Why do some images lean to the right while other lean to the left?
The Mars Odyssey spacecraft follows a polar orbit, but never flies perfectly along the meridian lines nor directly over the poles (+/- 90 latitude). The fact that THEMIS images are usually longer along-track, as compared to their cross-track width, combined with the slightly offset polar orbit, results in images that appear to "lean" when displayed in map projections with north up. Images that appear to lean to the right (like "/") were collected on the descending orbit node; images that appear to lean to the left (like "\") were collected on the ascending orbit node.
Odyssey Extended Mission orbit changes had the effect of changing the local time of each node:
- descending orbit node images collected before orbit 55600 usually have day timestamps (6am-6pm)
- descending orbit node images collected after orbit 55600 usually have night timestamps (<6am or >6pm)