Gravity Recovery And Interior Laboratory Mission Research Articles

Scaliger Crater Region on the Moon: Implications for the Australe North Basin and magmatism in the region

Australe North (35.5°S, 96°E) is a pre-Nectarian impact basin north of Mare Australe, first identified using the GRAIL data. It does not show clear topographic signatures typical of any large impact structure on the Moon. However, results from GRAIL (Gravity Recovery and Interior Laboratory) mission suggested the presence of a ∼ 880 km wide basin whose boundary does not coincide with the earlier identified Australe Basin. In this study, we investigate the Scaliger Crater region to understand the controls that the proposed Australe North Basin played on the local geology in the region. The location of the Scaliger Crater at the intersection of the rims of two pre-Nectarian Basins, Milne and the proposed Australe North provides a unique geological setting to reconstruct the region's geological history. We provide geological evidence substantiating the existence of the rim of the Australe North Basin, as has been proposed using gravity data. Based upon the spectral signatures and morphometry, we suggest the presence of a mafic pluton and/or lower crustal/mantle rocks in the region and provide constraints on its emplacement timescale. For the first time, Late-stage volcanism has been reported inside the Bowditch Crater and Lacus Solitudinis, emplaced at ∼1.7 Ga and ∼ 2.3 Ga, respectively, suggesting prolonged volcanism at the eastern lunar nearside-farside boundary inside an obscured pre-Nectarian basin.

Lunar ephemeris at sub microarcsecond accuracy (LESMA) leads to sub-millimeter positional accuracy of the moon

The most accurate LLR (lunar laser ranging) initiative, named APOLLO (apache point observatory lunar laser-ranging operation) demonstrated millimeter-range positional accuracy in 2009, thus improving LLR by one order-of-magnitude. Since, LLR is a foundational technique in studying gravity, Murphy (principal investigator of APOLLO) stated in 2009, that with this millimeter-range accuracy, the simulation model has been found to be the limiting-factor in extracting the theoretical science results, and hence, we should: (1) develop the science case and expand our ability to model LLR for a new regime of high precision, (2) develop the theoretical tools for honing the science case for submillimeter LLR, and (3) explore which model/code is worth putting our efforts into. (4) Since millimeter-quality data are a recent development, the model effort lags. (5) Finally, we will code-in new physics so that we may simulate sensitivities. In connection with simulation model/code, Murphy stated in 2013, that among the four available LLR simulation models: JPL (jet propulsion laboratory), CfA (the Harvard-Smithsonian center for astrophysics), LU (leibniz University, Hannover, Germany), and IMCCE (Institut de Mecanique celeste et de calcul des Ephemerides, France), the JPL model currently produces weighted RMS (root-mean-square) residuals at ∼18 mm, which is about half of the other models; so, clearly a gap exists from millimeter ranging-precision of APOLLO. Hence, the CfA, LU, and IMCCE are engaged, since 2013, in a stepwise comparative streamlining effort to identify the model-differences, errors, and shortcomings. All the four available LLR simulation models can be classified as GR (general relativity)-astronomers model; they are basically similar. Professor Douglas Currie of the University of Maryland, College Park, NASA Lunar Science Institute, stated in a Conference presentation, in 2012, that Ground stations, that is, the lunar observatories, have improved by a factor of 200, but the agreement between observations and fitted theory has plateaued at ∼2 cm over the past two decades. However, no substantial progress on improving the fit has been reported in the published literature, till date. Based on about a quarter-century of experience in doing high-precision numerical simulation of celestial orbits, the authors have developed LESMA (lunar Ephemeris at sub Microarcsecond accuracy) utilizing the methodology of evolved general relativity (EGR) that has incorporated the following two concepts: (1) Relativistic time for integration and (2) methodology of conservation of magnitude of the angular momentum, MΦ , for Φ-rotation (in addition to the θ-rotation that leads to the rosetting ellipse) of the orbital plane. Incorporation of the two above-mentioned concepts has led to three orders-of-magnitude accuracy-improvement of the computed (1) precession (compared to JPL's DE405) of Lunar orbit, as verified using three independent methods and (2) radial position (compared to JPL's DE430/431) of the Moon. LESMA will enable scientists to make efficient use of research-funds from NASA, etc., for production of new science results from APOLLO. LESMA will also be useful for getting better science results (than Folkner reported {in 2014} submeter accurate Position of the Moon) from the GRAIL (gravity recovery and Interior laboratory) mission (costing 500 million USD), by spending a little more for revisiting the computations, utilizing LESMA data.

