The gravity field of Mars: results from Mars Global Surveyor.

Observations of the gravity field of Mars reveal a planet that has responded differently in its northern and southern hemispheres to major impacts and volcanic processes. The rough, elevated southern hemisphere has a relatively featureless gravitational signature indicating a state of near-isostatic compensation, whereas the smooth, low northern plains display a wider range of gravitational anomalies that indicates a thinner but stronger surface layer than in the south. The northern hemisphere shows evidence for buried impact basins, although none large enough to explain the hemispheric elevation difference.

Europa's differentiated internal structure: inferences from four Galileo encounters.

Radio Doppler data from four encounters of the Galileo spacecraft with the jovian moon Europa have been used to refine models of Europa's interior. Europa is most likely differentiated into a metallic core surrounded by a rock mantle and a water ice-liquid outer shell, but the data cannot eliminate the possibility of a uniform mixture of dense silicate and metal beneath the water ice-liquid shell. The size of a metallic core is uncertain because of its unknown composition, but it could be as large as about 50 percent of Europa's radius.

Improved gravity field of the moon from lunar prospector.

An improved gravity model from Doppler tracking of the Lunar Prospector (LP) spacecraft reveals three new large mass concentrations (mascons) on the nearside of the moon beneath the impact basins Mare Humboltianum, Mendel-Ryberg, and Schiller-Zucchius, where the latter basin has no visible mare fill. Although there is no direct measurement of the lunar farside gravity, LP partially resolves four mascons in the large farside basins of Hertzsprung, Coulomb-Sarton, Freundlich-Sharonov, and Mare Moscoviense. The center of each of these basins contains a gravity maximum relative to the surrounding basin.

Distribution of rock, metals, and ices in Callisto.

Radio Doppler data from a single encounter (C3) of the Galileo spacecraft with Callisto, the outermost Galilean moon of Jupiter, indicated that Callisto was probably undifferentiated. Now, similar data from a second encounter (C9) corroborate this conclusion, but more accurate data from a third encounter (C10) indicate that the rock and ice within Callisto have partially, but not completely, separated. Callisto may be differentiated into a rock-metal core less than 25 percent of Callisto's radius, an outer layer of clean ice less than 350 km thick, and a middle layer of mixed rock and ice.

Europa's differentiated internal structure: inferences from two Galileo encounters.

Doppler data generated with the Galileo spacecraft's radio carrier wave during two Europa encounters on 19 December 1996 (E4) and 20 February 1997 (E6) were used to measure Europa's external gravitational field. The measurements indicate that Europa has a predominantly water ice-liquid outer shell about 100 to 200 kilometers thick and a deep interior with a density in excess of about 4000 kilograms per cubic meter. The deep interior could be a mixture of metal and rock or it could consist of a metal core with a radius about 40 percent of Europa's radius surrounded by a rock mantle with a density of 3000 to 3500 kilograms per cubic meter.

Gravitational evidence for an undifferentiated Callisto.

Before the arrival of the Galileo spacecraft at Jupiter, models for the interior structure of the four galilean satellites--Io, Europa, Ganymede and Callisto-ranged from uniform mixtures of rock and ice (that is, undifferentiated objects) or rocky cores surrounded by a mantle of water ice. Now it appears that Io has a large metallic core and that Ganymede is strongly differentiated, most probably into a three-layer structure consisting of a metallic core, a silicate mantle and a deep outer layer of ice. Direct information on the interior structure of Callisto determined from previous spacecraft fly-bys was essentially limited to an estimate of the mean density being intermediate between pure ice and pure rock.

Galileo Gravity Results and the Internal Structure of Io.

Doppler data generated with the Galileo spacecraft's radio carrier wave were used to measure Io's external gravitational field. The resulting triaxial field is consistent with the assumption that Io is in tidal and rotational equilibrium. The inescapable conclusion is that it has a large metallic core.

Gravity field of venus: a preliminary analysis.

The line-of-sight gravity field for Venus has been mapped by tracking the Pioneer Venus spacecraft in the vicinity of periapsis for a 45 degrees swath of longitude eastward of 294 degrees . There are consistent and systematic variations in the gravity signature from orbit to orbit, attesting to the reality of observed anomalies. Orbit 93 passes over a large positive topographic feature, the "northern plateau," for which there is no corresponding gravity signature.

