Shall we settle on Mars?

Microbes on marsIs there something alive?

The time has come on February 18th. It's rover time on Mars again. A huge heat shield. A supersonic parachute the size of a family home. And at the end a "Sky Crane". The floating platform automatically lowers a vehicle on a rope. "Perseverance" lands near an ancient river bed. Here the rover will take samples and pack them for transport back to earth. Assuming we find traces of life in it: Are these really extraterrestrials?

The earth has everything that life needs. Oceans, fertile land, an atmosphere of oxygen. The blue planet was first shaped by microbes, and later by plants and animals. But where did life come from?

Knowledge gap at the origin of life

The theory says: At some point, four billion years ago, on the storm-swept, inanimate earth contaminated by volcanic eruptions, it happened: maybe in a puddle, maybe also in the porous rock of a hot deep-sea spring. Nobody really knows. Nor does Fred Goesmann, a researcher at the Max Planck Institute for Solar System Research in Göttingen.

"It is actually epistemologically appalling how stupid we are with regard to life compared to the rest of the world. So as far as physics and chemistry are concerned, we are a lot further. We know the universe. But we are with regard to life we are still really beautiful on our lonely little island. "

Astronauts Buzz Aldrin and Neil Armstrong hoist the US flag on the lunar surface during the Apollo 11 mission (imago images / UPI Photo)

First excursion with microbe risk - the moon landing

"Houston, the eagle has landed." In July 1969 mankind set out to leave this island for the first time. Neil Armstrong and Buzz Aldrin raise a flag. They drill into the rock, collect moondust and load everything into their space capsule before they get in and take off their spacesuits. Moondust turns their faces soot-black, and their hands are full of it too.

At this point in time, nobody knows whether the dust contains lunar bacteria or disease-causing viruses. Germs from space should be prevented from reaching earth at all costs. A laboratory has been built in Houston in a rush to record lunar samples and the astronauts. The building resembles an S4 laboratory for biological weapons, with several locks and the highest level of security. For the astrobiologist Andrew Schuerger from the University of Florida, this caution was also appropriate from the point of view of the time.

"We had no information on whether life could survive in interplanetary space. The quarantine for the Apollo astronauts was probably intended as an additional level of security."

But the possibly contaminated astronauts have to come to Houston first. The mobile quarantine unit is a hermetically sealed stainless steel container, equipped with a dining room, bunk and a kitchen. All in all, three weeks of strict quarantine are planned.

Absolutely not a good idea in terms of the risk of contamination - the Apollo 11 landing capsule is already being opened on the water (NASA)

The hygiene concept was a disaster

The first flight of humans to the moon and back is a historic success - but its hygiene concept is a disaster. The lunar pilots, who have just landed in the Pacific, are not heaved onto the deck of the aircraft carrier in their still-closed capsule as planned. The hatch is opened by divers while the capsule is still floating in the Pacific. If there had been deadly moon germs in the capsule - now they would have escaped into the warm, humid Pacific air.

The astronauts reach the mobile quarantine unit in protective suits. A few hours after the beginning of their isolation, they answer questions from US President Richard Nixon, who is himself on the aircraft carrier - he speaks to them through a pane of glass: "Neil, Buzz and Mike, you should know that I am the happiest man on the world am. "

What nobody on board knows is what Buzz Aldrin will later refer to as the Waterloo moment for NASA technicians. Ants come and go in the tiny kitchen soon after they are transported to the mainland. The mobile quarantine unit was not completely closed. The fact that the moon travelers did not introduce any deadly germs is due to a fortunate circumstance: the moon is uninhabited. Andrew Schuerger:

"The sun is not weakened on the moon because there is no atmosphere. The outermost layer of the moon's surface can get 140 degrees Celsius when the sun is at its highest. At this temperature, bacteria sterilize within a few hours."

View from the "Viking" space probe onto the Martian soil (picture-alliance / dpa)

The moon is "dead" - but Mars?

