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Icarus

Volume 274, August 2016, Pages 253-260

https://doi.org/10.1016/j.icarus.2016.02.052 Get rights and content

Abstract

The Mars gravity field resolution is mostly determined by the lower altitude Mars Reconnaissance Orbiter (MRO) tracking data. With nearly four years of additional MRO and Mars Odyssey tracking data since the last JPL released gravity field MRO110C and lander tracking from the MER Opportunity Rover, the gravity field and orientation of Mars have been improved. The new field, MRO120D, extends the maximum spherical harmonic degree slightly to 120, improves the determination of the higher degree coefficients as demonstrated by improved correlation with topography and reduces the uncertainty in the corresponding Mars orientation parameters by up to a factor of two versus previously combined gravity and orientation solutions. The new precession solution is $\dot{ψ} = - 7608.3 \pm 2.1 mas / yr$ and is consistent with previous results but with a reduced uncertainty by 40%. The Love number solution, k₂ = 0.169 ± 0.006, also shows a similar result to previous studies.

Introduction

The initial global high-resolution Mars gravity models were determined using the Mariner 9 and Viking Orbiter S-band Doppler tracking data obtained 1969–1979 (Smith et al., 1993, Konopliv and Sjogren, 1995). However, due to the high elliptical orbits the resolution of the gravity field was not uniform. The first completely uniform global gravity field results occurred with Mars Global Surveyor (MGS) with its nearly circular low altitude (∼380-km periapse) polar frozen orbit and more accurate X-band Doppler tracking data. Initially, multiple independent centers produced high-resolution gravity solutions that were determined from the MGS data (Smith et al., 1999, Lemoine et al., 2001, Yuan et al., 2001; and Konopliv et al., 2006, Marty et al., 2009). The later solution MGS95J includes many years of Mars Odyssey X-band tracking data in a similar orbit as MGS and an improved Mars orientation model that includes Mars nutation.

The Mars Reconnaissance Orbiter (MRO) spacecraft began collecting X-band tracking data on the Mars gravity field in August 2006 (Zuber et al., 2007). The lower altitude (255-km periapse) polar orbit significantly improved the global average resolution of the gravity field from about harmonic degree 70 to harmonic degree 90. The initial JPL MRO based gravity solutions included MRO95A, MRO110B, MRO110B2 as described in Konopliv et al. (2011), and the n = 110 models included MRO tracking data to October 2008. An additional model MRO110C included several more years of MRO data to May 2011. All MRO models are archived with the Planetary Data System (PDS) Geosciences Node (http://geo.pds.nasa.gov/) under the MRO gravity science archive.

A new solution, MRO120D, with MRO tracking data to end of April 2015 is presented in this paper. The additional four years of MRO tracking data has improved the higher degree gravity coefficients. Also the additional 3 years plus of Mars Odyssey data together with newly included four months of Mars Exploration Rover (MER) Opportunity data in the Mars gravity solution improves the Mars orientation solution.

Section snippets

Spacecraft orbiter and lander tracking data

Multiple tracking data sets are included in the development of the Mars gravity field. The Mars orbiter Doppler tracking data are the primary observables for determining the spherical harmonic gravity coefficients, but they also contribute strongly to the Mars orientation solution together with the Mars lander tracking data. The range tracking data are also of primary importance in the determination of the Mars ephemeris and other parameters such as asteroid masses (Konopliv et al., 2011). The

Spacecraft force modeling and estimation technique

The determination of the gravity field and orientation follows the same process of our previous studies (e.g., see Yuan et al., 2001, Konopliv et al., 2006, Konopliv et al., 2011, Konopliv et al., 2013). The orbiter data, as before, are processed in time intervals (or data arcs) of mostly four day lengths where local parameters of spacecraft state, solar pressure factors, atmospheric density corrections, angular momentum desaturation maneuver corrections, and measurement biases are estimated

Gravity and orientation results

Although the new gravity field MRO120D is determined to harmonic degree 120, the actual global resolution is close to degree 95, where the average uncertainty in the coefficients nearly equals the coefficient magnitude. For this reason, the new gravity field is shown in Fig. 3 as the gravity anomaly with the field truncated to degree 95. We estimate the gravity field to a higher degree 120 since some regions (south pole in particular) have higher resolution, and the orbit determination is

Conclusion

Several years of additional MRO and Mars Odyssey orbiter tracking data and MER Opportunity lander data have continued to improve the Mars gravity with higher resolution and more precise orientation parameters including precession, pole location, rotation rate and seasonal spin variations. The next incremental improvement in the Mars gravity field may come from the MAVEN Mars orbiter. MAVEN is in highly elliptic orbit (4.5h period), but it may improve gravity over specific regions where there is

Acknowledgments

The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under Contract with the National Aeronautics and Space Administration.

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An improved JPL Mars gravity field and orientation from Mars orbiter and lander tracking data

Abstract

Introduction

Section snippets

Spacecraft orbiter and lander tracking data

Spacecraft force modeling and estimation technique

Gravity and orientation results

Conclusion

Acknowledgments

Plan. & Sp. Sci.

Icarus

Icarus

Icarus

Icarus

Plan. & Sp. Sci.

Report of the IAU working group on cartographic coordinates and rotational elements: 2009

Celes. Mech. & Dyn. Astron.

Factorization Methods for Discrete Sequential Estimation

Interior structure and seasonal mass redistribution of mars from radio tracking of mars pathfinder

Science

The Planetary and Lunar Ephemeris DE430 and DE431, IPN Progress Report 42-196

Physical Geodesy

Theory of Satellite Geodesy

The JPL Mars Gravity Field, Mars50c, Based Upon Viking and Mariner 9 Doppler Tracking Data

The JPL lunar gravity field to spherical harmonic degree 660 from the GRAIL primary mission

J. Geophy. Res.