P44A-01
Launch of the SELENE(Kaguya) Mission and their Science Goals
Implementation of Lunar orbiting satellite SELENE(Kaguya) has completed after final integration tests of thermal- vacuum and electromagnetic compatibility in the end of February 2007. Through pre-shipping reviews the satellite was carried to JAXA Tanegashima Space Center. The SELENE(Kaguya) is just being launched in September 2007. The mission has started in 1999 FY as a joint project of ISAS and NASDA, which have been merged into a space agency JAXA in October 2003. The SELENE certainly identified as a JAXAfs science mission is operated from the newly installed SOAC (SELENE Operation and data Analysis Center) of Sagamihara/JAXA. The SELENE will be inserted into lunar orbit three weeks after launch using phasing orbit turning around Earth-Moon system. The main satellite will settle into a circular polar orbit with 100km altitude after releasing two sub-satellites in about 40 days after launch. After deploying magnetometer mast and a pair of sounder antenna, initial checks of scientific instruments will be carried for two months. Key questions on lunar science are gWhatfs origin of the Moon?h, gHow does the Moon have evolved?h, and gWhat history does the lunar environment have passed?h Science topics to be studied by using fourteen science instruments are surface composition of chemistry and mineralogy, evolution tectonics of surface including subsurface to 5 km depth, gravity field of whole moon and magnetic field distribution for the study on origin and evolution of the Moon. Lunar environment are investigated in observing charged and neutral particles impinged on the surface. High definition TV cameras are also onboard the SELENE for public outreach. http://www.selene.jaxa.jp
P44A-02
Improvements in Lunar Topographic Knowledge From Laser Altimetry and Tracking
The next few years will see 4 laser altimeters in lunar orbit, for the first time since the Clementine Mission in 1994. Any one of these altimeters will make a significant improvement in our knowledge of the lunar topography but the combined datasets can be expected to revolutionize our understanding of the moon's shape, how it was formed, the processes involved, and its solar illumination. All the missions are nominally in polar orbit ensuring that almost every part of the lunar surface within approximately 10 degrees of the poles, beyond the reach of the Clementine lidar, will be saturated with altimeter measurements. Typically the altimeters will generate 12 orbital profiles per day and will map ~one degree of longitude on each ascending pass. The extensiveness of the coverage will depend not only on the performance of the instruments but also on the duration of each mission, with each ground track improving the coverage density. Gravity fields will benefit from additional coverage and novel tracking systems, which should improve orbital accuracy that will complement the meters-or-less ranging accuracy of these instruments. When tied to the same reference system and selenopotential model, observational and orbital errors and discrepancies between the missions will be identified and corrected to produce a complete topographic model with a horizontal accuracy globally of tens of meters and a radial accuracy of ~one meter. Particularly on the far side, images and other datasets, previously uncertain by many kilometers, may be precisely registered to this model. The vast quantity of data will enable the determination of areas of full and partial shadow at the poles and the hours of illumination at locations of "eternal light". Knowledge of the rotation of the moon over the last many millions of years will permit us to extrapolate into the past the lighting and shadow conditions that are necessary for the formation of near surface deposits of volatile elements.
P44A-03
Gravity Constraints on the Structure of the Marius Hills Volcanic Complex on the Moon
The Marius Hills in central Oceanus Procellarum is the largest volcanic dome complex on the Moon. It is roughly 200 by 250 kilometers across and contains more than 300 volcanic domes and cones and 20 sinuous rilles. Individual domes are up to 25 kilometers across. Volcanic activity in this region is primarily Upper Imbrian in age (3.2-3.8 Ga). On the entire rest of the lunar mare, only about 200 volcanic domes are known, emphasizing the unusual nature of the Marius Hills. Gravity observations provide additional constraints on the structure of the Marius Hills. Individual domes are not resolved in free-air gravity model LP150Q, but the gravity data does resolve the regional structure of the Marius Hills. The overall shape of the gravity anomaly closely corresponds to the outlines of the volcanic field. The maximum anomaly near 14 North, 307 East, is 168 mGal at spherical harmonic degree 65 and 241 mGal at harmonic degree 110. There is a secondary maximum of 113 mGal at 8 North, 309 East, in the southern part of the dome complex. The regional topographic relief is just 500 meters across this region, again at harmonic degree 65. If uncompensated, this topography can only account for at most 40% of the observed free-air gravity anomaly, and even less for reasonable compensation models. Most of the observed gravity anomaly in the Marius Hills must be due to buried, high density material. In this regard, the Marius Hills are similar to some highland volcanos on Mars such as Syrtis Major and Tyrrhena Patera (Kiefer, Earth Planet. Sci. Lett. 222, 349-361, 2004). The density contrast that produces the Marius Hills anomaly is most likely between the surface basalt and the underlying, brecciated anorthositic highland crust. Thus, the gravity observations likely constrain the overall thickness and volume of volcanic activity in the Marius Hills. For plausible density contrasts, the volcanic unit is several kilometers thick. Lunar Prospector Gamma Ray and Neutron Spectrometer observations indicate that basalts in this region have high Ti content, suggesting a high density due to the presence of ilmenite. The densities of high Ti basalts from Apollo samples elsewhere on the Moon are being assessed as possible constraints on the basalt density in the Marius Hills, which will lead to more quantitative constraints on basalt thickness and volume. http://www.lpi.usra.edu/science/kiefer/home.html
