Orcus Patera (Natural Colors; credits: Dr Paolo C. Fienga - Lunexit Team)

Caption ESA:"Orcus Patera is an enigmatic elliptical depression located between Elysium and Olympus Mons.

This well-defined depression extends approximately 380 by 140 Km in a N/NE–S/SW direction. It has a Rim that rises up to 1800 mt above the surrounding Plains, while its Floor lies 400–600 mt below the surroundings. The term ‘Patera’ is used for deep, complex or irregularly shaped Volcanic Craters such as the Hadriaca Patera and Tyrrhena Patera at the N/E margin of the Hellas Impact Basin.

However, despite its name and the fact that it is positioned near Volcanoes, the actual origin of Orcus Patera still remains unclear".