The closest place in the universe where extraterrestrial life might exist is Mars, and humans are ready to try to colonize the neighboring planet in the next decade. Before that happens, we need to realize that there is a very real possibility that the first human steps on the surface of Mars will cause collisions between terrestrial life and native Martian biota.
If the red planet is sterile, the presence of humans there will not create a moral or ethical dilemma in front of this. But if life is on Mars, human explorers can easily lead to extinction of Mars life. As an astronomer who explores these questions in my book "Life on Mars: What You Need to Know Before You Go," I argue that we, Earthlings, need to understand this scenario and debate the possible results of colonizing our neighboring planets . Maybe the mission that will bring humans to Mars requires a break.
Where life can be
Life, according to scientists, has several basic requirements. It can be anywhere in the universe that has liquid water, a source of heat and energy, and a large number of important elements, such as carbon, hydrogen, oxygen, nitrogen, and potassium.
Mars qualifies, as does at least two other places in our solar system. Both Europa, one of Jupiter's large moons, and Enceladus, one of Saturn's large moons, appear to have a prerequisite for hosting native biology.
I suggest that how scientists plan this two-month exploration mission provides a valuable background when considering how to explore Mars without the risk of contamination.
Under the layers of their thick ice, both Europa and Enceladus have global oceans where 4.5 billion years of stirring primordial soup may have enabled life to develop and take root. The NASA spacecraft has even portrayed a spectacular geyser that spouted clumps of water into space from this subsurface ocean.
To find out if the moon has life, planetary scientists are actively developing the Clipper Europa mission for the launch of the 2020s. They also hope to plan a future mission that will target Enceladus.
Be careful not to get contaminated
Since the beginning of the space age, scientists have taken the threat of biological contamination from other worlds seriously. In early 1959, NASA held a meeting to debate the need to sterilize spacecraft that might be sent to other worlds. Since then, all planetary exploration missions have followed sterilization standards that balance their scientific goals with the limitations of non-destructive equipment, which could potentially lead to mission failure. Today, the NASA protocol is for the protection of all solar system bodies, including Mars.
Because avoiding biological contamination from Europa and Enceladus is a high priority requirement that is well understood from all missions to the Jovian and Saturn environments, their moons remain uncontaminated.
NASA's Galileo Mission explores Jupiter and its months from 1995 to 2003. With Galileo's orbit, it is possible that the spacecraft, once out of a rocket propellant and subject to Jupiter's gravitational pull and many moons, could someday crash and with thus polluting Europa.
Such collisions may not occur millions of years from now. However, even though the risk is small, it is also real. NASA is very concerned about the guidance of the National Academy Committee on Planet and Moon Exploration, which notes serious national and international objections to the possibility of accidental disposal of the Galileo spacecraft on Europa.
To completely eliminate such risks, on September 21, 2003, NASA used the last bit of fuel in the spacecraft to send it to Jupiter's atmosphere. With a speed of 30 miles per second, Galileo evaporates in seconds.
Fourteen years later, NASA repeated this month-protecting scenario. The Cassini mission orbits and studies Saturn and its months from 2004 to 2017. On September 15, 2017, when the fuel ran out, instructions from NASA operator Cassini deliberately dropped the spacecraft into Saturn's atmosphere, where it was destroyed.
But what about Mars?
Mars is the target of seven active missions, including two inventors, Opportunities and Curiosity. In addition, on November 26, the NASA Mission mission is scheduled to land on Mars, where it will make measurements of the interior structure of Mars. Furthermore, with the planned 2020 launch, both the rover of NASA's ExoMar ESA and Mars 2020 are designed to look for evidence of life on Mars.
The good news is that robotic explorers have little risk of contamination to Mars, because all spacecraft designed to land on Mars are subject to strict sterilization procedures before launch. This has happened since NASA imposed a "strict sterilization procedure" for the Viking Lander Capsules in the 1970s, because they would immediately contact the surface of Mars. This inventor might have a very low number of microbial stowaways.
Every land biota that manages to stay outside the inventors will experience a very difficult time surviving for half a year traveling from Earth to Mars. The vacuum of space combined with hard X-ray exposure, ultraviolet light and cosmic rays will almost certainly sterilize the outside of the spacecraft sent to Mars.
Any bacteria that sneaks into one of the inventors might arrive on Mars alive. But if anyone escapes, the thin atmosphere of Mars will not offer protection from high energy, sterilizing radiation from space. The bacteria will likely be killed immediately. Because of this harsh environment, life on Mars, if it currently exists, almost certainly has to hide under the surface of the planet. Because there are no explorers who explore caves or dig deep holes, we don't have the opportunity to deal directly with possible Mars microbes.
Given that Mars exploration has so far been limited to unmanned vehicles, the planet is likely to remain free of terrestrial contamination.
But when Earth sends astronauts to Mars, they will travel with life support and energy supply systems, habitats, 3D printers, food, and equipment. None of these materials can be sterilized in the same way as the systems associated with robotic spacecraft. Human colonies will produce waste, try to grow food and use machines to extract water from the soil and the atmosphere. Enough to live on Mars, human invaders will pollute Mars.
Cannot play back hours after contamination
Space researchers have developed a careful approach to the exploration of Mars robots and a hands-off attitude towards Europa and Enceladus. Then, why are we collectively willing to ignore the risks to human life Martian exploration and colonization of the red planet?
Contaminating Mars is not an unexpected consequence. A quarter of a century ago, a National Research Council report entitled "Biological Contamination of Mars: Problems and Recommendations" confirmed that the mission of bringing humans to Mars would surely pollute the planet.
I believe it is very important that every effort is made to get evidence of past life or now on Mars far before future missions to Mars that include humans. What we find can influence our collective decision whether to send colonists there at all.
Even if we ignore or don't care about the risks that humans will pose to Martian life, the problem of bringing Mars life back to Earth has serious social, legal and international implications that deserve to be discussed before it's too late. What risks might life Mars cause to our environment or our health? And does one country or group have the right to risk re-contamination if these Martian living creatures can attack DNA molecules and thus endanger all life on Earth?
But the second public player – NASA, United Arab Emirates Mars Mars 2117 project – and private – SpaceX, Mars One, Blue Origin – had planned to transport the colony to build a city on Mars. And this mission will pollute Mars.
Some scientists believe they have found strong evidence for life on Mars, both past and present. If life is already on Mars, then Mars, for now at least, belongs to a Martian. Mars is their planet, and Mars life will be threatened by the presence of humans there.
Does humanity have an irrevocable right to colonize Mars just because we will soon be able to do it? We have the technology to use robots to determine whether Mars is inhabited. Does ethics require us to use these tools to answer with certainty whether Mars is inhabited or sterile before we place traces of humans on the surface of Mars?
David Weintraub, Professor of Astronomy, Vanderbilt University
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