P44A-04
Lunar Obliquity History Revisited
In preparation for a LRO (Lunar Reconnaissance Orbiter) related study of possible lunar polar volatiles, we re- examined the lunar orbital and rotational history, with primary focus on the obliquity history of the Moon. Though broad models have been made of lunar obliquity, a cohesive obliquity history was not found. We report on a new model of lunar obliquity including secular changes in inclination of the lunar orbit, tidal dissipation, lunar moments of inertia, and details for periods outside of the stable configurations known as Cassini states. For planets, the obliquity, or angle between the spin and orbit poles, is the dominant control on incident solar radiation. For planetary satellites, the radiation pattern can be more complex, as it depends on the mutual inclinations of three poles; the satellite spin and orbit poles, and the planetary heliocentric orbit pole. Presently, the lunar spin pole and orbit pole co-precess about the ecliptic pole, in a stable situation known as a Cassini state. As a result, permanently shadowed regions near the poles are expected to exist and act as cold traps, retaining water or other volatiles delivered to the surface by comets, solar wind, or via outgassing of the lunar interior. However, tidally driven secular changes in the lunar semimajor axis cause changes in precession rates of the spin and orbit poles, and thereby alter or destabilize the Cassini states. Only one prograde Cassini state exists at present (state 2). In the standard Cassini state model of Ward [1975], two other such states would have existed in the past (states 1 and 4) with the Moon starting in the low obliquity state 1, and remaining there until states 1 and 4 merged and disappear, at roughly half the present Earth-Moon distance. At that point, the Moon transitioned into the currently occupied state 2, and briefly attained very high obliquity values during the transition, and then stayed in state 2 until the present. If correct, this model implies that the transition from state 1 to state 2 is the most important event in the histories of lunar obliquity and polar volatiles, as it separates two periods in which current lunar cold traps could have existed with a period of high polar insolation which could have mobilized volatiles into space or to greater depths in the lunar near surface. If incorrect, lunar cold traps may prove only a very recent phenomenon. By including secular orbit changes, our model should help determine if this Cassini state stability really dominated in the past and allow detailed examination of extra-Cassini state periods.
P44A-05
Isolated Lunar Magnetic Anomalies: Relation to Surface Albedo and Interaction with the Solar Wind
In this paper, we investigate more quantitatively the potential role of lunar crustal magnetization in producing swirl-like high-albedo markings on the lunar surface. For this purpose, we make use of a recently produced global map of the vector lunar magnetic field. Improving upon previously available data, the new map provides extended coverage of the strong Descartes Mountains anomaly and data for areas that had not previously been mapped. This global map was produced using LP-MAG data from quiet external conditions (when the Moon was in the solar wind and the spacecraft in the lunar wake, and data from the geomagnetic tail). However, passes were also identified where external field contamination was relatively low from times when the Moon was in the solar wind and the spacecraft was on the dayside. These data measure the combined crustal and solar wind magnetic fields. In combination with measurements from quiet external conditions, these data can be used to investigate the way in which the crustal anomalies interact with the solar wind and identify possible lunar mini- magnetospheres. Here, we present (1) forward modeling results of anomaly source properties, including source geometry and directions of magnetization, for isolated anomalies near craters Abel and Airy (using LP-MAG data from quiet external conditions), and (2) a comparison of LP-MAG measurements for the isolated anomalies obtained under different external conditions. These anomalies have been selected because they are both relatively strong, but while a high albedo marking has been mapped at Airy, it is not certain that there is an albedo anomaly at Abel. The model results will be used to discuss more quantitatively whether the sources of isolated anomalies are collocated with regions of unusual albedo, and whether the direction of magnetization affects the apparent association between the crustal anomalies and lunar albedo. The results comparing coverage of the Abel and Airy anomalies under different external conditions will be used to discuss the possible existence of mini-magnetospheres at those locations, further investigating the potential role of magnetization in producing high albedo swirls on the Moon.
