*4.2.3.1 A dense atmosphere and fresh water*

*Mars Exploration - A Step Forward*

*4.2.2 The robotic geologists*

composition of the Martian rocks and soil can be used to infer the ambient conditions under which they are formed, including potential water-related alteration processes. In addition, the rovers were also designed to study the lower layers of the atmosphere to help understand the current Martian weather.

3.**What are the geological characteristics of Mars? What role the wind, water, plaque tectonics, or volcanism have played in the Martian geological history?** Iron compounds, carbonates, clays, salts, and other minerals in which water plays an important role were candidates to answer this kind of questions. Analysis performed on these samples would also help confirm the measurements performed by orbiter missions such as MGS, Mars Odyssey, Mars Express, or the Mars Reconnaissance Orbiter that improved their detec-

4.**Learn how a human exploration mission could be setup.** To study the Martian environment to identify potential risks for humans; and to understand and gather information regarding the chemical nature of the minerals and local resources, to be potentially used for exploitation and use during a manned mission, including course water in any of its forms, as it is the only way to

The Spirit and Opportunity rovers were designed with these questions on mind, considering the rovers as geologists *roving* on the Martian surface, and equipped with a portable laboratory to perform *in situ* analysis of the samples. A 360° panoramic camera (Pancam) and an IR thermal emission spectrometer (Mini-TES) were placed on the rover mast at 1.5 m above the ground. These allowed the optical characterization of the terrain (the geologist eyes) plus a first IR analysis on the potentially interesting targets. In addition, the rovers were equipped with an articulated robotic arm with several tools: a Microscopic Imager (MI) to take closeup images of the samples (the geologist magnifier); the Rock Abrasion Tool (RAT) to allow access to the interior of the rocks (the geologist hammer); and a series of instruments constituting the geologist portable laboratory—the Alpha Particle X-Ray Spectrometer (APXS), the Mossbauer Spectrometer (MS), and a Magnet array for direct analysis of the samples (another Magnet array was placed on the rover chassis to passively analyze the powder depositing on them). The rovers were also equipped with navigation (NavCams) and Hazard Avoidance (HazCams)

tion capabilities with the help of the MER rovers.

ensure long-term manned missions on the Martian surface.

cameras to facilitate a safe roving capability of these robotic geologists.

The MER rovers landed on Mars at the beginning of 2004, during the last days of the southern summer. The soft landings were achieved by means of airbags, with which the rovers bounced very long distances along the Martian surface for a period of time much longer than expected. Spirit landed on January 4, 2004 in the Gusev crater (14.572° S, 175.478° E). Three weeks later, on January 25, Opportunity landed inside a 20-m diameter crater in Terra Meridiani (1.946° S and 354.473° E) in the

MER rovers' journey on the Martian surface is one of the greatest successes among all the planetary exploration missions. From an engineering perspective, the results are impressive: rovers were designed for a 90-sol nominal mission and to rove up to 600 m. However, both rovers operated successfully for years (Spirit

*4.2.3 A journey through the Martian geology*

opposite side of the planet.

**98**

First Opportunity success was its initial lucky-shot, landing inside the Eagle crater, where it performed analysis for 2 months. It detected hematite, which was a clear indicator of a past presence of water in the area, as it is formed in water environments. However, it was also deduced that the water presence was salty and with low pH (so not optimal for life thriving due to the water acidity), with this area probably being a coast region with tidal waters [26]. Later in December 2011, Opportunity also detected other evidences of liquid water in the Martian past. In the Endeavor crater, the instruments detected veins of gypsum (calcium sulfate) inside some rocks. This hydrated mineral was probably formed by water flowing through cracks in the rocks, where the calcium was left behind [27]. Before that, in October 2005, while analyzing the Comanche outcrop by MS, APXS and Mini-TES, the Spirit rover identified rocks formed by key chemical elements such as magnesium and iron carbonates, in proportions up to 10 times higher than the previous analysis on Mars [28]. This discovery was evidence that the Martian past had warmer and wetter areas, with a thick atmosphere and with neutral pH values that are required for the formation of these carbonates. These conditions would potentially favor the existence of some kinds of microscopic life compared to any of the previous analysis performed on the Martian surface.
