P51B-0483
Lunar Internal Structure From Reflected and Converted Core Phases
Seismic constraints on lunar structure come primarily from the analysis of surface impacts and both shallow and deep moonquakes. These have been used to estimate the thickness of the lunar crust, and the structure of the mantle down to approximately 1000 km depth. However, a direct seismic constraint on the size of the lunar core is difficult to obtain due to several factors. Core phases from naturally-occurring deep moonquakes are not observed on seismograms from the Apollo instruments, in part due to the strong scattering of seismic energy in the lunar crust. The scattering coda associated with the main P and S arrivals prohibit the immediate identification of secondary phases, even on stacked seismograms. Depending on the choice of lunar structure model, a variety of phase arrivals from deep moonquakes could theoretically be detected at the four Apollo seismic stations. We attempt to determine whether further manipulation of the Apollo seismic data will permit the identification of core phases. We will employ a time-domain method of resolving secondary phase arrivals from the Apollo data, using stacked deep moonquake seismograms which include recently discovered additional events. Because the P-wave coda associated with most deep moonquakes is very long, later arrivals are masked. Deconvolution of a given moonquake signal by its P-wave arrival may therefore enhance arrivals from reflected (e.g. PcP) and converted (e.g. PKP) core phases. These can be compared to travel times and amplitudes predicted from ray theory in order to constrain the structure of the lunar core. In addition, we asses the likelihood that a future lunar seismometer could detect core phases. The seismometer currently in development for the ESA mission ExoMars, if modified for use on the lunar surface, would permit measurements 100 times more sensitive than the Apollo instruments. For a given core radius, we can determine which locations on the lunar surface would receive core phases from the known distribution of deep moonquake sources. A seismic station at the proposed location of the south pole lunar base could detect both PcP and PKP from many deep source regions, in addition to ScS, SKS, ScP, PcS, and both the direct P and S phases.
P51B-0484
Periodic changes in shallow lunat crust caused by Sun's heating and thermal diffusivity near the surface
Analysis of Apollo 17 data (continuous data from 1976 to 1977) by the cross-correlation approach for seismic noise led us to two new discoveries, one related to the source of noise and the other on the periodic changes in seismic parameters due to extreme temperature changes near the surface. It has been shown previously by Larose et al. (2005) that Green's functions, dominated by Rayleigh waves, can be retrieved from cross-correlation of seismic noise in Apollo 17 data. We first confirmed their correlation results and further analyzed the details in GreenA?qfs functions. The first discovery is that the sources of noise that lead to construction of Green's functions are (most likely) thermal moonquakes. This is suggested in the Rayleigh-wave observations that show diurnal variation (29.5 days) in amplitudes, but one can directly confirm a correlation between the statistics of thermal moonquakes and Rayleigh wave amplitudes. This is in contrast to the terrestrial case where ocean-generated seismic noise plays a critical role in the cross-correlation approach. This has implications for future planetary seismology as many planets lack oceans but may have thermal quakes caused by drastic temperature changes near the surface. Second, diurnal temporal variations in group velocity are detected, showing a strong correlation with the temporal variation of lunar surface temperature. This can be explained by the Sun's thermal effects which cause changes in density and seismic velocities near the surface. These effects are measurable on the moon since surface temperature changes as much as 270 K within the diurnal period. Depending on the thermal diffusivity of the medium, the depth extent of this thermal effect varies considerably. Inversion for thermal diffusivity using the changes in group velocity dispersion resulted in an estimate 10**(-7) (m**2/s) for the upper few meters.
