I have a map tile package for some data for Mars in GCS_Mars_2000_Sphere. I have uploaded it to my ArcGIS Online Basic account after creating it using the default settings and zoom extents used in ArcGIS / Google / Bing. After it uploads and I add it as a basemap, however, it retains earthly dimensions. The distances between features are incorrect. This isn't a projection issue because those dimensions still exist when the same map tile package is added as a base layer to a globe scene. The distances are off by nearly 100%. One mile on my map is actually only 0.53 miles on the real landscape. My understanding is this is because ArcGIS Online automatically converts it to WGS84 Web Mercator. How can I publish/upload this map tile package to ArcGIS Online and retain the correct size and shape of the planet so that measurements are accurate?