Everything we know today about the beginning of life are fragments. Ancient rocks on earth, which might have provided answers, have long since destroyed wind, weather and the constant movements of plate tectonics. The moon cannot add anything to the question of life. But on Mars it looks very different. 60 years ago, the planet moved within the reach of space travel. It is measured from orbit. Then in 1976 NASA landers hit the surface for the first time with Viking 1 and Viking 2. Scientists almost expect to find life. If not higher plants and animals, at least tiny bacteria or fungi. Fred Goesmann:

"I would also deny that the people who built Viking were naive. So from their level of knowledge, they made fantastic instruments, really."

Three of the experiments immediately give negative results. The fourth soaks the Martian dust with a nutrient solution labeled with radioactive carbon-14. In fact, it only looks as if microbes in the Martian dust have digested the nutrients. Another interpretation appears much more likely later:

"Then there were nasties that were only discovered decades later. Damn it, there are perchlorates." A salt in the Martian dust that sizzles and decomposes the nutrient solution. "Yes, great, you really didn't know that beforehand."

Search for microbes postponed for now

After Viking, NASA stopped looking for microbes for the time being. Spirit and Opportunity, two rovers that will roam dry and cold Martian plains from 2004, are only supposed to examine habitability. Quite similar to the target of Curiosity, the rover that will be deposited in a huge crater in 2012 with a parachute and a sky crane. The results are unanimous: yes, there were streams and lakes four billion years ago. But whether something is still alive in the sediment today: none of the rovers tried to find out. Why not?

"I use the word cautiously. We have a responsibility for our own lives. The first contact only happens once. It's like the first date, you can't do it a second time. And I think we have to think it through very carefully." . Perhaps we have even carried problematic terrestrial organisms to Mars because we cannot launch a probe that is completely sterile. "

Planetary Protection Guidelines

Lisa Pratt recently told Planetary Radio podcast about a maxim NASA has been following since the lunar program. Pratt is also an astrobiologist - at NASA she is responsible for planetary protection. Her counterpart at ESA is Gerhard Kminek: "The Planetary Protection guidelines, which are ultimately based on the United Nations Space Treaty, are not environmental guidelines."

However, it is more than just a declaration of intent. The space treaty is legally binding, ratified by 110 states. So it's almost law. The only law that applies to the moon, Mars and all other celestial bodies outside the earth. And it has two simple principles.

Number 1: Nobody should release germs from another celestial body on earth.

And principle number 2: Nobody should bring earthly germs to another celestial body if that could later impair the search for life.

In retrospect, both principles were fulfilled on the moon. Because he was dead and should remain so in the future. It looks very different on Mars.

"Landslide" on Mars - the surface is very unstable in many "special areas" (

Conditions on Mars call for caution

More than ever, researchers believe that the conditions on our neighboring planet are compatible with life. Andrew Schuerger:

"Because of its thin atmosphere. The likelihood of contaminating it is simply much greater because everything is being dispersed by the globally circulating winds. And then there are places on Mars where hydrated water is fairly certain to be found."

All of this makes Mars interesting for the search for extraterrestrial life. And at the same time it forces you to be extremely careful before entering the country. Andrew Schuerger is investigating the survivability of space probes mounted on Earth on behalf of NASA. Christine Moissl-Eichinger from the Medical University of Graz does this for the European Mars probes: "Before you enter the clean room, you have to change your clothes. That goes right down to your underwear."

Space probes leaving for the Red Planet today go through a meticulous procedure. Some are screwed together in a tent that is in a clean room. A clean room in a clean room. Gerhard Kminek:

"If I have a particle, I have a particle. It's there today, and if I don't do anything about it, it will be there tomorrow and the day after and in two weeks. If I have biological contamination, a particle can become more . "

Precautions are costly

Space probes are no longer completely baked to sterility as in the early days of space travel - because their electronics would be damaged. Moissl-Eichinger: "So I have to think about every single device, every single component: I make it sterile beforehand, how it works. I can either treat the parts with alcohol or irradiate them or with all different methods and then build it that way clean as possible together. "

Gerhard Kminek: "The costs for a typical Mars mission, which are also caused by the planetary protection rules, are in the range of a small instrument."