Mars gravity: high-resolution results from viking orbiter 2.

Doppler radio-tracking data have provided detailed measurements for a martian gravity map extending from 30 degrees S to 65 degrees N in latitude and through 360 degrees of longitude. The feature resolution is approximately 500 kilometers, revealing a huge anomaly associated with Olympus Mons, a mascon in Isidis Planitia, and other anomalies correlated with volcanic structure. Olympus Mons has been modeled with a 600-kilometer surface disk having a mass of 8.

Lunar Shape via the Apollo Laser Altimeter.

Data from the Apollo 15 and Apollo 16 laser altimeters reveal the first accurate elevation differences between distant features on both sides of the moon. The large far-side depression observed in the Apollo 15 data is not present in the Apollo 16 data. When the laser results are compared with elevations on maps from the Aeronautical Chart and Information Center, differences of 2 kilometers over a few hundred kilometers are detected in the Mare Nubium and Mare Tranquillitatis regions.

Mariner 9 celestial mechanics experiment: gravity field and pole direction of Mars.

Analysis of the Mariner 9 radio-tracking data shows that the Martian gravity field is rougher than that of Earth or the moon, and that the accepted direction of Mars's rotation axis is in error by about 0.5 degrees . The new value for the pole direction for the epoch 1971.

Lunar Gravity via Apollo 14 Doppler Radio Tracking.

Gravity measurements at high resolution were obtained over a 100-kilometer band from + 70 degrees to -70 degrees of longitude during the orbits of low periapsis altitude (approximately 16 kilometers). The line-of-sight accelerations are plotted on Aeronautical Chart and Information Center mercator charts (scale 1 : 1,000,000) as contours at 10-milligal intervals. Direct correlations between gravity variations and surface features are easily determined.

Lunar Gravity over Large Craters from Apollo 12 Tracking Data.

The Doppler residuals from the Apollo 12 lunar module radio tracking data indicate large negative accelerations over the craters Ptolemaeus and Albategnius. The mass deficienicies required to produce these accelerations are approximately equivalent to the removal of the surface material to a depth of 1 kilometer over the entire area of these craters. Several other features of the gravity fine structure can also be correlated with topography.

Nonexistence of large mascons at mare marginis and mare orientale.

The analysis of line-of-sight residual accelerations from Lunar Orbiters 3 and 5 does not show any evidence for large mascons near the lunar limbs. Although unfavorable geometry reduces the acceleration effect due to any mascon near the limb, simulations show that large masses at Mare Orientale and Mare Marginis would produce substantial accelerations, in complete disagreement with the actual Doppler tracking data obtained from a Lunar Orbiter experiment.

Mascons: lunar mass concentrations.

Lunar Orbiter tracking data have been processed to supply a qualitatively consistent gravimetric map of the lunar nearside. While a simplified model was employed, the results indicate that there are large mass concentrations under the lunar ringed maria. These mass concentrations may have important implications for the various theories regarding lunar history.

Gravitational inconsistency in the lunar theory: confirmation by radio tracking.

When range and Doppler observations of space probes near or on Moon are reduced by use of a lunar ephemeris calculated from the Brown lunar theory, residuals as large as 440 meters in position and 1.5 millimeters per second in velocity are observed. When the calculations are repeated with use of LE 5, the integrated lunar ephemeris described (1), the residuals are greatly reduced.

Lunar gravity: preliminary estimates from lunar orbiter.

Tracking data fromt the lunar orbiters have been analyzed for information regarding Moon's gravity field. These preliminary results include values of a set of harmonic coefficients throlugh degree 4 in the tesserals and degree 8 in the zonals. Implications regarding Moon's mass distribution are discltssed: one implicationt is that Moon is nearly homogeneous.

Lunar orbiter ranging data: initial results.

Data from two Lunar Orbiter spacecraft have been used to test the significance of corrections to the lunar ephemeris. Range residuals of up to 1700 meters were reduced by an order of magnitude by application of the corrections, with most of the residuals reduced to less than 100 meters. Removal of gross errors in the ephemeris reveals residual patterns that may indicate errors in location of observing stations, as well as the expected effects of Lunar nonsphericity.