Humans have been undertaking missions to explore the planet Mars since the 1960s. Following its launch on 28 November 1964, NASA’s Mariner 4 probe was the first to fly by Mars on 14 July 1965. To this day, four space agencies have completed missions to investigate the red planet: NASA (the National Aeronautics and Space Administration), ISRO (the Indian Space Research Organisation), the Soviet Union and Russia’s space programme and the ESA (European Space Agency).

During the 1960s and at the start of the 1970s, several probes were sent to fly by Mars. The most successful mission was that of NASA’s Mariner 9 probe, launched at the end of 1971. Mariner 9 remained in orbit around Mars for almost one year and was able to take over 7,000 photos of Mars, which radically changed our perception of this planet.

Finally, in 1975, NASA sent two pairs of orbiters and landers. An orbiter is a space probe that orbits a celestial body whereas a lander refers to a spacecraft intended to touch down on the surface of a celestial body. Viking 1 and Viking 2 touched down on Mars and remained there for several years. Unfortunately, they did not find any clear sign of life on Mars.

At the end of the 1990s, a complete map of Mars, from the north to the south pole, was established by Mars Global Surveyor, a NASA orbiter. Almost simultaneously, NASA launched the Mars Pathfinder, which consisted of a lander and a rover, the famous Sojourner. This is the first rover to have functioned outside of the Earth or the Moon. A rover is a motorised vehicle designed to move around on the surface of a planet or a moon (contrary to a lander which remains immobile once it has landed on a celestial body.) For a complete classification of the different spacecraft, please consult this explanatory page provided by the NASA.

The Mars Odyssey orbiter, which is still in orbit around Mars, was launched by NASA in 2001. In 2003, the ESA sent a mission to Mars that consisted of an orbiter and a lander, called Mars Express and Beagle. The lander was unfortunately lost during the landing, but the orbiter is still on its mission.

In 2004, NASA sent two other rovers to Mars: Spirit and Opportunity. Spirit broke in a sand dune in 2010, whereas Opportunity survived until 2018, when it stopped functioning during a sand storm.

In 2006, another NASA orbiter, the Mars Renaissance Orbiter, was put into orbit. Since then, it has sent us more data about Mars than all of the other missions combined. One year later, NASA sent the Mars Phoenix, another stationary lander. Unfortunately, NASA lost contact with it after a few months and declared it dead in 2010.

A new NASA rover, much more powerful than all the others, the Curiosity, arrived on Mars in 2012. The design of Curiosity inspired the development of the rover Perseverance, which landed on Mars in February 2021. One of Perseverance’s main missions is to collect samples from the surface of Mars. It is expected to bring these samples back to Earth in 2031, as part of a joined mission between NASA and the ESA. The latest news from Perseverance is available on the following page.

Finally, let’s not forget the ExoMars mission, a collaboration between the ESA and the Russian space agency Roscosmos. The mission contains a lander, called Schiaparelli, which was sent to Mars in 2016 but broke during the landing, and an orbiter, called Trace Gas Orbiter, sent in the same year and which is still there. This same mission also planned to send a rover in 2022, named Rosalind Franklin. For the ESA, research and science are aspects that are central to the human condition, as name sponsorship should remind us (ESA, 2019a). Unfortunately, due to the current situation, the ESA has completely cancelled the ExoMars mission (Science.lu, 2022).

Other countries are also developing missions to Mars:

• India’s Mars Orbiter Mission, arrived in orbit in 2016,
• The United Arab Emirates’ Hope Probe mission, sent to Mars in 2020,
• China’s Tianwen-1 mission, arrived in orbit and on Mars in 2021,
• Japan’s Mars Moons Exploration Mission, planned for 2024.

Finally, we note that this summary gives the impression that Mars exploration consists solely of successful missions. In reality, several missions have failed. A summary of all of the missions is available on Space.com (n.d.). This provides a good illustration of how scientific research works: History often only remembers the successes, whereas every discovery, invention or scientific breakthrough is and always will be preceded by several failures, which are not mentioned and are forgotten afterwards.

Of course, the discovery of the universe and the challenge of going further have always interested humans. The purely scientific reasons for exploring Mars are as follows:

• the search for life on Mars,
• characterisation of the climate and the geology of the red planet,
• preparation of the terrain with a view to future human exploration.

Understanding whether there is life outside Earth is a fundamental question. Since Mars is the planet most similar to our own, it is a favourite place to investigate this question.

Understanding the geology of Mars is important for understanding the planet’s history. Studying the atmosphere on Mars can help to understand the evolution of this atmosphere and why Mars currently has much less atmosphere than Earth. In the long term, these studies will help us to understand our Earth and the other planets in the solar system better.