Fred Goesmann: "I think samples are taken every few days to see if something is growing or germinating. It's a crazy effort."

The irony of Mars research: The closer the rover is to possible biotopes on Mars, the more complex and expensive the procedure on Earth will be. And sometimes even the best disinfection is not enough.

"Special Regions" on Mars

"So these special regions, this concept." Special regions, a favorite topic for Planetary Protection Officer Gerhard Kminek. "This concept was established when it was discovered a few years ago that there are areas on Mars where there is evidence that modern water is still active."

It is about regions on the surface of Mars that change again and again within a few years. On mountain edges, volcanoes and on crater slopes. Dark welts form that seem to come out of nowhere. A whole section of the slope is suddenly discolored. Why?

The pressure of the Martian atmosphere is just one thousandth of the earth's air pressure and the temperature is almost always below freezing point. The most important condition for life, bubbling, liquid water, is not fulfilled on the surface. But on the darkly discolored slopes, salt could act like an antifreeze - and keep water liquid. That is why it is now strictly forbidden to land space probes there.

"This is essential when selecting the landing area for each probe, because there is always the chance that the landing will not succeed."

Self-portrait of the Mars rover "Curiosity" (Getty Images NASA / JPL-Caltech / MSSS)

Would earth microbes survive in the Martian dust?

In 2015, such a dark landslide zone appeared near the NASA rover Curiosity. Actually, an ideal opportunity to check out what is arguably the most promising habitat for life on Mars. But that didn't happen: NASA's Planetary Protection unceremoniously forbade the mission team to drive into the zone. Because it could not be ruled out that there weren't any earth microbes on Curiosity after all. Dirk Schulze-Makuch from TU Berlin:

"The fear is that these places could be contaminated with microbes from the earth. And that it would be really difficult with a mission afterwards. At least if this mission brings the appropriate instruments to be able to say that it is indigenous Life on Mars. "

The American-German astrobiologist does not see it quite as critical. Of course, it cannot be ruled out that Curiosity still carries some earth microbes with it. Since the rover has no instruments to detect life, it has never been sterilized as thoroughly as the Viking probes. But why should these germs be able to prevail in Martian dust, of all places?

"I think there is always a bit of earth arrogance in there, because we believe that the earth organisms are better adapted than any indigenous Martian organisms. If there were Mars organisms there, they would be much better adapted. It is just as if we were, for example, monkeys to Antarctica and are afraid that they will drive away penguins. The penguins are much better adapted there. And the Martian organisms would also be much better adapted than any earth organisms that come there. "

Much is being done in the search for extraterrestrial life without actually making any headway. That bothers Schulze-Makuch. He says: If we want to prove that there is life, we should finally go to where it is most likely.

How realistic Elon Musk's plans for colonizing Mars are remains to be seen (picture-alliance / dpa)

Elon Musk's plans could revolutionize anything

In addition, a few earth microbes on board old Mars rovers could soon be the slightest problem.

"How do we get you to Mars? How do we build a self-sustaining city there that is more than an outpost - so that Mars becomes a planet in its own right and we become a true multi-planetary species?"

Elon Musk, head of the rocket builder SpaceX 2016 at the International Astronautical Congress in Guadalajara, Mexico. Musk wears a white shirt with no tie. He stutters, as is his way, and yet the audience hangs on his every word. On the screen behind him appears a picture of a person in front of a huge window. And behind the window the sun is just rising over the red planet.

SpaceX is currently making money launching satellites into orbit and capsules to the space station. But Elon Musk does not want to be satisfied with that. Humanity is to become a multi-planetary civilization in case something goes wrong on good old earth. SpaceX is working on the next big step.