P51B-0485
Polar Lunar Regions: Exploiting Natural and Augmented Thermal Environments
In polar regions of the Moon, there are areas within craters that are permanently shadowed from solar illumination, which can reach temperatures of 100K or less. These regions could serve as cold traps, capturing ice and other volatile compounds. These potential ice stores have many applications for lunar exploration. Within double-shaded craters, even colder regions exist, with temperatures never exceeding 50K in many cases. Temperatures observed in theses regions suggest that they could enable equivalent liquid nitrogen cryogenic functions. These permanently shaded polar craters also offer unprecedented high vacuum cryogenic environments, which in their current state could support cryogenic applications. The unique conditions at the lunar poles, besides ice stores, harbor an environment that provides an opportunity to reduce the power, weight and total mass that needs to be carried from the Earth to the moon for lunar exploration and research. Reducing the heat flux of geothermal, black body radiation can have significant impacts on the achievable temperature. With a few man-made augmentations, permanently shaded craters located near the lunar poles achieve temperatures even lower than those that naturally exist there. Our analysis reveals that lightweight thermal shielding, within shaded craters, could create an environment several Kelvin above absolute zero. The temperature ranges of naturally shaded craters and thermally augmented ones could enable the long-term storage of most gases, low temperature superconductors for large magnetic fields, devices and advanced high speed computing instruments. Augmenting thermal conditions in these craters could then be used as a basis for the development of an advanced thermal management architecture that would support a wide variety of cryogenically based applications. Lunar exploration and habitation capabilities would significantly benefit if permanently shaded craters, augmented with thermal shielding, were to be used to facilitate the operation of near absolute zero instruments, including wide variety of cryogenically based propulsion, energy, communication, sensing and computing devices. Potentially, the required burden of carrying massive life-supporting components from the Earth to the moon for lunar exploration and research could be reduced.
P51B-0486
Modeling Lunar Borehole Temperature in order to Reconstruct Historical Total Solar Irradiance and Estimate Surface Temperature in Permanently Shadowed Regions
The Moon is an ideal place to reconstruct historical total solar irradiance (TSI). With undisturbed lunar surface albedo and the very low thermal diffusivity of lunar regolith, changes in solar input lead to changes in lunar surface temperature that diffuse downward to be recorded in the temperature profile in the near-surface layer. Using regolith thermal properties from Apollo, we model the heat transfer in the regolith layer, and compare modeled surface temperature to Apollo observations to check model performance. Using as alternative input scenarios two reconstructed TSI time series from 1610 to 2000 (Lean, 2000; Wang, Lean, and Sheeley 2005), we conclude that the two scenarios can be distinguished by detectable differences in regolith temperature, with the peak difference of about 10 mK occuring at a depth of about 10 m (Miyahara et al., 2007). The possibility that water ice exists in permanently shadowed areas near the lunar poles (Nozette et al., 1997; Spudis et al, 1998), makes it of interest to estimate surface temperature in such dark regions. "Turning off" the Sun in our time dependent model, we found it would take several hundred years for the surface temperature to drop from ~~100K immediately after sunset down to a nearly constant equilibrium temperature of about 24~~38 K, with the range determined by the range of possible input from Earth, from 0 W/m2 without Earth visible, up to about 0.1 W/m2 at maximum Earth phase. A simple equilibrium model (e.g., Huang 2007) is inappropriate to relate the Apollo-observed nighttime temperature to Earth's radiation budget, given the long multi- centennial time scale needed for equilibration of the lunar surface layer after sunset. Although our results provide the key mechanisms for reconstructing historical TSI, further research is required to account for topography of lunar surfaces, and new measurements of regolith thermal properties will also be needed once a new base of operations is established. References Huang, S., (2007), Surface Temperatures at the Nearside of the Moon as a Record of the Radiation Budget of Earth's Climate System, Advances in Space Research, doi:10.1016/j.asr.2007.04.093. Lean, J., Geophys. Res. Lett., (2000), 27(16), 2425-2428. Miyahara, H., G. Wen, R. F. Cahalan, and A. Ohmura, (2007), Deriving Historical Total Solar Irradiance from Lunar Borehole Temperatures, submitted to Geophy. Res. Lett. Nozette, S., E. M. Shoemaker, P. D. Spudis, and C. L. Lichtenberg, The possibility of ice on the Moon, Science, 278, 144-145, 1997. Spudis, P.D., T. Cook, M. Robinson, B. Bussey, and B. Fessler, Topography of the southe polar region from Clementine stereo imaging, New views of the Moon, Integrated remotely sensed, geophysical, and sample datasets, Lunar Planet. Inst., [CD-ROM], abstract 6010, 1998. Wang, Y. M., J. L. Lean and N. R. Sheeley (2005), Astrophys. J., 625, 522-538.