Finally, one of the ultimate goals is human exploration. To pave the way, it is necessary to study the risks in advance. This is why robots are currently exploring and categorising the surface of Mars.

In the following video, Joel Levine, a planetary science expert, gives a great explanation of why missions to Mars are important from a scientific perspective.

The video is part of a series of eight talks on Mars (TED, n.d.).

The most exciting question of all of the missions to Mars is probably to discover whether there is life on Mars, in fossil form or even living.

One Martian day is close to the terrestrial 24 hours, and the planet has a similar inclination, so there are Martian seasons and even climatic regimes that correspond more or less to our own. There are lots of indications that Mars was once much more similar to our planet Earth. The photos and data that we have obtained from the various obiters and space probes that study Mars, indicate that even if Mars is a dry planet today, water once flowed on Mars. And where there’s water there’s life, because water is the main element required for life to develop.

The first probes, Viking 1 and Viking 2, which touched down on Mars in the 1970s, didn’t find life on Mars. This is not proof that there is no life. On the contrary, the microbes that NASA found at the bottom of frozen lakes in Antarctica give us hope of finding life on Mars, because the Antarctic climate resembles that of Mars today. On Earth, microbes were found in sedimentary rocks over 1,000 metres below the ground, but also in salt deposits and deep-sea chimneys (Alonso & Szostak, 2019). These findings indicate that our robots may not yet have looked in the right places on Mars.

The Viking mission had actually done four different experiments to see if there were bacteria in the Martian ground. At the time, the results of the four experiments seemed to eliminate the possibility of the presence of life. But today, almost 40 years later, scientists are able to explain the failure of the Viking experiments and the quest for Martian life remains open.

Today, scientists have also developed much more sophisticated and discrete techniques for detecting the presence of current or past life. The most well-known is based on the detection and sequencing of DNA. Nonetheless, this method is still problematic: even if DNA is common to all terrestrial life, it is not certain that extra-terrestrial life has a DNA. Research that is even more meticulous therefore focuses on different types of proteins and amino acids to search for extraterrestrial life forms (McKay & Parro García, 2014).

NASA’s rover Curiosity, and the future rover Rosalind Franklin are fitted with measuring instruments that make it possible to perform experiments based on these new technologies to search for traces of past or present life. The choice of landing spot for the rovers is one strategic aspect.

Finally, the detection of a biosignature gas in the atmosphere of planets and exoplanets is another method of searching for life. This is one of the missions of the new James Webb Space Telescope (Wolchover, 2021).

The Fermi Paradox: Where are they?

The question of the existence of life in the universe and outside our Earth is called the Fermi Paradox. In 1950, the physician Enrico Fermi (1938 Nobel Prize) is having lunch with his colleagues in Los Alamos. They are discussing a cartoon on extra-terrestrials which appeared in the New Yorker, when suddenly Fermi says: “Where are they?”. His colleagues instantly understand that Fermi is referring to the fact that the sun is a relatively young star in our galaxy. Consequently, civilisations more advanced than our own should have appeared in the older planetary systems and have therefore colonised our galaxy in one way or another and thus have shown themselves to us. Please note, however that Fermi probably did not doubt the existence of other civilisations. The more likely explanations for the paradox are that interstellar travel is simply not possible, that the trip was not worth the effort, or that civilisations do not survive long enough to develop the necessary technologies (Gray, 2015).

We have seen in the previous paragraphs that one of the problems in the search for extra-terrestrial life is the fact that we don’t know exactly what life outside our planet might look like. This question is only the start of a much deeper question: what is life? This rather philosophical question seems simple, but it is actually far from having a clear answer, even from a purely scientific point of view.

First of all, it seems easy to decide whether something is living or not. Unfortunately, the world is full of borderline examples. Therefore, some things are alive according to one definition, whereas they are not according to another definition. In everyday life, this doesn’t pose a major problem. However, it’s catastrophic in the field of science, as the microbiologist Radu Popa from NASA explains: “This is intolerable for any science […] But a science in which the most important object has no definition? That’s absolutely unacceptable. How are we going to discuss it if you believe that the definition of life has something to do with DNA, and I think it has something to do with dynamic systems? […] We cannot find life on Mars because we cannot agree what life represents.” (Zimmer, 2021).

Finding a definition of life that satisfies everyone is proving very complicated. But that is what the molecular biologist Edward Trifonov tried to do in 2011. He examined 123 current definitions of life and tried to find a common sub-definition among them. The final result was that life is an “auto-reproduction with variation”. However, this definition was quickly dismissed: a computer virus reproduces with variation, but no one would say it is alive.