The vision: settlers on Mars

It's a rocket that dwarfs the old Saturn V rocket. A spaceship for the transport of heavy loads and people far from Earth. Musk does not want to send individual researchers to Mars, as NASA plans to one day, but settlers. He wants to launch thousands of rockets within the next few decades and transport them to Mars with 200 passengers each.

The new plans pose an unsolved problem, or more precisely, a whole host of problems. There are 30 trillion microorganisms on the skin and in the intestines of every single person.

How can we believe we can still find native microbes on Mars when people are constantly on the move?

"Well, um." "Yes, of course you are right. We as humans have a lot of microbes." "This is difficult." "This is a huge topic." "If astronauts really live on Mars."

The ISS space station is mankind's most remote outpost - but not at all germ-free (dpa / NASA)

Microbes sample in the space laboratory

The microbiologist Christine Moissl-Eichinger had an experiment carried out on the International Space Station in 2017. Not in one of the many boxes that securely shield every experiment behind glass. Instead, astronaut Jack Fischer only has one thing to do: he should float through the space station. And clean. "It wasn't much cleaner afterwards than before, I think."

He wipes handrails, laptops, exercise equipment and the dining table with sterile cloths.

"We're used to it here on earth, if something smells strange, then the window is opened and we just ventilate well and everything is fine. That is of course a bit limited on the ISS."

The ISS is a special environment. The only one that is completely and permanently decoupled from Earth is apart from the occasional arriving crew and supply spaceships.

"The humidity is relatively high. We know that because the devices have to work and because static charges have to be prevented. And humidity is always good for microbial growth. And yet everything has to be under control, because infections could happen by themselves Germs are transferred from the surface to the mucous membranes. "

ISS is by no means free of germs

The cleaning cloths end up in the laboratory of the Graz microbiologist.The result is reassuring from the astronaut's point of view. No particularly harmful organisms. But the ISS is by no means free of germs.

"In humans, Corynebacterium sits on the skin or in the nose. Lactobacyllus, a typical vaginal germ, is also found in the oral cavity. We found a lot of Staphylococcus, a typical skin germ that each of us carries with us. Streptococcus. Acinetobacter, a microorganism that can survive on surfaces for an unbelievably long time. "

But what does all this mean for an environment on another planet - and for the search for life?

"You have to think about how to deal with it and how you cannot carry and control the contamination of humans everywhere. That is the most difficult thing: How do you control microbes that we give out in an uncontrolled manner?"

Similar to this Mars experiment, people on Mars would only be able to move in space suits (imago stock & people / Gil Cohen Magen)

Contamination initially slowed down by spacesuits

Gerhard Kminek believes that there will probably not be an immediate exodus of introduced microbes into the local environment on Mars. Microbes would initially be couch potatoes: "Of course we don't run around naked on Mars and throw our contaminants around there. We have our spacesuits that are very tight. If they weren't tight, we wouldn't survive."

ESA's planetary protection officer says: The United Nations is currently revising guidelines to prepare for the arrival of humans. And representatives of space companies are now also sitting there. So the problem is being worked on.

"Regardless of this, there is of course a much higher level of biological contamination that a crew would take to Mars than if we simply sent a machine."

The start of the ExoMars mission with the European-Russian rover "Rosalind Franklin" was postponed by two years due to the corona pandemic (Copyright ESA / ATG medialab)

Short time frame until the person arrives

There may be a time window of ten years in which to take a close look at Mars with space probes before humans arrive. The interest is lively: In February 2021, the first Chinese Mars probe Tianwen-1 and the orbiter Al Amal from the United Arab Emirates will enter orbit.

The star among the robotic newcomers is likely to be Perseverance. In the Jezero crater, the NASA rover is to collect samples in a dry river delta and pack them in 43 containers. Further space probes are to bring the containers back to earth for closer examination in a few years.

Before that, however, "Rosalind Franklin" will also arrive: a European rover named after the discoverer of the structure of the hereditary molecule DNA. As things stand, the arrival is planned for 2023. For the first time since the Viking, a lander will be able to track down life on the red planet. Fred Goesmann from the Max Planck Institute in Göttingen is responsible for the "Mars Organic Molecule Analyzer" on board. He hopes to find levorotatory amino acids. Fatty acids that we know from cell membranes. Anything indicative of living or extinct organisms. But he doesn't want to promise too much.

