A nice New Year's post starting the year with a question (and answer!) on the fabulous high resolution stereo camera (HRSC) image of Orcus Patera, first published by ESA (here) in 2010, and reposted as the Image of the Day on 31 December 2011 at the Mars Travel blog. Best wishes to everyone for a healthy and successful 2012. Details below! -- Daniel

First, here's the image (click image to access the original post in ESA web):

 

Orcus Patera is an enigmatic elliptical depression located between the volcanoes of Elysium Mons and Olympus Mons. This well-defined depression extends approximately 380 km by 140 km in a NNE–SSW direction. It has a rim that rises up to 1800 m above the surrounding plains, while the floor of the depression lies 400–600 m 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 north-eastern 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 remains unclear.Credits: ESA/DLR/FU Berlin (G. Neukum)

  Click for hi-res version

Orcus Patera is an enigmatic elliptical depression near Mars’s equator, in the eastern hemisphere of the planet. Located between the volcanoes of Elysium Mons and Olympus Mons, its formation remains a mystery. Often overlooked, this well-defined depression extends approximately 380 km by 140 km in a NNE–SSW direction. It has a rim that rises up to 1800 m above the surrounding plains, while the floor of the depression lies 400–600 m below the surroundings.

Earlier today, Mars Travel blogger David Geaney sent in a question: 

If you look at one of the central craters in Orcus Patera using the HRSC image, you will see there is something blue in the crater. What is the blue material? Thank you for your time and patience.

We passed the query to Mars Express project scientist Olivier Witasse, who wrote:

Hi David,

The blue is not a lake....

It's dust, which emits in the blue part of the spectrum. In the data processing, the blue part is somewhat enhanced, which sometimes creates a wrong impression.

Cheers,

--Olivier