P51B-0487
A Small Geodesy Surface Package for Future Lunar Robotic Missions
We propose to deploy small (2-3 kg) Lunar geodesy packages on the Moon's surface, consisting of an optical Laser receiver, a small retroreflector, as well as a radio beacon. The optical receiver will maintain Earth pointing through the Lunar libration cycles and record arrival times of Laser shots from Earth. Judging from the photon budget for a 50 mJ pulse Laser, most of the existing more than 30 ILRS (International Laser Ranging Service) stations could participate in the experiment and produce large numbers of range measurements at high accuracy and unbiased temporal coverage. The light-weight 0.5 sqm retroreflector will be adequate for direct ranging measurements using the classic Lunar Laser Ranging stations. The simultaneous acquisition of data from the Laser receiver on the Moon and reflected Laser shots on Earth will allow us to calibrate the onboard clock. A small radio source shall be deployed within the package, for tracking by VLBI stations. The experience from the past 38 years of Apollo Lunar Laser Ranging suggests that there is enormous science potential in ranging data to further our understanding of the Moon's internal structure, the dynamics of the Earth-Moon system and fundamental physics. For example, from the Moon's tidal response, inferences can be made on a solid or liquid Lunar core and its size and oblateness. In addition, parameters from gravitational physics, e.g., the time-stability of the gravitational "constant", or the strong equivalence principle (Nordtvedt-effect) could be modeled with vastly improved accuracy. While the position of the Laser receiver will define an important anchor point in the lunar-fixed coordinate system, the radio transmitter will firmly tie the dynamical reference frame of the Lunar orbit into the quasi-inertial kinematic reference frame of Quasar coordinates for insights into the Moon's orbital behavior to as yet unknown frontiers.
P51B-0488
A Design for an Integrated Lunar Geophysics Instrument Package (L-GIP)
The development of the Lunar Geophysics Instrument Package (L-GIP) is international collaborative investigation to record geophysical measurements on the surface of the Moon over several years (>6) and transmit the data back to Earth either directly, or via a surface or orbital relay asset. The L-GIP will include a seismometer, a heat flow probe, and a magnetometer. Each instrument that forms the L-GIP is relatively mature and was/is a payload on past, current or future planetary missions. However, the modifications to these (for integrating into one deployable unit), along with the required architecture, are needed. Significant trade studies include how to operate in an adverse thermal regime (transition between lunar night/day), long-lived power supply options, networking of different L-GIPs, defining the best design of heat flow probe to achieve the sciences goals (i.e., designs from Apollo, Lunar-A penetrator, and Rosetta missions), inclusion (or not) of a solar wind detector for the magnetic studies, and deployment strategies. The L-GIP instruments have been chosen because their individual data sets will address several unanswered scientific questions regarding the lunar interior and lunar evolution, as well as provide valuable data for exploration. The as yet unanswered science questions include: What is the composition and size of the lunar core? What is the internal structure of the whole Moon? What is the global thermal budget of the Moon and how has this impacted its evolution? Did the early Moon have a dynamo and if so, when did it start and when did it stop? Unanswered exploration questions include: What is the nature of ground movement in response to the large (body wave magnitude 5 or greater) Moonquakes that are known to occur? Do meteoroid impacts fall more in one area than another on the Moon? A global network of L-GIP instruments strategically placed around the Moon and operational for 6+ years will go a long way to answering such questions. The fundamental importance of the L-GIP is that the dataset from one instrument will enhance the datasets from the others. This is vital because using combined data types together in cooperative inversion approaches can be effective in limiting the number of acceptable interpretations. For example, magnetic data can provide good constraints on near-surface density, especially if combined with gravity data (a higher resolution data set of which will become available with the Japanese SELENE mission). The seismic models tend to resolve horizontal layers well, while magnetic approaches resolve lateral variations or vertical interfaces in subsurface magnetic susceptibility (and density if gravity data again are available). Heat flow data can provide additional lateral and sometimes (coarse) vertical property constraints, but also provide key model constraints for seismic (velocity) and density models. So, by combining these instruments in the L-GIP the datasets thus generated will dramatically lessen ambiĴguities in our understanding of the lunar interior.