Then the philosophers have tried to find an answer by adopting different perspectives. One philosophical trend follows the principal of operationalism, according to which it is not absolutely necessary to find a universal definition for life. Each area of scientific research works with the definition best suited to it. Therefore the definition that NASA uses to look for life outside our planet differs from the one that doctors use to distinguish between alive and dead. But this doesn’t matter, the important thing is that the definition works for its own field of research.

Another trend goes more in the direction of family resemblance, which is a philosophical idea according to which we classify objects into different groups. The objects in the same group can be linked by their similarities without necessarily all sharing a common similarity. For example, to illustrate this idea: if we asked one person to give a definition of the word “game”, they would probably not be able to do it. A game can be played with two people, more or even alone. A game can have a winner and a loser, but it doesn’t’ necessarily have to fulfil this criterion. A game can be for children, but there are also games for adults. To find a clear, succinct definition for the term “game” is evidently not simple. However, if we were asked to identify, among different objects, which of them are games, we would probably have no difficulty in doing so. Intuitively, we know how to recognise a game, without having an exact definition. A game satisfies a certain number of criteria within a list of criteria, but without necessarily having to satisfy all of these criteria. And what if it was the same with the term “life”? In (Abbott & Persson, 2021), some researchers from the University of Lund have classified a long list of things into various categories, hoping to find the category that defines life. They have tried to establish a list of properties that are associated with life, without each living object necessarily having to satisfy all of these criteria. Unfortunately, this approach also poses a problem. One of the properties of living things was order (living things have coordinated and organised structures), as do snowflakes (which we cannot class in the living things category). Another property was that of DNA. However, red blood cells do not have DNA, whereas we would like to class them in the category of living things.

One category of organisms has really changed the perspective on what life is: extremophiles. These are organisms whose normal life conditions are fatal for most other organisms. The tardigrade is one well-known example.

The tardigrade, the cutest of all the extremophiles

The tardigrade, also known as the water bear, is an organism of half a millimetre long (just big enough to be seen by the naked eye) which lives almost everywhere on the planet. It can be found in salty or fresh water, as well as in humid terrestrial environments such as forest mosses. The tardigrade is often referred to as the champion of extremes because it can survive in the most hostile of environments: it can withstand temperatures of -272°C to 150°C and up to 6,000 bars of pressure. It can also be exposed to ultraviolet rays and X-rays. It can go without food or water and put itself in a state of stasis for over 10 years. Once its state of stasis has finished, it can reactivate its metabolism.

In 2007, during the TARDIS experiment (Tardigrades in Space), ESA researchers sent 3,000 tardigrades on a 12-day space mission. “Our principal finding is that the space vacuum, which entails extreme dehydration and cosmic radiation, was not a problem for water bears,” the head of the TARDIS project explained (ESA, 2008).

Recently, the ESA kept tardigrades outside the international space station (ISS) for even longer and they survived the space vacuum, extreme temperatures and solar rays. Previously, scientists were convinced that these conditions were incompatible with any life form (ESA, n.d.a).

We also invite you to check out ESERO Luxembourg’s Space Bears activity.

Carole Cleland, philosopher at the University of Colorado, suggests an even more radical approach. For years, she has observed, collaborated and discussed with several researchers in different areas and from different institutions (in particular NASA). And the thing they all have in common is that their research is concerned with life. She drew a series of scientific articles from this, which have been collated into a book (Cleland, 2019). Her conclusion: scientists should simply stop looking for a definition of life, because it is one of those undefinable concepts. After all, according to Cleland, “we don’t want to know what the word ‘life’ means to us, we want to know what life is”.

For a complete overview of the scientific and philosophical discussions around life, we refer the reader to (Zimmer, 2021) or (Zimmer 2021a).

Sending robots to Mars offers many advantages. Firstly, it is much easier to ensure a robot’s safety than a human’s. When humans didn’t know any better, they sent animals like dogs or monkeys on space missions to find out what a human needed. Today, we know that it can be very dangerous for humans to go further into space than the ISS (International Space Station). What’s more, robotised missions are always less expensive than missions with humans (even if they are clearly less spectacular). From an organisational perspective, robots are less vulnerable than humans and can operate in much more hostile environments. Lastly, there are several tasks that a robot can accomplish better than a human.

However, as we have seen in this module, these robots cannot be programmed from Earth, because a signal coming from Earth would take too long (around 20 minutes) to travel from Earth to Mars. These robots therefore have to be programmed in advance and then function autonomously.