P44A-06
The Uppermost Surface of the Moon: A Study of the Ap16 Clam Shell Samples
The Apollo 16 Clam Shell Sampling Devices (CSSDs) sampled the uppermost surface of the lunar soil. The two devices used beta cloth (69003) and velvet (69004) to collect soil from the uppermost 100 μm and 500 μm of the soil, respectively. Although very little material was collected, recent advances in instrumentation and sample preparation techniques allow for detailed analysis of these precious samples thirty years after their collection. Understanding the properties of the uppermost surface is critical as it is the optical surface that is probed by remote-sensing data, like that which will be generated by instruments on upcoming missions (e.g. M3). The uppermost material is also the surface with which future lunar astronauts and their equipment will be in direct contact, and thus understanding its properties will be important for dust mitigation and toxicology issues, as well as resource utilization (ISRU) purposes. In combination with traditional skim (69921) and scoop (69941) samples (sampling to depths of roughly 0.5 cm and 3 cm, respectively) that were taken at the same location, these CSSD samples provide a near surface soil profile that is allowing us to investigate the properties of the uppermost surface. The recent success of the Lunar Soil Characterization Consortium (LSCC) has shown the utility of combining several techniques to fully characterize a soil through integrated study; we use the same approach here. This holistic perspective allows us to make crucial connections between the physical, optical, and chemical properties of the soil. First results of the Vis/NIR spectra suggest that while the deeper samples (69921, 69941) are indistinguishable from one another, the velvet sample (69004) is both darker and redder by comparison, indicating a greater accumulation of weathering products at the surface. Magnetic measurements and preliminary mineralogical analyses are in progress.
P44A-07
Viscous topographic relaxation on Mercury revisited: Improved constraints on Mercury's crustal thickness
The crustal thickness of Mercury is only poorly constrained. Current estimates based on the observed center of mass - center of figure offset yield large crustal thickness values of 100-300 km. Further constraints on Mercury's crustal thickness may be obtained from the degree of topographic relaxation observed on the surface. Isostatically compensated loads induce lateral pressure gradients which can drive flow in the lower crust if the temperatures there are sufficiently high. The efficiency of the crustal flow and the degree of topographic relaxation depend on the temperature structure of the crust and therefore the crustal thickness, which may thus be constrained from the presence or absence of long wavelength topography. Impact structures on Mercury like the Caloris basin have been shown to be in a state close to total isostatic compensation for diameters larger than ~ 800 km. Since these structures do not show evidence for large scale topographic relaxation, crustal flow on Mercury cannot have been significant since the time of their emplacement in the pre-Tolstojan era around 4 Gyr. This stability of long-wavelength topography has been used by Nimmo (2002) to constrain Mercury's crustal thickness. Depending on crustal rheology and the distribution of heat sources in the interior, he could tighten the bounds on Dc to 100-200 km. We have reanalyzed the conditions under which the temperatures in Mercury's lower crust are sufficient to induce large scale flow, thus relaxing isostatically supported topography. Contrary to the previous study by Nimmo (2002), we use parametrized thermal evolution models to calculate the crust's thermal structure, taking secular cooling and a poorly conducting regolith layer into account. The results show that the survival of long-wavelength topography over the last 4 Gyr implies a crustal thickness of less than 100 km. Furthermore, if the thickness of the regolith layer approaches that of the lunar regolith, the average crustal thickness cannot be larger than 85 km. Nimmo, F., 2002. Constraining the crustal thickness on Mercury from viscous topographic relaxation, Geophys. Res. Lett., 29, doi:10.1029/2001GL013883.
P44A-08
Color Studies of the Surface of Mercury: A Pre-MESSENGER View
Mariner 10 visited the planet Mercury during three flybys in 1974-75. Images obtained by its twin vidicon cameras through orange (575 nm) and UV (355 nm) filters during the first and second flyby have been radiometrically calibrated, photometrically normalized, and reprojected to a common map format. This effort has produced color mosaics (UV and orange) for the first-encounter incoming (3-km/pixel) and outgoing (4-km/pixel) portions of the planet. These datasets provide important information on mercurian color characteristics, and offer a preview of the data that will be returned by the MESSENGER spacecraft during its first Mercury flyby in January, 2008. The color data for Mercury is interpreted within the framework of understanding developed through remote sensing and returned-sample studies of the Moon. The co-registered UV and orange mosaics allow spectral parameter maps to be constructed. If the lunar assumptions hold for Mercury, then one parameter is a measure of the combined effects of ferrous iron abundance and maturity and the other is related to the abundance of opaque phases. "Maturity" is a term used to describe the extent to which materials have been modified by the solar wind (implantation and sputtering) and bombardment by micrometeorites and cosmic rays. The spectral parameter images reveal embayment relationships at the edges of some plains units suggestive of emplacement by effusive volcanism. Elsewhere, the color and morphology of some dark deposits are consistent with pyroclastic activity. Other low-albedo materials show no color difference relative to the global average. Examination of impact craters in the opaque-phase map demonstrates that at some locations material excavated from depth has a lower abundance of opaques than the average surface. This stratigraphy may be the result of magma ocean processes similar to those on the Moon. Crater rays are bright predominantly because they are composed of fresh, unweathered (immature) material, though inherent compositional and albedo contrasts with the substrate contribute to the brightness of some rays. We will provide additional results from our on-going analysis of the two-color data for the outgoing hemisphere. This area is home to craters with dark haloes, extremely long arcuate crater rays, and plains materials associated with the Caloris basin. We will also recap observational plans for the MESSENGER encounter in January, 2008.