Evidence of large empty lava tubes on the Moon using GRAIL gravity (original) (raw)

GRAIL gravity constraints on the vertical and lateral density structure of the lunar crust

(2014), GRAIL gravity constraints on the vertical and lateral density structure of the lunar crust, Abstract We analyzed data from the Gravity Recovery and Interior Laboratory (GRAIL) mission using a localized admittance approach to map out spatial variations in the vertical density structure of the lunar crust. Mare regions are characterized by a distinct decrease in density with depth, while the farside is characterized by an increase in density with depth at an average gradient of ∼35 kg m −3 km −1 and typical surface porosities of at least 20%. The Apollo 12 and 14 landing site region has a similar density structure to the farside, permitting a comparison with seismic velocity profiles. The interior of the South Pole-Aitken (SPA) impact basin appears distinct with a near-surface low-density (porous) layer 2–3 times thinner than the rest of the farside. This result suggests that redistribution of material during the large SPA impact likely played a major role in sculpting the lunar crust.

Gravity Field of the Moon from the Gravity Recovery and Interior Laboratory (GRAIL) Mission

Science, 2012

The Holy GRAIL?The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission.Zuberet al.(p.668, published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively.Wieczoreket al.(p.671, published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally,Andrews-Hannaet al.(p.675, published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history.

Earhart: A Large, Previously Unknown Lunar Nearside Crater Revealed by Grail Gradiometry

Introduction: As a part of NASA's Discovery Program, the Gravity Recovery and Interior Laboratory (GRAIL) vehicles were launched in September 2011. The sister spacecraft, Ebb and Flow, mapped lunar gravity to an unprecedented precision [1]. High resolution data is currently being utilized to gain a greater understanding of the Moon's interior. Through gravita-tional analysis of the Moon, subsurface features are also detected. In the current investigation, gravity mapping data collected at different altitudes is applied to detect, characterize, and validate the presence of buried craters. The free-air gravity coupled with Bouguer gravity (corrected for topography and terrain) aids in recognizing gravitational footprints that may correspond to subsurface density anomalies. Detection of buried features is further supported by individually analyzing free-air and Bouguer gravity maps. Furthermore , forward modeling supports the detection and validates the existence of buried crat...

Gravity Recovery and Interior Laboratory (GRAIL): Mapping the Lunar Interior from Crust to Core

Space Science Reviews, 2013

The Gravity Recovery and Interior Laboratory (GRAIL) is a spacecraft-to-spacecraft tracking mission that was developed to map the structure of the lunar interior by producing a detailed map of the gravity field. The resulting model of the interior will be used to address outstanding questions regarding the Moon's thermal evolution, and will be applicable more generally to the evolution of all terrestrial planets. Each GRAIL orbiter contains a Lunar Gravity Ranging System instrument that conducts dual-one-way ranging measurements to measure precisely the relative motion between them, which in turn are used to develop the lunar gravity field map. Each orbiter also carries an Education/Public Outreach payload, Moon Knowledge Acquired by Middle-School Students (MoonKAM), in which middle school students target images of the Moon for subsequent classroom analysis. Subsequent to a successful launch on September 10, 2011, the twin GRAIL orbiters embarked on independent trajectories on a 3.5month-long cruise to the Moon via the EL-1 Lagrange point. The spacecraft were inserted into polar orbits on December 31, 2011 and January 1, 2012. After a succession of 19 maneuvers the two orbiters settled into precision formation to begin science operations in March 1, 2012 with an average altitude of 55 km. The Primary Mission, which consisted of three 27.3-day mapping cycles, was successfully completed in June 2012. The extended mission will permit a second three-month mapping phase at an average altitude of 23 km. This paper provides an overview of the mission: science objectives and measurements, spacecraft and instruments, mission development and design, and data flow and data products.

Detection and characterization of buried lunar craters with GRAIL data

We used gravity mapping observations from NASA's Gravity Recovery and Interior Laboratory (GRAIL) to detect, characterize and validate the presence of large impact craters buried beneath the lunar maria. In this paper we focus on two prominent anomalies detected in the GRAIL data using the gravity gradiom-etry technique. Our detection strategy is applied to both free-air and Bouguer gravity field observations to identify gravitational signatures that are similar to those observed over buried craters. The presence of buried craters is further supported by individual analysis of regional free-air gravity anomalies, Bouguer gravity anomaly maps, and forward modeling. Our best candidate, for which we propose the informal name of Earhart Crater, is approximately 200 km in diameter and forms part of the northwestern rim of Lacus Somniorum, The other candidate, for which we propose the informal name of Ashoka Anomaly, is approximately 160 km in diameter and lies completely buried beneath Mare Tranquillitatis. Other large, still unrecognized, craters undoubtedly underlie other portions of the Moon's vast mare lavas.

Lunar interior properties from the GRAIL mission

Journal of Geophysical Research: Planets, 2014

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/m 3 , are limited by the accuracy of G. Values of the spherical harmonic degree-2 gravity coefficients J 2 and C 22 , as well as the Love number k 2 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 k 2 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 À A)/B and (B À 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 J 2 and C 22 with LLR-derived (C À A)/B and (B À A)/C. The normalized mean moment of inertia of the solid Moon is I s /MR 2 = 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%.

Strategies for Detection of Buried Empty Lava Tubes with GRAIL Data

AIAA SPACE 2014 Conference and Exposition, 2014

The success of the NASA's GRAIL mission -a twin spacecraft formation revolving around the Moon in a quasi-circular polar orbit -currently provides the highest resolution and most accurate gravity data for the Moon. The low altitude at which some of these data were collected in the GRAIL extended mission potentially allows the detection of small-scale surface or subsurface features. This analysis is focused on the detection of the presence and extent of empty lava tubes beneath the mare surface.

Analyzing GRAIL data: first lunar gravity field solutions at AIUB

The NASA mission GRAIL (Gravity Recovery and Interior Laboratory, Zuber et al, 2013) inherited its concept from the GRACE (Gravity Recovery and Climate Experiment) mission to determine the gravity field of the Moon. The presence of Ka-band range measurements (Asmar et al, 2013) enables data acquisition even when the spacecraft are not Doppler-tracked from the Earth, thus allowing for the first time the accurate determination of the gravity field on both the near and far side of the Moon. Such knowledge is essential to improve the understanding of the Moon's internal structure and thermal evolution (Wieczorek et al, 2013). Currently, two official GRAIL gravity field models resolve the selenopotential up to degree and order 900: GL0900D (Konopliv et al, 2014) and GRGM900C (Lemoine et al, 2014). These solutions were obtained using the software packages MIRAGE, a gravity processing version of the JPL Orbit Determination Program, and GEODYN, respectively. The first AIUB lunar gravity...