and merged to form the present-day population of galaxies. Observations with SPIRIT will be complementary to those of the James Webb Space Telescope and the ground-based Atacama Large Millimeter Array. All three observatories could be operational contemporaneously. SPIRIT will pave the way to the 1 km maximum baseline interferometer known as the Submillimeter Probe of the Evolution of Cosmic Structure (SPECS). In addition to the SPIRIT mission concept, this talk will emphasize the importance of dense u-v plane coverage and describe some of the practical considerations associated with alternative interferometric baseline sampling schemes.

Description: The concept of a crewed mission to a near-Earth object (NEO) has been previously analyzed several times in the past. A more in depth feasibility study has been sponsored by the Advanced Projects Office within NASA's Constellation Program to examine the ability of a Crew Exploration Vehicle (CEV) to support a mission to a NEO. The national mission profile would involve a crew of 2 or 3 astronauts on a 90 to 120 day mission, which would include a 7 to 14 day stay for proximity operations at the target NEO.

Description: The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar UV radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon s surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17, and Luna 24 missions, as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Description: The lunar surface is covered with a thick layer of sub-micron/micron size dust grains formed by meteoritic impact over billions of years. The fine dust grains are levitated and transported on the lunar surface, as indicated by the transient dust clouds observed over the lunar horizon during the Apollo 17 mission. Theoretical models suggest that the dust grains on the lunar surface are charged by the solar ultraviolet (UV) radiation as well as the solar wind. Even without any physical activity, the dust grains are levitated by electrostatic fields and transported away from the surface in the near vacuum environment of the Moon. The current dust charging and levitation models, however, do not fully explain the observed phenomena. Since the abundance of dust on the Moon's surface with its observed adhesive characteristics has the potential of severe impact on human habitat and operations and lifetime of a variety of equipment, it is necessary to investigate the charging properties and the lunar dust phenomena in order to develop appropriate mitigating strategies. Photoelectric emission induced by the solar UV radiation with photon energies higher than the work function (WF) of the grain materials is recognized to be the dominant process for charging of the lunar dust, and requires measurements of the photoelectric yields to determine the charging and equilibrium potentials of individual dust grains. In this paper, we present the first laboratory measurements of the photoelectric efficiencies and yields of individual sub-micron/micron size dust grains selected from sample returns of Apollo 17 and Luna-24 missions as well as similar size dust grains from the JSC-1 simulants. The measurements were made on a laboratory facility based on an electrodynamic balance that permits a variety of experiments to be conducted on individual sub-micron/micron size dust grains in simulated space environments. The photoelectric emission measurements indicate grain size dependence with the yield increasing by an order of magnitude for grains of sub-micron to several micron size radii, at which it reaches asymptotic values. The yield for large size grains is found to be more than an order of magnitude higher than the bulk measurements on lunar fines reported in the literature.

Description: Several physical mechanisms are involved in excavating granular materials beneath a vertical jet of gas. These occur, for example, beneath the exhaust plume of a rocket landing on the soil of the Moon or Mars. A series of experiments and simulations have been performed to provide a detailed view of the complex gas/soil interactions. Measurements have also been taken from the Apollo lunar landing videos and from photographs of the resulting terrain, and these help to demonstrate how the interactions extrapolate into the lunar environment. It is important to understand these processes at a fundamental level to support the ongoing design of higher-fidelity numerical simulations and larger-scale experiments. These are needed to enable future lunar exploration wherein multiple hardware assets will be placed on the Moon within short distances of one another. The high-velocity spray of soil from landing spacecraft must be accurately predicted and controlled lest it erosively damage the surrounding hardware.