**4. Mobile surface missions: from Pathfinder to Curiosity**

Twenty years had to pass before the world looked again toward Mars after the successful Viking missions. The emotional slump caused by the difficulties in finding life on Mars, together with the slowing down of the space race due to the clear leadership of the US after the Viking program, was among the causes of this lack of interest. However, after this time, NASA recovered the impulse considering the new geopolitical scenario in which the study of the Solar System was not anymore a race between countries, but a joint effort among all of them. This way, Europe, Japan, and even Russia were considered as potential allies in this new era of exploration. It is in this framework that the NASA Mars Exploration Program (MEP) [18] kicks-off in 1993. This program laid an ambitious strategy for 1993–2020, with the idea of using all the available launch windows with subsequent missions to study Mars, its climate and geology, available resources for *in situ* exploitation, and the search for life. The original path planned a (now we now) quite optimistically sample-return missions for the decade of 2000, continuing with manned missions to the red planet before 2020.

Understanding the evolution of our neighbor Mars, with which Earth shares a common geological origin, and a similar habitability in their origins 4000 million years ago, is the main objective of the MEP program, the greatest effort for the exploration of the Solar System since the Apollo missions. One of the MEP key characteristics has been the focus on the development of technologies that provide security and reliability on the Martian missions. This has resulted in a high success rate, which has pumped an increasingly great and continuous scientific understanding of Mars. A timeline showing the roadmap for the exploration of Mars can be found in **Figure 1**.

Such an ambitious program requires interdisciplinary collaboration with the Planetary and Martian scientific community, which is done through the Mars Exploration Program Analysis Group (MEPAG)—a scientific group formed by international experts from the main national space agencies around the world; but also MEP interacts closely with the NASA Human Exploration Operation Mission

**95**

*Evolution of the Scientific Instrumentation for* In Situ *Mars Exploration*

Directorate (HEMD) and the Space Technology Mission Directorate (STDM), as

As part of this plan, the MEP objectives are updated as necessary with the new scientific discoveries, while considering the following priority aspects: (1) a continued effort for the development of reliable technologies to improve the analytical capabilities with new and more ambitious scientific instruments; (2) a technological evolution to allow for better and safer technologies for entry, descent, and landing (EDL) in order to be able to land more equipment smoother, and with higher confidence and accuracy; and (3) to keep a reliable and continued network of communication relays, by maintaining a sufficient network of orbiters as the best way to facilitate a sustained flow of scientific discoveries around Mars. This approach allows for better instruments, placed with higher accuracy and safety,

while ensuring a data flow between Earth and the Martian robots [20].

In order to meet these objectives, MEP has successfully combined orbital and surface missions as needed. On the one hand, orbital missions have provided climate and atmosphere compositional studies, combined with mapping and surface characterization activities to facilitate future landing sites. But they also have served to analyze the planetary characteristics such as magnetic field and solar particle interaction, while fulfilling the communications link with Earth for the surface missions. Successful orbiter missions to date have been the Mars Global Surveyor (MGS) in 1996; Mars Odyssey (ODY) in 2001; Mars Express (MEX), a European mission lead by ESA in 2003; Mars Reconnaissance Orbiter (MRO) in 2005; Maven (MVN) in 2013; and the ExoMars Trace Gas Orbiter (TGO), also from ESA, in 2016. On the other hand, lander surface missions were proposed to answer maybe more concrete scientific objectives: the Mars Pathfinder (MPF) in 1997, basically a technological demonstrator also equipped with a small rover; Phoenix (PHX) in 2007, which looked for the presence of ice in high latitudes; and Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) in 2018, mainly

But the true heroes, those missions that have harvested the greatest scientific and public relations success are the exploration rovers. Sojourner is the Mars Pathfinder mission rover in 1997; Spirit and Opportunity are the Mars Exploration

*DOI: http://dx.doi.org/10.5772/intechopen.93377*

covered by NASA's 2014 Strategic Plan [19].

*Key elements and timeline of the robotic and human exploration of Mars.*

**Figure 1.**

dedicated to the study of the planet seismology.