P51B-0489
Highly Oxidizing Surface Radicals in Lunar Dust
Lunar rocks are generally believed to be very "dry" with little or no evidence for hydroxyl as indicators of traces of dissolved H2O. The absence of hydroxyl, however, is not a sure sign of the absence of dissolved H2O. The reason is that hydroxyl pairs in the structure of host minerals, O3X-OH HO-XO3, with X=Si4+, Al3+ etc., tend to undergo an electronic rearrangement (redox conversion) in the course of which two oxygen anions are oxidized from the 2- to the 1- valence, forming a peroxy link, O3X-OO-XO3, plus an H2 molecule. If the H2 molecules diffuse out (which they are expected to do from lunar rocks and lunar fines over the course of 4 Gyrs), the peroxy links remain as the only "memory" of a former solute H2O content. Hard UV causes peroxy links to dissociate. In the process an electron from a neighboring O2 jumps into the broken peroxy bond. This is equivalent to forming an O, e.g. a defect electron in the oxygen anion sublattice. Such defect electrons, also known as positive holes or pholes for short, represent highly mobile charge carriers. When trapped at the surface of dust grains, these charge carriers turn into highly reactive, highly oxidizing O radicals, which are of concern because of their toxicity when lunar dust is inhaled by astronauts. We propose a device to measure the UV-activation of peroxy links by dusting lunar fines onto a polyethylene base plate with Au electrodes sputtered onto both ends and an ammeter connecting the two electrodes. One end of the dust layer will be exposed to the ambient UV radiation, while the remainder will be shaded. During the lunar night no current is expected to flow between the two Au electrodes. During passage through the night-day terminator, a current is expected to flow between the Au electrodes carried by defect electrons activated in the irradiated portion of the dust layer. Such a current would be an indicator that lunar fines and, by implication, lunar rocks contain peroxy links as a memory of a former solute H2O content.
P51B-0490
Lunar Exploration and the Speed of Light
A "Hot Young Solution to Faint Sun Paradox" earlier offered hints that the speed of light may be slowing. Human exploration of the Moon has provided a further test. The Lunar Laser Ranging Experiment from 1969 measures the Moon's recession at 3.84 cm/yr, anomalously high. Geology and paleontology indicate that lunar recession has been just 2.9 cm/yr (Bills and Ray, 1999). A Theory of Space/Time proposes that speed of light c is related to age t of the Universe by GM=tc3. For a Universe of 13.7 Ga, predicted c change is 1 in 41.1 Ga. Multiplied by the Moon's distance of 384,402 km, the Moon will appear to recede an additional 0.935 cm/yr. The anomaly in lunar recession is precisely accounted for, indicating that c changes to this day. Change in c is precisely corroborated by Type Ia supernova redshifts. Earth's climate record, when compared to solar models, has provided further corroboration. In summary, data from three truly independent sources indicates that c has changed as predicted. Future lunar exploration with more advanced equipment will doubtless lead to more surprises. http://www-conf.slac.stanford.edu/einstein/talks/aspauthor2004_3.pdf
P51B-0491
Electrostatic Levitation of Lunar Dust: Preliminary Experimental Observations
A lunar dust laboratory has been established in the Space Science Division at NASA Ames to evaluate fundamental electrostatic processes at the Moon's surface. Photoelectric charging, triboelectric charging, and interactions of these processes are investigated for dust-size materials. An electric field simulating the solar- plasma induced E-field of the lunar surface has been created with parallel charged capacitance plates. The field is linear, but field-shaping to create lunar-like exponentially decaying E-fields will be conducted in the near future. Preliminary tests of dust tribocharging have been conducted using a vibrating base plate within the electric field and have produced electrostatic levitation of 1.6 micron diameter silicate particles. We were able to achieve levitation in a modest vacuum environment (1.7 Torr) with the particles charged to approximately 15 percent of the Gaussian limit (defined as 2.64 E-5 C/m-2 for atmospheric air) at a threshold field strength of 2250 V/m. This charging corresponds to only a few hundred (negative) charges per particle; the field strength drops to 375 V/m when gravitationally scaled for the Moon, while dust tribocharging to greater than 100 percent of the Gaussian limit would be possible in the ultra high vacuum environment on the Moon and result in even lower threshold field strengths. We conclude therefore, that anthropogenic disturbance of lunar dust (as a result of NASA's proposed base construction, mining, vehicle motion, etc) could potentially pollute the lunar environment with levitated dust and severely impair scientific experiments requiring a pristine lunar exosphere.
