*4.3.1 Mission objectives*

*Mars Exploration - A Step Forward*

*4.2.3.5 Ambient and atmospheric conditions*

Mars called Heat Sink Rock [34].

simply overwhelming.

*explore habitability.*

layers of the plateau. These structures are formed on Earth by the rocks falling on soft surfaces, which would confirm the presence of stable water bodies heated up by

In addition to water-related discoveries, both Spirit and Opportunity helped performing many other discoveries and studies to further the knowledge of the red planet. Opportunity became an expert on the geology of Martian craters [31] after visiting more than 100 impact craters, which allowed understanding their formation and erosion on the Martian atmosphere. The Martian environment was monitored as well, studying the cloud formation and the suspended powder and opacity, and how it affected the solar panels of the rovers (curiously, the next rover sent to Mars would be equipped with a nuclear battery instead of being solar-powered). The dust-devils on the surface (firstly detected by the Pathfinder) were photographed by Spirit, and were key for the mission extension, as they helped recovering power for the rovers by cleaning the powder accumulating on the solar panels [32]. A complete temperature profile of the Martian atmosphere was performed by Opportunity, combining Mini-TES data [33] with the Mars Global Surveyor orbiter TES instrument data. Also, Opportunity found the first extra-Martian meteorite on

Spirit and Opportunity rovers were decidedly successful missions that provided prolifically scientific evidences of the past presence of water on the Martian surface among other things. Whichever of those discoveries would have absolutely justified the missions by themselves; but considering MER missions' success all together is

In order to prepare for the missions to come, NASA launched the Mars Reconnaissance Orbiter (MRO) in 2005, with the objective of mapping and facilitating communications. And the *follow the water* motto would be closed after the limited results obtained by the Phoenix lander in 2008, which landed in the polar regions of Mars (68° N latitude), but did not keep up with the very high expectations of this unexplored area. So, once the existence of an ancient wet Mars had been proved, the next milestone in the Martian exploration was to understand if the water presence could facilitate conditions favorable for the appearance of life:

**4.3 Curiosity (MSL) 2011: explore habitability—seek for signs of life**

The foundations laid by the Mars Exploration Program, with communications guaranteed by several orbiters on Mars (ODY, MEX, and MRO were operative in 2012; with two other on their way: MVN and TGO), and the experience gathered during the MER missions in many aspects, including the power source for the rovers, facilitated a science-centered design for the next rover to be operated on Mars. The Mars Science Laboratory (MSL), or Curiosity rover, landed in 2012 with only a small mass dedicated for communications (an UHF antenna) with orbiter relays. It also incorporated a light radioisotope thermoelectric generator (RTG) as a power source, which would also guarantee a stable power source for the rover (contrary to the solar-based power system on the MER). Furthermore, MSL introduced a new landing method based on the famous *sky crane*, which greatly reduced the mass of the entry, descent, and landing (EDL) system, being this mass allocated for the rover itself. This way, on August 5, 2012, the heaviest scientific mobile platform was deployed on Mars, with almost 900 kg of mass devoted to the exploration of the

volcanic activity, which could also be favorable for microscopic life.

**100**

Martian surface.

The Curiosity rover, equipped with the most powerful set of scientific instruments ever on another planetary body, was bound to determine if Mars could have harbored life at any time in its past, as well as continue understanding the role played by the water to this end; of course, it was also prepared to study the Martian climate and geology. So, the new exploration paradigm migrated from *follow the water* to *explore habitability*, by studying the chemical and structural properties of the soil and rocks, especially those presenting water-related formation scenarios.

Contrary to MER, Curiosity included instrumentation capable of performing analysis which can be related to biological studies or processes in order to address the following objectives: the search of organic carbon compounds or biosignatures; geological and geochemical analysis based on the analyzed rocks; analysis of the Martian climate and its evolution; and also to prepare potential future manned missions by being able to characterize the planet radiation on the surface.
