The International Astronomical Union’s (IAU) Working Group for Cartographic Coordinates and Rotational Elements (WGCCRE) has the responsibility of defining the rotational elements of the planets, satellites, asteroids, and comets of the Solar System. WGCCRE does this on a systematic basis and relates cartographic coordinates rigorously to the rotational elements.
The WGCCRE issues a report approximately every three years, describing the most up-to-date recommendations for the cartographic coordinates and rotational elements of all planetary bodies. The current report consolidates recommendations made at the 2015 meeting of the IAU and is entitled “Report of the IAU Working Group on Cartographic Coordinates and Rotational Elements: 2015”, published in the journal Celestial Mechanics and Dynamical Astronomy.
The report, available online, provides updated definitions of the latitude and longitude systems and body sizes and shapes for all mapped bodies in the Solar System besides the Earth. This information can be used as a basis for all mapping of these bodies, as well as for navigation purposes in their vicinity, or on their surfaces.
The recommended coordinate system and body size and shape information will be used by planetary science researchers to assign geographic position information to their data sets, so that such information can be registered and compared at known levels of accuracy and precision. This information can then be used by other individual scientists, instrument teams, spacecraft missions, and space agencies to make maps and to geographically register information. The recommendations also allow for the accurate and safe navigation of spacecraft near Solar System bodies.
The chair of WGCCRE, Geodesist Brent Archinal from the United States Geological Survey (USGS) , explains, “Researchers doing data processing can either directly use the information from the tables presented in their own software, or rely on software maintained by others, such as the NASA Planetary Data System Navigation and Ancillary Information node”.
Of particular interest in this report is the adoption by the IAU of new equations describing the orientation of Mars (from Kuchynka et al., 2014), that provide a significant improvement in determining coordinates on Mars over time .
 The USGS Astrogeology Science Center in Flagstaff, AZ has a long history of assisting the IAU with planetary cartography, as well as planetary nomenclature. The USGS Astrogeology Science Center is a national resource for the integration of planetary geoscience, cartography and remote sensing. The centre was established in 1963 to provide lunar geologic mapping for NASA and to assist in training astronauts destined for the Moon. Throughout the years, the USGS has participated in processing and analysing data from numerous missions to planetary bodies in our Solar System, and collaborates with the planning and operation of space exploration missions.
 The previous model recommended by the Working Group has an error of several tens of metres over 20–30 years, while the new model has an error closer to ten metres over such periods. An improvement has also been made in the precision of the definition of longitude on Mars. The small, approximately 500-metre-diameter crater Airy-0 has been used since the early 1970’s to define zero degrees longitude (the prime meridian location) on Mars. However, it is difficult to precisely ascertain the centre of such a crater at the much smaller metre level of current measurements on Mars. So the Working Group has followed the recommendations of Kuchynka et al. (2014) and the NASA Mars Geodesy and Cartography Working Group to fix the longitude of the Viking 1 lander, at 47°.95137 west longitude. This keeps the prime meridian at the approximate centre of Airy-0. However, it provides for metre-level precision in measuring longitude on the Martian surface, with new measurements relative to the Viking 1 lander, whose position has been determined radiometrically relative to other Mars landers and rovers at the metre level.
USGS Geodesist, Chair of the IAU Working Group for Cartographic Coordinates and Rotational Elements
Lars Lindberg Christensen
IAU Press Officer
Garching bei München, Germany
Tel: +49 89 320 06 761
Cell: +49 173 38 72 621