The landing of NASA’s rover Perseverance in February 2021, then the Chinese space agency’s Zurong landing in May 2021 increased the number of motorized vehicles on the surface of the Red Planet.

Today there are six mobile vehicles on the surface of Mars called rovers – Sojourner, Spirit, Opportunity, Curiosity, Perseverance, Zurong – of which only three are in operation. The first five have been deployed to the surface of Mars by NASA since the late 1990s and have just been joined by the rover from the Chinese mission Tianwen-1. The latter is a geological rover, and will better understand the composition and rocks of the Red Planet. Persevering, he launched a spectacular epic: to bring a little Mars back to Earth.

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Read more: March 2020 begins formidable search for Mars samples

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Back to the future, to understand why these missions are built like this and the future of Mars exploration.

The Ancestors of Rovers Are Definitive Probes, “Landers”

The first probe to successfully land on the surface of Mars had two stationary landers called “Vikings” from the mission of the same name. They landed in 1976. The mission, spearheaded by Carl Sagan, one of the founders of Exobiology, had strong ambitions, as it aimed to explore the biological activities associated with bacterial life on the surface of March.

Unfortunately, despite its technical success, measurements made by the Viking probe did not make it possible to uncover such signatures. On the other hand, they provided the first measurements on surface conditions, specifically meteorological data in several years. These have greatly improved our knowledge of the environment on the surface of Mars, making it possible to prepare for subsequent missions.

Still, a lack of life-related results, along with a series of unsuccessful missions launched to Mars in the 1980s and 1990s, delayed other efforts until 1997.

The first rover landed on Mars at the turn of the 21st century

NASA’s tiny Sojourner robot, the size of a radio-controlled car, was intended to demonstrate the feasibility of controlling and developing a rover on Mars: it was a technical demonstrator. He was carrying only a scientific instrument at the time and had only rolled a few meters on the surface of Mars.

Based on this learning, NASA developed the now famous Mars Exploration Rovers, called Spirit and Opportunity. Spirit and Opportunity surveyed the surface of Mars for several years, beginning in 2004. These vehicles were 1.5 meters long and weighed around 200 kg. The spirit evolved for about 7 years in Gausev Crater and was arrested because it could no longer move and many of its instruments were broken.

Opportunity has operated for nearly 15 years in the field of terra meridian. The latter has traveled more than 45 kilometers across the surface of Mars, which will remain a record for many years to come (or several decades, depending on the longevity of the current rovers). The mission was halted in February 2019 after an unexpected dust storm that did not allow the robot to recharge its batteries through its solar panels.

Mission of Spirit and Opportunity Rovers

One of the great historical missions of the Mars rovers is the study of water on the planet’s surface.

XX. Most of the orbital probes to reach and study Mars in^I The century had observational capabilities allowing imagery and some spectral measurements, but most of the water clues collected from space were geomorphological clues (topographics observed on the surface that may be in relation to fluid flow).

Unfortunately, these observations did not make it possible to know in what period these flows may have occurred, nor their duration. NASA’s Mars Global Surveyor Orbital Probe confirmed this in the late 1990s and also showed that climate change at the surface was complex. But the effect of water on this climate evolution and its interaction with the atmosphere cannot be understood from this type of remote observation. It became necessary to send rovers to obtain information directly on the surface, as close as possible formed by liquid water, or metamorphic rocks.

Spirit and Curiosity have discovered sedimentary rocks and salts that show that at two of the rovers’ exploration sites, which are several thousand kilometers apart, water flows and persists over long periods of time. This suggests that water must have been abundant and widespread on the surface of Mars.

In addition, these rovers showed the importance of being mobile in exploration, as they made discoveries on liquid water outside of their landing site. This eventually convinced NASA, and other space agencies today, that rovers were essential elements in the planet’s surface exploration strategy, despite the greater complexity of development (compared to undercarriage).

Curiosity rover, a symbol of an evolution in the exploration of Mars

In 2004, NASA selected the Mars Science Laboratory mission to send an even more fascinating exploration rover to Mars – Curiosity.

Scientific and exploratory strategies are developing towards the current plan for Mars exploration established by NASA: after studying part of the geology of Mars on the surface, and the existence of perennial liquid water in the past with Mars Exploration Rovers After showing it, Curiosity aimed to show that the surface of Mars could be “habitable”. By this term, we mean that Mars was able to bring together in one place and at the same time the ingredients that we consider necessary for the development of life, namely:

• liquid water,

• a form of energy,

• and essential components for making organic materials. The most symbolic are organic molecules, but we must not forget minority components such as phosphorus for example.

This term of habit, in “conditional”, means that if these conditions are met, they are not sufficient to guarantee that life necessarily arises.

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Read more: Meet the rovers searching for signs of life on Mars

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So Curiosity’s main objective was to show whether Gale Crater, to which the rover was sent, could be habitable. If we knew that solar power was clearly available, the rover would have had to find past permanent water clues, like the Mars Exploration Rovers, but also to uncover the presence of organic molecules and smaller elements. . For this, Curiosity was built much taller than its predecessors: more than 2 meters high. It has about ten analysis instruments, as well as a system for sampling Martian rocks with a drill operating on the principle of a percussion drill.

Curiosity detects organic matter

In addition, due to its size, the robot uses the electrical energy produced by a small nuclear reactor which allows it to function as it pleases without the recharging of its batteries by solar panels.

Thanks to its exceptional performance, the robot not only revealed several geological and mineralogical indices of the presence of perennial liquid water in craters in the past, but it also enabled the detection of endogenous organic matter, which was sought after. Failed missions since Viking. This material was detected by sample analysis on the Mars instrument – Limitation of experimental conditions on Mars: the analysis method used and the presence of unexpected inorganic compounds in the soil made it possible to detect organic molecules reacting only with inorganic species gave. These reactions produced chlorinated species, including the chlorobenzene symbol of these analytes, and organic sulfur species.

From these species, we try to get back to the true nature of the organic matter present in the sample, but this is a long and tedious task of investigation. What can be said to date, from the analysis of many samples collected on the rover’s route, is that this organic matter is present in very low concentrations in the layer. The surface of the surface from which Curiosity takes samples (within the top 10 centimeters).

This would show the strong influence of conditions prevailing on the Martian surface on the stability of organic materials: the presence of oxidants such as perchlorates and ionizing radiation in amounts on the surface can cause the growth and destruction of these molecules.

However, through this direct detection of organic matter, Curiosity has proved that Gale Crater may have been habitable in the past.

ESA’s future Rosalind Franklin rover will search for deeply buried organic molecules

The European Space Agency, which is developing the ExoMars mission in partnership with the Russian space agency Roscosmos, has decided to drill down to a depth of about 2 meters to search for samples that are theoretically protected from aggressive surface conditions. model. We will know if this is the case only after the first samples are analyzed in 2023, and then we will be able to assess the effect of surface conditions as a function of depth.

In addition, ESA has selected a number of instruments that will provide additional information on the mineral and organic material content of the samples, making it easier to reconstruct the puzzle of the materials present in the samples in case of organic matter detection. ..