*Evolution of the Scientific Instrumentation for* In Situ *Mars Exploration DOI: http://dx.doi.org/10.5772/intechopen.93377*

#### **Figure 1.**

*Mars Exploration - A Step Forward*

Finally, the key to the mission was the Viking experiment aimed at answering the question of whether Mars might have harbored life in the past or even if there was life present in the soil. In order to do so, Viking included the "biological experiment" consisting of three different instruments: a pyrolitic release (PR), labeled release (LR), and gas exchange (GEX). All these instruments incubated samples extracted from the Martian surface, applying different ambient conditions during several days. In general, the search for organic traces were negative in five out of the six experiments. The remaining one, however, performed by the LR instrument on Viking 2, obtained a positive result [17]. Revolutionary at the beginning, this result was always surrounded by controversy regarding the goodness of the experiment, resulting in serious doubts on the existence of this positive biological response. This controversy is still in force, though the general scientific position nowadays lean the scales toward a false positive result. Even if with controversial or unsatisfactory results, the Viking missions were a great success for the study of Mars, also leaving very important lessons learnt for the generations to come, especially when coming down to looking for alien life or life-tracers. On the one hand, habitable is not the same as inhabited; on the other hand, positively certifying the existence of life requires either repetitive results, and/or a very good assurance that the organic/biological detection is coming from the extraterrestrial source, in order to avoid potential controversies on the results. This might be one reason why, since 1976, no Mars mission has been intended

to look for life on Mars, but to look for conditions of habitability.

**4. Mobile surface missions: from Pathfinder to Curiosity**

Twenty years had to pass before the world looked again toward Mars after the successful Viking missions. The emotional slump caused by the difficulties in finding life on Mars, together with the slowing down of the space race due to the clear leadership of the US after the Viking program, was among the causes of this lack of interest. However, after this time, NASA recovered the impulse considering the new geopolitical scenario in which the study of the Solar System was not anymore a race between countries, but a joint effort among all of them. This way, Europe, Japan, and even Russia were considered as potential allies in this new era of exploration. It is in this framework that the NASA Mars Exploration Program (MEP) [18] kicks-off in 1993. This program laid an ambitious strategy for 1993–2020, with the idea of using all the available launch windows with subsequent missions to study Mars, its climate and geology, available resources for *in situ* exploitation, and the search for life. The original path planned a (now we now) quite optimistically sample-return missions for the decade of 2000, continuing with manned missions to the red planet before 2020. Understanding the evolution of our neighbor Mars, with which Earth shares a common geological origin, and a similar habitability in their origins 4000 million years ago, is the main objective of the MEP program, the greatest effort for the exploration of the Solar System since the Apollo missions. One of the MEP key characteristics has been the focus on the development of technologies that provide security and reliability on the Martian missions. This has resulted in a high success rate, which has pumped an increasingly great and continuous scientific understanding of Mars. A timeline showing the roadmap for the exploration of Mars can be

Such an ambitious program requires interdisciplinary collaboration with the Planetary and Martian scientific community, which is done through the Mars Exploration Program Analysis Group (MEPAG)—a scientific group formed by international experts from the main national space agencies around the world; but also MEP interacts closely with the NASA Human Exploration Operation Mission

**94**

found in **Figure 1**.

*Key elements and timeline of the robotic and human exploration of Mars.*

Directorate (HEMD) and the Space Technology Mission Directorate (STDM), as covered by NASA's 2014 Strategic Plan [19].

As part of this plan, the MEP objectives are updated as necessary with the new scientific discoveries, while considering the following priority aspects: (1) a continued effort for the development of reliable technologies to improve the analytical capabilities with new and more ambitious scientific instruments; (2) a technological evolution to allow for better and safer technologies for entry, descent, and landing (EDL) in order to be able to land more equipment smoother, and with higher confidence and accuracy; and (3) to keep a reliable and continued network of communication relays, by maintaining a sufficient network of orbiters as the best way to facilitate a sustained flow of scientific discoveries around Mars. This approach allows for better instruments, placed with higher accuracy and safety, while ensuring a data flow between Earth and the Martian robots [20].

In order to meet these objectives, MEP has successfully combined orbital and surface missions as needed. On the one hand, orbital missions have provided climate and atmosphere compositional studies, combined with mapping and surface characterization activities to facilitate future landing sites. But they also have served to analyze the planetary characteristics such as magnetic field and solar particle interaction, while fulfilling the communications link with Earth for the surface missions. Successful orbiter missions to date have been the Mars Global Surveyor (MGS) in 1996; Mars Odyssey (ODY) in 2001; Mars Express (MEX), a European mission lead by ESA in 2003; Mars Reconnaissance Orbiter (MRO) in 2005; Maven (MVN) in 2013; and the ExoMars Trace Gas Orbiter (TGO), also from ESA, in 2016.