Comparison and analysis on lunar rotation with lunar gravity field models

Understanding the structure of and dynamic processes in the deep interior of planets is crucial for understanding their origin and evolution. An effective way to constrain them is through observation of rotation and subsequent simulation. In this paper, a numerical model of the Moon’s rotation and orbital motion is developed based on previous studies and implemented independently. The Moon is modeled as an anelastic body with a liquid core. The equations of the rotation were nonlinear and the Euler angles are cross coupled. We solve them numerically via the Runge-Kutta-Fehlberg (RKF) and multi-steps Adams-Bashforth-Moulton (ABM) predictor-corrector numerical integration. We have found that adequate accuracy is maintained by taking twelve steps per day using eleventh differences in the integrating polynomial. The lunar orbital and rotational equations are strongly coupled, so we integrated the rotation and motion simultaneously. We refer to other planetary informations from the newest planetary and lunar ephemeris INPOP17a, which is reported had fitted the longest LLR (Lunar Laser Ranging) observation data. Using the model GL660B from GRAIL (Gravity Recovery and Interior Laboratory) mission, we firstly compare our numerical results with the INPOP17a to prove the reasonability of our model. After that we apply the lunar gravity model CEGM02 determined from Chang’E-1 mission and SGM100h from SELENE mission to our model, the difference between results from CEGM02 and GL660B are less than $-0.20 \sim0.15$ arc-second, and $-0.25 \sim0.20$ arc-second for GL660B and SGM100h. Compared to SGM100h, the results show that the low degree and order coefficients (less than 6 from this paper) of lunar gravity field were improved in CEGM02 as expected. It is the first time to demonstrate that these models can be applied to lunar rotation model. These results manifest that a development of the gravity field measure will help us to know the rotation motion more precisely.

Lunar interior properties from the GRAIL mission

The Gravity Recovery and Interior Laboratory (GRAIL) mission has sampled lunar gravity with unprecedented accuracy and resolution. The lunar GM, the product of the gravitational constant G and the mass M, is very well determined. However, uncertainties in the mass and mean density, 3345.56 ± 0.40 kg/m3, are limited by the accuracy of G. Values of the spherical harmonic degree-2 gravity coefficients J2 and C22, as well as the Love number k2 describing lunar degree-2 elastic response to tidal forces, come from two independent analyses of the 3 month GRAIL Primary Mission data at the Jet Propulsion Laboratory and the Goddard Space Flight Center. The two k2 determinations, with uncertainties of ~1%, differ by 1%; the average value is 0.02416 ± 0.00022 at a 1 month period with reference radius R = 1738 km. Lunar laser ranging (LLR) data analysis determines (C − A)/B and (B − A)/C, where A < B < C are the principal moments of inertia; the flattening of the fluid outer core; the dissipation at its solid boundaries; and the monthly tidal dissipation Q = 37.5 ± 4. The moment of inertia computation combines the GRAIL-determined J2 and C22 with LLR-derived (C − A)/B and (B − A)/C. The normalized mean moment of inertia of the solid Moon is Is/MR2 = 0.392728 ± 0.000012. Matching the density, moment, and Love number, calculated models have a fluid outer core with radius of 200–380 km, a solid inner core with radius of 0–280 km and mass fraction of 0–1%, and a deep mantle zone of low seismic shear velocity. The mass fraction of the combined inner and outer core is ≤1.5%.

Determination and localized analysis of intersatellite line of sight gravity difference: Results from the GRAIL primary mission

