An improved gravity model for Mars: Goddard Mars model 1

Abstract

Doppler tracking data of three orbiting spacecraft have been reanalyzed to develop a new gravitational field model for the planet Mars, Goddard Mars Model 1 (GMM‐1). This model employs nearly all available data, consisting of approximately 1100 days of S band tracking data collected by NASA's Deep Space Network from the Mariner 9 and Viking 1 and Viking 2 spacecraft, in seven different orbits, between 1971 and 1979. GMM‐1 is complete to spherical harmonic degree and order 50, which corresponds to a half‐wavelength spatial resolution of 200–300 km where the data permit. GMM‐1 represents satellite orbits with considerably better accuracy than previous Mars gravity models and shows greater resolution of identifiable geological structures. The notable improvement in GMM‐1 over previous models is a consequence of several factors: improved computational capabilities, the use of optimum weighting and least squares collocation solution techniques which stabilized the behavior of the solution at high degree and order, and the use of longer satellite arcs than employed in previous solutions that were made possible by improved force and measurement models. The inclusion of X band tracking data from the 379‐km altitude, near‐polar orbiting Mars Observer spacecraft should provide a significant improvement over GMM‐1, particularly at high latitudes where current data poorly resolve the gravitational signature of the planet.

Construction of Martian Interior Model

“…The equilibrium value lies within −(7.62-7.92) × 10 -6 , that is, is about equal to half of the observed value J 4 = -15.4476 × 10 -6 (Smith et al, 1993).…”

Deep-seated thrust faults bound the Mare Crisium lunar mascon

“…Because of the occurrence of sets of arcuate wrinkle ridges in other maria associated with free-air gravity anomalies, our results are likely applicable to other lunar mascon basins. Moreover, as mascons have also been reported on Mars (Smith et al, 1993) and Mercury (Smith et al, 2012), these findings may give fresh insight into the formation and evolution of mascons on terrestrial worlds in general.…”

“…Conversely, deep-seated thrust faults might not form without a collar of thickened crust, and where the central positive gravity anomaly is from volcanic loading alone, as is likely the case for the mascons associated with the Argyre and Isidis basins on Mars (Smith et al, 1993). Neither Argyre nor Isidis possess an annular topographic bench, and so it may be that those basins do not host mascon-bounding, deeply rooted thrust faults.…”

An improved solution of the gravity field of Mars (GMM‐2B) from Mars Global Surveyor

“…For GMM-2B these data are independent, since the historical data were not included in the gravity solution. The RMS of fit for Viking and Mariner 9 is compared in Table 8 with results obtained from the models GMM-1 [Smith et al, 1993] and Mars50c [Konopliv and Sjogren, 1995], which were models determined solely from the historical data. The RMS is computed separately for each distinct spacecraft orbit type for both the Doppler and the range data so we can compare the performance for different orbit geometries.…”