P51B-0492
Thermal Effects of Lunar Surface Roughness: Application for the 2008 LRO Diviner Lunar Radiometer Experiment
It is well known that surface roughness affects spectral slope in the infrared. For the first time, we applied a three-dimensional thermal model to a high resolution lunar topography map to study the effects of surface roughness on lunar thermal emission spectra. We applied a numerical instrument model of the upcoming Diviner Lunar Radiometer Experiment (DLRE) to simulate the expected instrument response to surface roughness variations. The Diviner Lunar Radiometer Experiment (DLRE) will launch in late 2008 onboard the Lunar Reconnaissance Orbiter (LRO). DLRE is a nine-channel radiometer designed to study the thermal and petrologic properties of the lunar surface. DLRE has two solar channels (0.3-3.0 μm high/low sensitivity), three mid-infrared petrology channels (7.55-8.05, 8.10-8.40 8.40-8.70 μm), and four thermal infrared channels (12.5-25, 25-50, 50-100, and 100-200 μm). The topographic data we used was selected from a USGS Hadley Rille DEM (from Apollo 15 Panoramic Camera data) with 10 m resolution (M. Rosiek; personal communication). To remove large scale topographic features, we applied a 200 x 200 pixel boxcar high-pass filter to a relatively flat portion of the DEM. This "flattened" surface roughness map served as the basis for much of this study. We also examined the unaltered topography. Surface temperatures were calculated using a three-dimensional ray tracing thermal model. We created temperature maps at numerous solar incidence angles with nadir viewing geometry. A DLRE instrument model, which includes filter spectral responses and detector fields of view, was applied to the high resolution temperature maps. We studied both the thermal and petrologic effects of surface roughness. For the thermal study, the output of the optics model is a filter specific temperature, scaled to a DLRE footprint of < 500 m. For the petrologic study, we examined the effect of the surface roughness induced spectral slope on the DLRE's ability to locate the Christiansen Feature, which is a good compositional indicator. With multiple thermal infrared channels over a wide spectral range, DLRE will be well suited to measure temperature variations due to surface roughness. Any necessary compensation (e.g. correction for spectral slope) to the mid-infrared petrology data will be performed.
P51B-0493
Grain Size Effects (5-63μm) of the UV-VIS-NIR Spectra of Ilmenite-Bearing Assemblages: Implications for Mapping TiO2 in the Lunar Maria
Fine-grained particles (≤60μm) dominate the particle size distributions of many planetary surfaces. Systematic studies of particle size effects within the fine fraction have typically concentrated on transparent silicate minerals [1,2]. We have acquired a synthetic powdered ilmenite sample from Sigma-Alrich and verified the composition via X-ray diffraction and Mössbauer spectroscopy. The sample was separated into six size fractions between 5 and 63μm using ultrasonic sieving techniques (Gilson Company). Reflectance spectra, taken at RELAB, between 0.3 and 2.5μm show systematic changes in spectral contrast with particle size. A long-standing goal of the lunar science community has been the remote mapping of TiO2 abundance on the lunar surface to enable detailed studies of lunar crustal composition, surface volcanism and temporal and spatial variations in mantle composition. Returned lunar regolith samples have large variations in TiO2 abundance (0-10wt%), dominantly in the opaque oxide mineral ilmenite (FeTiO3). There is a correlation between TiO2 abundance and the ratio of ultraviolet (UV) to visible (VIS) reflectance of lunar soils but the accuracy and universal applicability of the correlation persists. Gillis-Davis and coworkers [3], demonstrated the effect of ilmenite grain size on the TiO2-UVVIS color correlation of modeled mixtures of ilmenite with low-Ti lunar mare soil for variations in ilmenite grain size from the rest of the lunar soil. They found that reducing the modeled grain size of ilmenite increased its cross sectional area and thus its spectral effectiveness. Utilizing the new ilmenite size separates we present the single scattering albedo as a function of particle size (5-63μm) in the wavelength range 0.3-2.5μm. These data can be used to improve modeled mixtures of ilmenite as a function of grain size. We show that spectral variations in ilmenite with grain size introduces scatter into the TiO2-UVVIS color correlation even if the grain size of the ilmenite is the same as the lunar soil in which it is contained. We also show that the spectral changes in ilmenite due to grain sizes will temper the magnitude of the grain size effects demonstrated by Gillis-Davis et al. [3] and makes it less likely that the UVVIS-TiO2 correlation can be explained by ilmenite alone. Grain size effects cannot explain the full range of TiO2 variability but do introduce significant scatter in UVVIS - TiO2 correlation. These findings emphasize the need to understand secondary controls on the UVVIS color of lunar soils in order to yield accurate TiO2 estimates. [1] Mustard and Hayes, Icarus, 1997; [2] Adams and Felice, JGR, 1967; [3] Gillis-Davis et al., GCA, 2006.