AbstractThe line of sight (LOS) gravity difference between two coorbiting spacecrafts is determined in terms of intersatellite range‐acceleration measurements available from the Gravity Recovery and Interior Laboratory (GRAIL). The precise orbit data are crucial for retrieving gravity difference from range acceleration and aligning the LOS data particularly in altitude. A relative orbit error of a few centimeters in position and a few tens µm/s in velocity is commensurate with the GRAIL‐ranging instrument noise at a few μGal in LOS gravity difference. The power spectrum, as well as the topography correlation and admittance, is quantified by upward continuing the topographic potential, forward modeling the LOS gravity along the spacecraft trajectory (i.e., Bouguer correction) and comparing with the GRAIL LOS observations. Based on the data analysis from the primary GRAIL mission, I found that the LOS gravity difference observation produced near unity correlation with topography potential out to degree 550, higher than the global estimate, over the areas covered by the low‐altitude orbit (~20 km). The crustal density was estimated to be 2500–2600 kg/m3 with regional variations of about 10%, by minimizing the Bouguer coherence of the GRAIL data at the degree band 150–300. Systematic decrease in the density estimates by 3–4% or 100 kg/m3 was observed at shorter wavelengths (degree band 300–500). It implies the inadequacy of a uniform density model across the entire lithosphere and suggests radial stratification of the bulk density (or porosity). Due to spatially localized characteristic, the LOS gravity difference data are well suited to regional analysis at the highest‐possible resolution.

General relativistic observables of the GRAIL mission

We present a realization of astronomical relativistic reference frames in the Solar System and its application to the Gravity Recovery and Interior Laboratory (GRAIL) mission. We model the necessary space-time coordinate transformations for light-trip time computations and address some practical aspects of the implementation of the resulting model. We develop all the relevant relativistic coordinate transformations that are needed to describe the motion of the GRAIL spacecraft and to compute all observable quantities. We take into account major relativistic effects contributing to the dual one-way range observable, which is derived from one-way signal travel times between the two GRAIL spacecrafts. We develop a general relativistic model for this fundamental observable of GRAIL, accurate to $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. We develop and present a relativistic model for another key observable of this experiment, the dual one-way range rate, accurate to $1\text{ }\text{ }\ensuremath{\mu}\mathrm{m}/\mathrm{s}$. The presented formulation justifies the basic assumptions behind the design of the GRAIL mission. It may also be used to further improve the already impressive results of this lunar gravity recovery experiment after the mission is complete. Finally, we present transformation rules for frequencies and gravitational potentials and their application to GRAIL.

New map of lunar gravity gives insight into Moon's early history

A new map of the Moon's gravity field, created by NASA's Gravity Recovery and Interior Laboratory (GRAIL) mission, provides a detailed view of the Moon's many impact craters, evidence for ancient volcanic structures, and new estimates of the thickness of the lunar crust. Scientists announced the results from the first phase of the GRAIL mission at the AGU Fall Meeting; the results are also reported in three papers in the journal Science. GRAIL, launched in September 2011, consists of two satellites that send signals to each other. When a region of stronger gravity pulls on one satellite more than the other, the distance between the two changes. By measuring changes in the distance between the two satellites, researchers can create a map of the Moon's gravity field. The same method is used by the twin satellites of NASA's Gravity Recovery and Climate Experiment mission to measure Earth's gravity field.

Lunar floor‐fractured craters: Classification, distribution, origin and implications for magmatism and shallow crustal structure

Floor‐Fractured Craters (FFCs) are a class of lunar craters characterized by anomalously shallow floors cut by radial, concentric, and/or polygonal fractures; additional interior features are moats, ridges, and patches of mare material. Two formation mechanisms have been hypothesized—floor uplift in response to shallow magmatic intrusion and sill formation, and floor shallowing in response to thermally driven viscous relaxation. This study combines new Lunar Orbiter Laser Altimeter (LOLA) and Lunar Reconnaissance Orbiter Camera (LROC) data to characterize and categorize the population of FFCs and map their distribution on the Moon, and uses variations in floor‐fractured crater morphology and regional distribution to investigate the proposed formation mechanisms. The population of FFCs was categorized according to the classes outlined by Schultz (1976). The distribution of these FFC categories shows an evolution of crater morphology from areas adjacent to lunar impact basins to areas in the lunar highlands. We propose that this trend is supportive of formation by shallow magmatic intrusion and sill formation—crustal thickness determines the magnitude of magmatic driving pressure, and thus either piston‐like floor uplift for high magnitude, or a convex floor profile for low magnitude. Predictions from previous studies modeling viscous relaxation are inconsistent with the observed altimetric profiles of FFCs. Hence our analysis favors FFC formation by shallow magmatic intrusion, with the variety of FFC morphologies being intimately linked with location and crustal thickness, and the driving pressure of the intrusion. Data from the GRAIL (Gravity Recovery and Interior Laboratory) mission will help to test these conclusions.