On Mars, the robots collect a lot of information that they have to send to Earth. This represents quite a large flow of data which can’t currently be processed in space and has to be sent in the form of raw data. Furthermore, Martian rovers don’t have all the laboratories that we have here on Earth. Outside the ISS, we can currently only use computers in space that are about as powerful as the ones we had on Earth 20 years ago. “Without the protection of the Earth’s magnetic field or the ISS shield,” explains Professor Marcus Völp, researcher at SnT (Interdisciplinary Centre for Security, Reliability and Trust) at the University of Luxembourg, “the computers we use on Earth would make a lot of mistakes and would end up getting fried because of the radiation in space. However, we do need calculating power by the time we want to collect the first matter from asteroids using swarms of robots.” This is why research is investing in the development of “supercomputers” which will be capable of working in space and processing raw data directly on location, so that only useful data is sent back.

Of course, we must make the robots and supercomputers secure with regard to sources of natural errors” continues Professor Völp, “but we must also protect them from sabotage. The best way to achieve this is to allow the robot to make mistakes, just like pupils do at school sometimes, without anything terrible happening (for example by allowing pupils to help other pupils and other robots to help other robots).”

The ISS is already welcoming astronauts who will soon be near the Moon and one day on Mars. However, we can’t train all astronauts in IT: these supercomputers will therefore have to be as autonomous as possible. That’s where artificial intelligence comes into play.

Artificial intelligence will also play an increasingly important role in the robots. The European Space Agency (ESA) and the National Aeronautics and Space Administration (NASA) are planning to send a rover to Mars in 2026. Its mission will be to collect tubes containing samples of Martian ground. These tubes will have been placed on the ground previously by the rover Perseverance (see above). The new rover will be called Fetch (from the verb to fetch). It must be capable of moving around as autonomously as possible, to find the tubes and retrieve them. To do this, the rover Fetch will use artificial intelligence and image-recognition techniques so that it can find the tubes left on the ground autonomously (ESA, 2020).

The University of Luxembourg and the SnT are conducting research in all of these areas: error tolerance, artificial intelligence on robots and many others.

Training Videos

These videos can also be used as an introduction to the teaching unit.

Paxi – The Red Planet

Paxi – Do Martians exist?

Exomars – A promising future

Referenzen
Abbott, Jessica K. & Persson, Eric. (2021). The problem of defining life: a case study using family resemblance. [Preprint]
Alonso, Ricardo. & Szostak, Jack W. (2019). The Origin of Life on Earth. Scientific American, September 2019
Cleland, Carol. (2019). The Quest for a Universal Theory of Life: Searching for Life As We Don’t Know It. Cambridge Astrobiology (11). Cambridge: Cambridge University Press.
European Space Agency, ESA. (2008). Tiny animals survive exposure to space. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Research/Tiny_animals_survive_exposure_to_space
European Space Agency, ESA. (2019). Missions to Mars. https://www.esa.int/ESA_Multimedia/Images/2019/05/Missions_to_Mars
European Space Agency, ESA. (2019a). ESA’s Mars rover has a name: Rosalind Franklin. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/ExoMars/ESA_s_Mars_rover_has_a_name_Rosalind_Franklin]
Euorpean Space Agency, ESA. (2020). Sample Fetch Rover for Mars Sample Return campaign. https://www.esa.int/ESA_Multimedia/Videos/2020/02/Sample_Fetch_Rover_for_Mars_Sample_Return_campaign
European Space Agency, ESA. (n.d.). Exploring Mars. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Exploration/Mars
European Space Agency, ESA. (n.d.a). Exposure to space and Mars. https://www.esa.int/Science_Exploration/Human_and_Robotic_Exploration/Blue_dot/Exposure_to_space_and_Mars
Gray, Robert H. (2015). The fermi paradox is neither Fermi’s nor a paradox. Astrobiology, 2015 Mar;15(3):195-9.
McKay, Christopher P. &  Parro García, Victor. (2014). Thow to Search for Life on Mars. Scientific American, June 2014
Science.lu. (2022). ESA stoppt gemeinsame Mars-Mission mit Russland. https://science.lu/de/esa-stoppt-gemeinsame-mars-mission-mit-russland
Space.com (n.d.). Mars missions: A brief history. https://www.space.com/13558-historic-mars-missions.html
TED (n.d.). What’s the big deal about Mars. https://www.ted.com/playlists/414/what_s_the_big_deal_about_mars
Wolchover, Natalie. (2021). The Webb Space Telescope Will Rewrite Cosmic History. If it Works. Quantamagazine. https://www.quantamagazine.org/why-nasas-james-webb-space-telescope-matters-so-much-20211203/
Zimmer, Carl. (2021). What is Life ? The Vast Diversity defies easy Definition. Quantamagazine. https://www.quantamagazine.org/what-is-life-its-vast-diversity-defies-easy-definition-20210309/
Zimmer, Carl. (2021a). Life’s Edge. The Search for what it means to be alive. New York, NY : Dutton.