Selecting a landing site for a precious Mars rover to land and roam in is a difficult task.
On the one hand you want as interesting geological terrain to test your science axioms, on the other hand you want the rover to land safely.
The latter means that the actual landing terrain needs to be relatively flat, and flat is not the most interesting geologically speaking. So the flat terrain better be near interesting layered terrain or you will have a rover driving for miles before anything scientific will be able to peek your interest.
These facts are not different for the Mars Science Laboratory as they were for the Mars Exploration Rovers Spirit and Opportunity, 8 years ago. What is different is that we are better at guiding the landing to a precise (relatively speaking) location. (see also our explanation on the Picture of the Day: T-48 days)
How does NASA go about selecting an optimum landing site ?
One criterium next to a safe, flat landing spot is the need of the Science in this particular mission.
For this you have to agree on what the science question is you want to get answered (or : questions, plural) and then start sifting through all the possible landing sites on Mars has that could give you data to determine your answer on.
In the case of MSL we are looking for a particular geologic environment, or set of environments, that could support or could have supported microbial life.
Next the number and kind of science instruments that the rover is equipped with are taken into consideration. More specifically ‘what science test can be done with what instrument on what kind of terrain?
This leads to looking for a landing site with morphologic AND mineralogic evidence of past water. Furthermore, a site with multiple hydrated minerals is preferred. E.g. Hematite (like found at the Spirit landing site) and other iron oxides, sulfate minerals, silicate minerals, silica, and possibly chloride minerals have all been suggested as possible substrates for fossil preservation.
On Earth terrain which contains these minerals are all known to facilitate the preservation of fossils.
And however interesting the terrain, the rover still needs to be able to drive safely on it.
Because of the time it takes the rover to slow down during descent, the rover can not land on a mountain that is too high as that would shorten the Entry, Descent and Landing (EDL) time too much and would leave the engineers with not enough time to deploy parachutes, retrorockets and crane.
Next, the site can not be too cold as the instruments on and in the rover would freeze, as would the engines driving the rover around on Mars.
To get to the right landing site a number of Landing Site workshops are organised. Narrowing down the possible candidates from 33 potential landing sites at the 1st workshop to 6 at the end of the 2nd workshop,
At the 3rd workshop that list was further reduced to 4 landing sites.
It took 2 more workshops to finally select the Gale Crater as the landing site for Curiosity in May 2011
Finally, on July 22, 2011, it was announced that Gale Crater had been selected as the landing site of the Mars Science Laboratory mission.
Today we are showing you the first of these 4 landing sites: Eberswalde Crater, situated in an ancient river delta, 24 degrees south of the Martian equator at an elevation of -1,450 meters (-4,757 ft) below Mars zero-elevation point.
Eberswalde Crater is a partially buried impact crater in Margaritifer Terra, an ancient, heavily cratered region of Mars that is as much as 2600 kilometers wide. The crater is just north of the Holden Crater.
The crater lies just to the north of Holden Crater, a large crater that may have been a lake. The crater was named after the German Town Eberswald in the German Federal State (Bundesland) of Brandenburg, about 50 km northeast of Berlin. Eberswalde crater is only 65.3 kilometers wide (compared to 140 km Gale Crater) and is a good deal more south of the Martian equator: 24°S, 33°W.
Landforms in the crater provide strong evidence of the prior existence of flowing water on Mars.