Mars, the Meridian, and Mert: The Quest for Martian Longitude
Abstract
From the mid 1960?s until his passing last year, Merton Davies of RAND was closely involved in establishing and maintaining the fundamental coordinate system for Mars. This included the establishment of the location of a modern 0-degree or Prime Meridian for Mars. In the early 1970's, images of the Martian surface became available via the Mariner 9 spacecraft. In 1973 G. de Vaucouleurs, Davies, and F. Sturms, Jr. proposed (JGR, 78, 4395) that a small easily identifiable crater in the area of Sinus Meridiani - the previously accepted origin - be used to define the Meridian. H. Masursky, de Vaucouleurs, and Davies selected an ~500 m diameter crater to serve this purpose. They proposed a name of Airy-0 for the crater in honor of Sir George Airy, who installed the transit instrument at the Greenwich Observatory, which for many years defined the Prime Meridian of the Earth. In a photogrammetric adjustment of Mariner 9 images Davies (Photo. Eng., 39, 1297; JGR, 78, 4355) held the longitude of Airy-0 fixed at 0-degrees, and thereby tied the entire Martian coordinate system to this crater. Davies and colleagues at RAND continued through 2001 in revising this coordinate system. All the while, these improved coordinate systems continued to be tied to Airy-0 and provided revised values for W0, the angle relating surface longitudes to inertial space coordinates. In 2001, the NASA Mars Geodesy and Cartography Working Group, chaired by T. Duxbury, and having as members many scientists (representing e.g. NASA, USGS, Malin SSS, DLR) interested in Martian coordinate system problems, assessed all available information on the location of Airy-0. This included solutions from Davies and Colvin and others, an evaluation of spacecraft lander locations, a Mars Global Surveyor Mars Orbiter Camera (MOC) image of Airy-0, and MOLA data in the vicinity of Airy-0. A value of W0 = 176.630 degrees was adopted for use, and this value has now in turn been adopted by the IAU (Seidelmann et al., Cel. Mech. and Dyn. Ast., 82, 83) and various Mars missions. It is hoped that this value is accurate to ~100 m and will now be held fixed for many years to come, and it is fitting that Merton Davies contributed substantially toward determining this value.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2002
- Bibcode:
- 2002AGUFM.P22D..06A
- Keywords:
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- 1227 Planetary geodesy and gravity (5420;
- 5714;
- 6019);
- 1229 Reference systems;
- 1243 Space geodetic surveys;
- 1729 Planetology;
- 6225 Mars