The closest place in the universe where extraterrestrial life might exist is Mars, and human beings are poised to attempt to colonize this planetary neighbor within the next decade. Before that happens, we need to recognize that a very real possibility exists that the first human steps on the Martian surface will lead to a collision between terrestrial life and biota native to Mars.
If the red planet is sterile, a human presence there would create no moral or ethical dilemmas on this front. But if life does exist on Mars, human explorers could easily lead to the extinction of Martian life. As an astronomer who explores these questions in my book “Life on Mars: What to Know Before We Go,” I contend that we Earthlings need to understand this scenario and debate the possible outcomes of colonizing our neighboring planet in advance. Maybe missions that would carry humans to Mars need a timeout.
Where life could be
Life, scientists suggest, has some basic requirements. It could exist anywhere in the universe that has liquid water, a source of heat and energy, and copious amounts of a few essential elements, such as carbon, hydrogen, oxygen, nitrogen and potassium.
Mars qualifies, as do 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 possess these prerequisites for hosting native biology.
I suggest that how scientists planned the exploratory missions to these two moons provides valuable background when considering how to explore Mars without risk of contamination.
NASA/JPL/Space Science Institute, CC BY
Below their thick layers of surface ice, both Europa and Enceladus have global oceans in which 4.5 billion years of churning of the primordial soup may have enabled life to develop and take root. NASA spacecraft have even imaged spectacular geysers ejecting plumes of water out into space from these subsurface oceans.
To find out if either moon has life, planetary scientists are actively developing the Europa Clipper mission for a 2020s launch. They also hope to plan future missions that will target Enceladus.
Taking care to not contaminate
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.
Since avoiding the biological contamination of Europa and Enceladus is an extremely well-understood, high-priority requirement of all missions to the Jovian and Saturnian environments, their moons remain uncontaminated.
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.
Fourteen years later, NASA repeated this protect-the-moon scenario. The Cassini mission orbited and studied Saturn and its moons from 2004 until 2017. On Sept. 15, 2017, when fuel had run low, on instructions from NASA Cassini’s operators deliberately plunged the spacecraft into Saturn’s atmosphere, where it disintegrated.
But what about Mars?
Mars is the target of seven active missions, including two rovers, Opportunity and 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.