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The equatorial shape and gravity field of Mercury from MESSENGER flybys 1 and 2

Smith, David E. and Zuber, Maria T. and Phillips, Roger J. and Solomon, Sean C. and Neumann, Gregory A. and Lemoine, Frank G. and Peale, Stanton J. and Margot, Jean-Luc and Torrence, Mark H. and Talpe, Matthieu J. and Head, James W. and Hauck, Steven A. and Johnson, Catherine L. and Perry, Mark E. and Barnouin, Olivier S. and McNutt, Ralph L. and Oberst, Jürgen (2010) The equatorial shape and gravity field of Mercury from MESSENGER flybys 1 and 2. Icarus: International Journal of Solar System Studies, 209 (1), pp. 88-100. Elsevier. DOI: 10.1016/j.icarus.2010.04.007.

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Official URL: http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6WGF-4YWXSK4-1&_user=100058&_coverDate=09%2F30%2F2010&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d&_docanchor=&view=c&_acct=C000007338&_version=1&_urlVersion=0&_userid=100058&md5=70f80580d

Abstract

On 14 January and 6 October 2008 the MESSENGER spacecraft passed within 200 km of the surface of Mercury. These flybys by MESSENGER provided the first observations of Mercury from a spacecraft since the Mariner 10 flybys in 1974 and 1975. Data from the Mercury Laser Altimeter (MLA) provided new information on the equatorial shape of Mercury, and Doppler tracking of the spacecraft through the flybys provided new data on the planet’s gravity field. The MLA passes were on opposite hemispheres of the planet and span collectively ˜40% of the equatorial circumference. The mean elevation of topography observed during flyby 1, in the longitude range 0-90°E, is greater than that seen during flyby 2 in the longitude range 180-270°E, indicating an offset between centers of mass and figure having a magnitude and phase in general agreement with topography determined by Earth-based radar. Both MLA profiles are characterized by slopes of ˜0.015° downward to the east, which is consistent with a long-wavelength equatorial shape defined by a best-fitting ellipse. The Doppler tracking data show sensitivity to the gravitational structure of Mercury. The equatorial ellipticity of the gravitational field, C2,2, is well determined and correlates with the equatorial shape. The S2,2 coefficient is ˜0, as would be expected if Mercury’s coordinate system, defined by its rotational state, is aligned along its principal axes of inertia. The recovered value of the polar flattening of the gravitational potential, J2, is considerably lower in magnitude than the value obtained from Mariner 10 tracking, a result that is problematic for internal structure models. This parameter is not as well constrained as the equatorial ellipticity because the flyby trajectories were nearly in the planet’s equatorial plane. The residuals from the Doppler tracking data suggest the possibility of mascons on Mercury, but flyby observations are of insufficient resolution for confident recovery. For a range of assumptions on degree of compensation and crustal and mantle densities, the allowable crustal thickness is consistent with the upper limit of about 100 km estimated from the inferred depth of faulting beneath a prominent lobate scarp, an assumed ductile flow law for crustal material, and the condition that temperature at the base of the crust does not exceed the solidus temperature. The MESSENGER value of C2,2 has allowed an improved estimate of the ratio of the polar moment of inertia of the mantle and crust to the full polar moment (Cm/C), a refinement that strengthens the conclusion that Mercury has at present a fluid outer core.

Document Type:Article
Title:The equatorial shape and gravity field of Mercury from MESSENGER flybys 1 and 2
Authors:
AuthorsInstitution or Email of Authors
Smith, David E.Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Zuber, Maria T.Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Phillips, Roger J.Planetary Science Directorate, Southwest Research Institute, Boulder, CO 80302, USA
Solomon, Sean C.Department of Terrestrial Magnetism, Carnegie Institution of Washington, Washington, DC 20015, USA
Neumann, Gregory A.Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Lemoine, Frank G.Solar System Exploration Division, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
Peale, Stanton J.Department of Physics, University of California, Santa Barbara, CA 93106, USA
Margot, Jean-LucDepartment of Earth and Space Sciences, University of California, Los Angeles, CA 90095, USA
Torrence, Mark H.Stinger Ghaffarian Technologies, Inc., 7701 Greenbelt Road, Suite 400, Greenbelt, Maryland 20770, USA
Talpe, Matthieu J.Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
Head, James W.Department of Geological Sciences, Brown University, Providence, RI 02912, USA
Hauck, Steven A.Department of Geological Sciences, Case Western Reserve University, Cleveland, OH 44106, USA
Johnson, Catherine L.Department of Earth and Ocean Sciences, University of British Columbia, Vancouver, BC, Canada V6T 1Z4
Perry, Mark E.Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA
Barnouin, Olivier S.Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA
McNutt, Ralph L.Space Department, Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723-6099, USA
Oberst, Jürgenjuergen.oberst@dlr.de
Date:September 2010
Journal or Publication Title:Icarus: International Journal of Solar System Studies
Refereed publication:Yes
In Open Access:No
In SCOPUS:Yes
In ISI Web of Science:Yes
Volume:209
DOI:10.1016/j.icarus.2010.04.007
Page Range:pp. 88-100
Publisher:Elsevier
Series Name:Icarus
Status:Published
Keywords:shape, gravity field, Mercury, MESSENGER, flyby, laser altimeter, MLA
HGF - Research field:Aeronautics, Space and Transport (old)
HGF - Program:Space (old)
HGF - Program Themes:W EW - Erforschung des Weltraums
DLR - Research area:Space
DLR - Program:W EW - Erforschung des Weltraums
DLR - Research theme (Project):W - Vorhaben Planetenforschung (old)
Location: Berlin-Adlershof
Institutes and Institutions:Institute of Planetary Research > Planetary Geodesy
Deposited By: Marita Wählisch
Deposited On:10 Jan 2011 09:12
Last Modified:26 Mar 2013 13:25

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