On the other hand, lander surface missions were proposed to answer maybe more concrete scientific objectives: the Mars Pathfinder (MPF) in 1997, basically a technological demonstrator also equipped with a small rover; Phoenix (PHX) in 2007, which looked for the presence of ice in high latitudes; and Interior Exploration using Seismic Investigations, Geodesy and Heat Transport (InSight) in 2018, mainly dedicated to the study of the planet seismology.

But the true heroes, those missions that have harvested the greatest scientific and public relations success are the exploration rovers. Sojourner is the Mars Pathfinder mission rover in 1997; Spirit and Opportunity are the Mars Exploration Rovers (MER) from 2003, which surprised the world with amazing science for 15 years (while they were designed to last for a nominal mission of 90 sols); and finally, the Curiosity rover, or Mars Science Laboratory (MSL) in 2012, deploys the most complete analytical laboratory ever on another planetary body beyond Earth.

#### **4.1 First orbiters and Pathfinder; 1996: technological readiness**

The first steps of the MEP were not easy. Early years of the program were marked by a number of sounding failures: Mars Observer, in 1992, an orbiter, was NASA's first mission for Martian exploration after the Viking project, and lost communications before entering into orbit; and the Mars Climate Orbiter, in 1998, crashed against the planet surface. But not only NASA had problems, other countries either: The Soviet Union lost Phobos 1 and had a limited success with Phobos 2 in 1988. The Mapc 96 in 1996 was also lost. Japan never arrived to Mars with the Naomi mission in 1999.

Not only the technological issues were a concern during the decade of the 1990s but also the geo-economic situation made it difficult to justify missions with the cost and size of previous decades. This way, the Mars Environmental Survey (MESUR) Pathfinder mission was conceived inside the low-cost planetary Discovery Missions program. This was a new mission concept by NASA grounded in the "faster, better, and cheaper" paradigm. However, an unexpected ally appeared with this mission to gain the popularity and acceptance of the US and world public opinion: Internet. On July 4, 1997, the Pathfinder landing was forecasted through Internet, reaching unprecedented records of visits to the Webpages offering information about the mission. NASA called it "the day Internet stood still." From that experience, NASA understood that in order to win the public opinion favor in order to get acceptance on this new era of planetary exploration, public relations activities advertising all aspects of the missions were key to feed a public avid of this kind of information. And Internet was the perfect means of transmission, allowing almost real-time updates on the missions.

This framework helped restart the exploration of Mars, paving the way for a new generation of planetary exploration missions by the US. The low-cost discovery missions such as Pathfinder had the clear objective of demonstrating the technological readiness to land and explore on Mars, investing only three years and with a low cost: safe landing systems, new communications, the use of modern sensors and image devices, etc., but above all, to demonstrate the capability of maneuvering in the Martian surface with a rover.

The Mars Pathfinder landed softly on Ares Vallis (19.33 N, 33.55 W), on Chryse Planitia (already visited by Viking 1). The lander was named Carl Sagan Memoria Station (after the famous astronomer Carl Sagan); and the rover was called Sojourner (in honor to the American civil rights activist Sojourner Truth). Sojourner was the first rover ever to be successfully deployed outside the Earth-Moon system (after the failure of Mapc 3 in 1971, the Soviet Union sent two rovers to the moon surface later in the decade of the 1970s as part of the Lunokhod program). The surface bi-dimensional planetary exploration era was started.

Even though the mission was basically considered as a technological demonstrator, it included several instruments as part of the platform and rover payloads. The lander's main objective was not only to help on the rover operations but also to work as a meteorological station and to investigate the magnetic properties of the Martian powder. The meteorological observations were done by the Atmospheric Structure Instrument/Meteorology Package (ASI/MET). Deployed on the platform mast, it included several temperature, wind, and pressure sensors. The observations performed during the 80 operative sols of the Pathfinder showed daily pressure variations of 0.2–0.3 mbar, with two complete cycles, correlated with the temperature

**97**

*Evolution of the Scientific Instrumentation for* In Situ *Mars Exploration*

ment [22], raising new scientific questions about their formation.

