The cartographic lunar reference frame
We describe how lunar cartographic coordinates are currently determined internationally, based on recommendations of the International Astronomical Union (IAU) Working Group on Cartographic Coordinates and Rotational Elements. Currently, a mean Earth/polar axis (ME) system-based frame and ephemeris (JPL DE 421 ME) is used for that purpose. Recently, there has been some discussion that a lunar principal axis system-based frame should be used instead. We describe how that would be a major change to how lunar data are currently acquired, and how data and mapping products are created and archived, searched for, accessed, and used, and our concerns that such a change would cause significant problems. Existing lunar data, data products, papers, and databases could need to be converted, or substantial confusion could result due to the ∼1 km difference between systems, perhaps resulting in navigation or safety issues. The publication and dissemination of any proposal(s) to change systems is encouraged, as are comments on a comparatively much smaller update to the current ME frame proposed here.