Colonizing Mars Means Contaminating Mars — And Never Knowing For Sure If It Had Its Own Native Life

Since the start of the space age, scientists have taken the threat of biological contamination of other worlds seriously. As early as 1959, NASA held meetings to debate the necessity of sterilizing spacecraft that might be sent to other worlds. Since then, all planetary exploration missions have adhered to sterilization standards that balance their scientific goals with limitations of not damaging sensitive equipment, which could potentially lead to mission failures. Today, NASA protocols exist for the protection of all solar system bodies, including Mars.

NASA’s Galileo mission explored Jupiter and its moons from 1995 until 2003. Given Galileo’s orbit, the possibility existed that the spacecraft, once out of rocket propellant and subject to the whims of gravitational tugs from Jupiter and its many moons, could someday crash into and thereby contaminate Europa.

Such a collision might not occur until many millions of years from now. Nevertheless, though the risk was small, it was also real. NASA paid close attention to guidance from the National Academies’ Committee on Planetary and Lunar Exploration, which noted serious national and international objections to the possible accidental disposal of the Galileo spacecraft on Europa.

To completely eliminate any such risk, on Sept. 21, 2003, NASA used the last bit of fuel on the spacecraft to send it plunging into Jupiter’s atmosphere. At a speed of 30 miles per second, Galileo vaporized within seconds.

Mars is the target of seven active missions, including two rovers, Opportunityand Curiosity. In addition, on Nov. 26 NASA’s InSight mission is scheduled to land on Mars, where it will make measurements of Mars’ interior structure. Next, with planned 2020 launches, both ESA’s ExoMars rover and NASA’s Mars 2020 rover are designed to search for evidence of life on Mars.

The Curiosity rover was tested under clean conditions on Earth before launch to prevent microbial stowaways.

Credit: NASA/JPL-Caltech, CC BY

The good news is that robotic rovers pose little risk of contamination to Mars, since all spacecraft designed to land on Mars are subject to strict sterilization procedures before launch. This has been the case since NASA imposed “rigorous sterilization procedures” for the Viking Lander Capsules in the 1970s, since they would directly contact the Martian surface. These rovers likely have an extremely low number of microbial stowaways.

But when Earth sends astronauts to Mars, they’ll travel with life support and energy supply systems, habitats, 3D printers, food and tools. None of these materials can be sterilized in the same ways systems associated with robotic spacecraft can. Human colonists will produce waste, try to grow food and use machines to extract water from the ground and atmosphere. Simply by living on Mars, human colonists will contaminate Mars.

Some scientists believe they have already uncovered strong evidence for life on Mars, both past and present. If life already exists on Mars, then Mars, for now at least, belongs to the Martians. Mars is their planet, and Martian life would be threatened by a human presence there.

Does humanity have an inalienable right to colonize Mars simply because we will soon be able to do so? We have the technology to use robots to determine whether Mars is inhabited. Do ethics demand that we use those tools to answer definitively whether Mars is inhabited or sterile before we put human footprints on the Martian surface?

David Weintraub, Professor of Astronomy, Vanderbilt University


This article is republished from The Conversation under a Creative Commons license. Read the original article. Follow all of the Expert Voices issues and debates — and become part of the discussion — on FacebookTwitter and Google +. The views expressed are those of the author and do not necessarily reflect the views of the publisher. This version of the article was originally published on


This article was originally published at The Conversation. The publication contributed the article to’s Expert Voices: Op-Ed & Insights.

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