are needed for the formation of this kind of rocks [24, 25].

the path for the exploration of Mars: water was the key.

variations observed during the Martian day. The temperature observed during the equatorial summer ranged from 263 to 197 K in the day/night cycles. The winds also followed daily patterns, being able to detect some dust-devil episodes as well. All the results were in agreement with those measured 21 years before by the Viking 1 [21]. The magnetic analysis of the Martian powder by the Magnetic Properties Investigation (MPI) experiment showed that the detected iron oxides (Fe2O3, in its phase gamma-maghemite) could be used to infer their water-related formation. However, a higher-than-expected (compared to Earth environment) abundance of goethite (alpha-FeOOH) and hematite (alpha-Fe2O3) was detected by this instru-

The images acquired by the Pathfinder lander Imager for Mars Pathfinder (IMP) instrument were used to contextualize the images by the Sojourner rover, and these also showed a complex surface with rims and canals clearly weathered by fluvial, eolian, and impact processes. Also, some atmospheric processes such as the forma-

The Sojourner rover was equipped with an Alpha Proton X-Ray Spectrometer (APXS) devoted to analyze the composition and atmospheric and water-related weathering of the surface materials from a geochemical perspective. The results showed rock compositions similar to the ones present in the Earth crust (as well as in the SNC meteorites). Thanks to this, it was inferred that volcanic processes were present in the planet geological history, as mafic components and volcanic gasses

After the success of the Pathfinder mission in 1996, NASA's Mars Odyssey was successfully set in orbit around Mars in 2001. The next launch window in 2003 placed ESA's Mars Express (MEX) in orbit, but saw the failure of the Beagle 2 lander after being unable to completely deploy its solar panels. This window was also selected by NASA to launch the most ambitious scientific mission to date: the Mars Exploration Rover (MER). This mission was intended to land two twin rovers, Spirit and Opportunity, on opposite points of the planet, in order to answer a set of scientific questions following the motto *follow the water*. The experience and results gained by NASA and the scientific community with the Pathfinder mission marked

The questions that the MER missions were to address could be summarized as

1.**Was life ever present on Mars?** Assuming life as what we know, the presence of stable liquid water is needed for long periods of time on the planet surface. The presence of water, then, increases the probabilities (though it is not necessarily essential) of harboring life. In this sense, and even that the rovers were not equipped to directly detect life even if present, they were capable of performing mineralogical analysis that would help deduce the formation and evolution conditions of the analyzed materials. So, the search for minerals formed or evolved in water-related processes (precipitation, sedimentation, evaporation, hydrothermal processes, etc.) was priority for the MER rovers.

2.**What are the current weather conditions on Mars? What were they like in the past and why did they change?** Again, the mineralogical analysis of the

*DOI: http://dx.doi.org/10.5772/intechopen.93377*

tion of clouds were observed [23].

**4.2 MER, 2003+2003: follow the water**

*4.2.1 The mission objectives*

follows:

#### *Evolution of the Scientific Instrumentation for* In Situ *Mars Exploration DOI: http://dx.doi.org/10.5772/intechopen.93377*

*Mars Exploration - A Step Forward*

Naomi mission in 1999.

in the Martian surface with a rover.

Rovers (MER) from 2003, which surprised the world with amazing science for 15 years (while they were designed to last for a nominal mission of 90 sols); and finally, the Curiosity rover, or Mars Science Laboratory (MSL) in 2012, deploys the most complete analytical laboratory ever on another planetary body beyond Earth.

The first steps of the MEP were not easy. Early years of the program were marked by a number of sounding failures: Mars Observer, in 1992, an orbiter, was NASA's first mission for Martian exploration after the Viking project, and lost communications before entering into orbit; and the Mars Climate Orbiter, in 1998, crashed against the planet surface. But not only NASA had problems, other countries either: The Soviet Union lost Phobos 1 and had a limited success with Phobos 2 in 1988. The Mapc 96 in 1996 was also lost. Japan never arrived to Mars with the