"We are very careful here and say: Biology will probably not be able to cope entirely without an organizing structure. Simply complete chaos is not enough. Therefore, the search for structures, for any irregularities, deviations from the statistical composition. That is not really that yet Proof of life, that's right. It's a little more careful. "

Proof of life becomes a tough circumstantial process

Evidence of life on Mars, if it exists, is likely to be a tough circumstantial process. There should be justified doubts about the first findings. Earlier there were sensational reports about fossilized Martian microbes that did not stand up to scientific assessment. In addition, the capabilities of each space probe are limited anyway. Goesmann:

"The really exciting thing will be this slow learning curve. If you have enough sample material, you can take a look at it first. And then decide which is the most appropriate tool for this kind of test. We don't have that with us on Mars. We have our tool kit with them, ready. For example, we can't do any wet chemistry. We can't cook any digestions. You could do that on Earth. "

What if it actually works and one day we discover life? It would probably be tiny microbes that hide several centimeters deep in the dust from harsh UV radiation. If these tiny things really exist, shouldn't we call off the settlement plans?

Cancel settlement plans in case of doubt?

"We must first do everything we can scientifically." Andrea Owe explored the ethics of human activity in the extraterrestrial environment at the University of Oslo. "We have to make sure we do it in an ethical, responsible way. Of course, some people say that if we find alien microbes, we shouldn't send people there. Others say it doesn't matter because it's just microbial life is. "

In the end, the discovery of life beyond the earth would be a scientific turning point, perhaps to be compared with the Copernican turning point in the 16th century, when man recognized that the sun was at the center of the planetary system. If we discover life elsewhere, it would once again straighten the earth - and raise countless new questions. Dirk Schulze-Makuch: "Is it life that is related to life on earth? Or is it life that has a separate origin?"

Christine Moiss-Eichinger: "Are we dealing with virus-like microbes, for example? Are we dealing with developed microorganisms that are specially adapted?"

A look at the genetic tree of life could reveal that terrestrial and Martian species are not only distant relatives, but that those on Mars are even older. Then life might have originated on Mars and only reached Earth later with a meteorite.

Future vision or nightmare? Martian settlers with their children born on the red planet (imago stock & people / Steven Hobbs / Stocktrek Images)

Backup of the terrestrial biosphere on Mars?

For Elon Musk, none of these considerations matter. He plans the colonization of Mars from the perspective of an Earthling who wants to break new ground. Andrea Owe:

"When it comes to our motives, it gets very interesting. If we say we don't just want a backup for humanity, but for the biosphere, that is, for the great history of life on earth, of which we are part, then that would be a pretty good reason for colonizing Mars. Of course, we don't know whether that is Elon Musk's motive. "

Where our microbial lodgers will settle when humans inhabit Mars remains to be seen. Some researchers predict that, like us, they would hardly survive outside of human habitats. Andrew Schuerger can also imagine a different scenario.

"We know places on Mars where there is permafrost, and that's only ten centimeters deep. If we started digging in there to get the water, and if we also kicked up microorganisms that we brought with us, which would then settle in you Distribute dust storms globally, then they could also end up in biological niches that we have not even explored. There is a great risk on Mars that contamination of a human colony or base will be distributed globally. "

Colonization is a basic biological principle

When humans colonize Mars, they will change it. We don't just bring our skin and intestinal flora with us. We should grow food. And some even want to transform the Red Planet, warm its climate so that terrestrial species can thrive on it in the long term. But can we do that at all? And who tells us that the Martian environment is also changing in our sense? Dirk Schulze-Makuch:

"Basically, from a biological point of view, colonization is everything that all animal species do, from ants to brown bears. And the organisms that don't are now extinct. We should keep that in mind."