What we already know about water and potential traces of life on Mars
When you look at an image of Mars, you’re struck by the resemblance to Earth. It’s easy to recognize the remains of lakes, rivers, deltas. The Earth and Mars share a common past : when they formed in the accretionary disc around the Sun 4.5 billion years ago, Mars and Earth were "magma" planets that slowly cooled until liquid water appeared on their surfaces in the form of lakes and oceans. But while our planet maintained its oceans and allowed life to flourish, Mars dried up to become the cold, dry world we see today - a divergence of fates that dates back about 3 billion years. Since the oldest traces of life on Earth date back about 3.7 billion years, when the two planets had not yet evolved in a differentiated manner, it is believed that favourable conditions for the appearance of life on Mars existed.
Since the early 2000s, a significant number of space missions in orbit or on the surface of Mars have provided valuable information. This vast programme of study of the planet is structured around three scientific axes : determining whether life may have emerged, understanding the processes and history of climate, and understanding the evolution of the planet’s surface and interior.
American missions such as Mars Odyssey and Mars Reconnaissance Orbiter, as well as the European Mars Express mission, have made it possible, among other things, to map hydrated minerals, carbonates and sulphates, for example, to analyse the surface and interior of the polar ice caps and to study atmospheric processes highlighting the water or dust cycle that contributes to atmospheric processes.
The habitability of a planet, a key concept
These first clues are an important first step towards the notion of Mars’ habitability. The term habitability refers to the fact that a planet has been able to bring together at some point in its history all the favourable conditions for the appearance of life. Even if the clues gathered by the first missions gave hope to the Martian scientific community that life could have emerged on this planet, they are not enough to demonstrate this. Based on what is known on Earth, and even if it is not the only possible model, we consider that the proof could be made if several parameters are gathered in the same place, and at the same geological time. These parameters include the presence of saline liquid water with a moderate pH over a long geological period, the presence of an energy source to initiate chemical reactions, the presence of organic materials and biosignatures. In addition, in order to be able to observe the biosignatures today, the biosignatures must have been preserved from biodegradation due, for example, to fossilization processes or cosmic radiation.
In August 2012, the American Mars Sample Laboratory mission landed the famous Curiosity rover on Mars. This rover carrying ten scientific instruments, including two French ones, has the mission to demonstrate the habitability of the landing site, to characterize the geology of the landing site and the climate of Mars. The site chosen for the mission, Gale Crater, is an impact crater dated between 3.8 and 3.5 billion years ago with the presence of sedimentary layers indicating the past presence of a large quantity of liquid water. Thanks to all its instruments, this mission is a great success as it has now demonstrated the habitability of the site. However, these results raise new questions about the Gale Crater itself : how long has it remained habitable ? Is it the only crater on Mars to have been habitable ? More generally : why has habitability stopped ? And above all, habitability does not necessarily mean that life really existed : did life develop on Mars at some point in its history ?
An ambitious plan : bringing back samples containing biosignatures
The next American mission to the planet Mars, named Mars2020, will again land on Mars a rover similar to Curiosity and named Perseverance, the size of a small car, carrying seven instruments including a French instrument. The launch is scheduled for July 2020 and the landing in the Jezero crater is scheduled for February 2021. The main objective this time is the preparation for the return of samples of traces of fossil life. All the rover instruments will identify the best samples likely to contain biosignatures. Thanks to its motorized arm, some forty samples will be taken and placed in containers left on site. The next mission, currently being programmed, will collect them and bring them back to Earth for laboratory analysis. The Jezero landing site has been carefully chosen to optimise the chances of finding biosignatures. It is again an impact crater of the same age as Gale. It shelters a clay delta rich in hydrated minerals, indicating the presence of a large amount of liquid water in the past.
Among the 7 scientific instruments of the Mars2020 mission is the SuperCam instrument developed jointly by a group of French and American laboratories, universities and industrials. A veritable Swiss army knife, this instrument combines several techniques allowing the analysis of the chemical composition of rocks by the LIBS technique which uses a laser to pulverize them, the analysis of minerals and organic matter by the RAMAN technique which analyses the light emitted by the vibrations of molecules excited by a laser, or passive visible and infrared spectroscopy. A context camera will allow to see the analysed areas in detail : for example an area shot with the laser or interesting mineralogical veins. Finally, a microphone will be used to record sounds. All these techniques contribute to mineralogical field analysis. They are complementary. If the area observed is suitable, other instruments of the mission will also perform analyses, all of which will be used to identify interesting samples to bring back to Earth.
SuperCam is the successor to the ChemCam instrument, which was on board the Curiosity rover. It has been greatly improved and will contribute to the scientific objectives of the mission.
With the Mars2020 mission and the sample return from the next mission, we are on the verge of discovering for the first time that a planet other than our own could have supported the development of life in its history. The Earth and Mars are just two small planets orbiting a common star on the periphery of a galaxy made up of hundreds of billions of stars, mostly planets, among hundreds of billions of galaxies. So the search for life in our solar system and in the universe has only just begun.
Source : https://theconversation.com/une-nouvelle-camera-pour-traquer-des-traces-de-vie-sur-mars-132784