Not only the technological issues were a concern during the decade of the 1990s but also the geo-economic situation made it difficult to justify missions with the cost and size of previous decades. This way, the Mars Environmental Survey (MESUR) Pathfinder mission was conceived inside the low-cost planetary Discovery Missions program. This was a new mission concept by NASA grounded in the "faster, better, and cheaper" paradigm. However, an unexpected ally appeared with this mission to gain the popularity and acceptance of the US and world public opinion: Internet. On July 4, 1997, the Pathfinder landing was forecasted through Internet, reaching unprecedented records of visits to the Webpages offering information about the mission. NASA called it "the day Internet stood still." From that experience, NASA understood that in order to win the public opinion favor in order to get acceptance on this new era of planetary exploration, public relations activities advertising all aspects of the missions were key to feed a public avid of this kind of information. And Internet was the perfect means of transmission, allowing almost real-time updates on the missions. This framework helped restart the exploration of Mars, paving the way for a new generation of planetary exploration missions by the US. The low-cost discovery missions such as Pathfinder had the clear objective of demonstrating the technological readiness to land and explore on Mars, investing only three years and with a low cost: safe landing systems, new communications, the use of modern sensors and image devices, etc., but above all, to demonstrate the capability of maneuvering

The Mars Pathfinder landed softly on Ares Vallis (19.33 N, 33.55 W), on Chryse Planitia (already visited by Viking 1). The lander was named Carl Sagan Memoria Station (after the famous astronomer Carl Sagan); and the rover was called Sojourner (in honor to the American civil rights activist Sojourner Truth). Sojourner was the first rover ever to be successfully deployed outside the Earth-Moon system (after the failure of Mapc 3 in 1971, the Soviet Union sent two rovers to the moon surface later in the decade of the 1970s as part of the Lunokhod program). The surface bi-dimensional planetary exploration era was started.

Even though the mission was basically considered as a technological demonstra-

tor, it included several instruments as part of the platform and rover payloads. The lander's main objective was not only to help on the rover operations but also to work as a meteorological station and to investigate the magnetic properties of the Martian powder. The meteorological observations were done by the Atmospheric Structure Instrument/Meteorology Package (ASI/MET). Deployed on the platform mast, it included several temperature, wind, and pressure sensors. The observations performed during the 80 operative sols of the Pathfinder showed daily pressure variations of 0.2–0.3 mbar, with two complete cycles, correlated with the temperature

**4.1 First orbiters and Pathfinder; 1996: technological readiness**

**96**

variations observed during the Martian day. The temperature observed during the equatorial summer ranged from 263 to 197 K in the day/night cycles. The winds also followed daily patterns, being able to detect some dust-devil episodes as well. All the results were in agreement with those measured 21 years before by the Viking 1 [21].

The magnetic analysis of the Martian powder by the Magnetic Properties Investigation (MPI) experiment showed that the detected iron oxides (Fe2O3, in its phase gamma-maghemite) could be used to infer their water-related formation. However, a higher-than-expected (compared to Earth environment) abundance of goethite (alpha-FeOOH) and hematite (alpha-Fe2O3) was detected by this instrument [22], raising new scientific questions about their formation.

The images acquired by the Pathfinder lander Imager for Mars Pathfinder (IMP) instrument were used to contextualize the images by the Sojourner rover, and these also showed a complex surface with rims and canals clearly weathered by fluvial, eolian, and impact processes. Also, some atmospheric processes such as the formation of clouds were observed [23].

The Sojourner rover was equipped with an Alpha Proton X-Ray Spectrometer (APXS) devoted to analyze the composition and atmospheric and water-related weathering of the surface materials from a geochemical perspective. The results showed rock compositions similar to the ones present in the Earth crust (as well as in the SNC meteorites). Thanks to this, it was inferred that volcanic processes were present in the planet geological history, as mafic components and volcanic gasses are needed for the formation of this kind of rocks [24, 25].

## **4.2 MER, 2003+2003: follow the water**

After the success of the Pathfinder mission in 1996, NASA's Mars Odyssey was successfully set in orbit around Mars in 2001. The next launch window in 2003 placed ESA's Mars Express (MEX) in orbit, but saw the failure of the Beagle 2 lander after being unable to completely deploy its solar panels. This window was also selected by NASA to launch the most ambitious scientific mission to date: the Mars Exploration Rover (MER). This mission was intended to land two twin rovers, Spirit and Opportunity, on opposite points of the planet, in order to answer a set of scientific questions following the motto *follow the water*. The experience and results gained by NASA and the scientific community with the Pathfinder mission marked the path for the exploration of Mars: water was the key.

#### *4.2.1 The mission objectives*

The questions that the MER missions were to address could be summarized as follows:


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.