P51B-0494
Mineralogy of the Moon by multiple endmember spectral unmixing of Clementine UVVIS and NIR data
Global observations of the Moon have been made by the imaging spectrometers onboard the Clementine spacecraft in 1994 [1]. These data have 5 channels in the Ultra-Violet Visible (UVVIS) in the range 450-1000 nm and 6 in the Near Infra-Red (NIR) in the range 1100-2780 nm. UVVIS global mosaic has been widely used in spectral analysis (e.g. [2, 3]). Calibration issues in the NIR data did not favor spectral studies using the full wavelength range [4]. Only a few analyses have been made in the NIR using different calibration approaches (e.g. [5]), despite potential valuable information to discriminate more minerals. A new calibration has finally been applied on the NIR [6, 7] and a mosaic calibrated in Bidirectional Reflectance (BRDF) has been released [8]. Quantitative mapping of minerals is possible using Clementine data 1) by converting BRDF into single scattering albedo [9, 10] and 2) by performing spectral linear unmixing [11]. Multiple-Endmember Spectral Mixture Analysis (MESMA, [12]) has been successfully applied with UVVIS data [11]. This method allows spectral unmixing to be calculated using a limited number of components, even if a lot more spectral endmembers are available in the reference spectral library. We have analyzed newly calibrated Clementine UVVIS and NIR data using a multiple-endmember linear spectral linear unmixing algorithm [13]. The model works either with spectra collected from the image or from laboratory measurements of pure minerals. Components are selected on spectral interpretation and knowledge of lunar soils and surface processes. Variation in the spectral slope varies with surface maturity and TiO2 content [14]. Including a slope endmember in the reference spectral library allows the mineralogy to be mapped independently of maturity effects. [1] Nozette S., et. al., 1994, Science, 266 [2] Lucey P. G., 2004, GRL 31. [3] Pieters C. M. et al., 2006, Icarus, 184. [4] Lucey P. G. et al., 1998, LPSC abstract 1576. [5] Le Mouelic et al., 1999, JGR 104. [6] Eliason E. M. et al., 2003, LPSC abstract 2093. [7] Cahill et al., 2004, LPSC abstract 1469. [8] Gaddis et al., 2007, PDS Volumes USA_NASA_PDS_CL_5001 through 5078. [9] Hapke B., 1981, JGR 86. [10] Johnson P. E., 1983, JGR 88. [11] Li L. and Mustard J. F., 2003, JGR 108. [12] Roberts D. A. et al., 1998, RSE 65. [13] Combe J.-Ph. et al., submitted to PSS. [14] Charette M. P. et al., 1974, JGR 79.
P51B-0495
Laboratory Studies of the Lunar Surface Plasma Sheath and Methods for in situ Plasma Measurements
Surfaces in space exposed to plasmas and UV radiation will become charged and develop a sheath region with an electric field normal to the surface. Typically, this electric field is on the order of a few V/m, too small to lift-off micron sized grains with an expected charge of a single electron on the lunar surface, for example. Much higher electric fields can be generated due to differential UV charging between neighboring lit and dark surface elements, a common situation during sunset or sunrise. The moving lit/dark boundary can also lead to an increased surface charge density, which in combination with the strong localized electric field could lead to the mobilization and transport of the lunar soil. Here we report on a series of ongoing experiments to investigate differential photoelectron charging, and the so- called 'super-charging' effect, related to the moving boundaries between illuminated and dark surfaces. We will also discuss new plasma diagnostic methods to characterize the spatial and energy distribution of electrons in the dilute plasma sheath formed by UV generated emission on the lunar surface.