Mars appeals because it is Earth-like in many ways. It rotates in just over 24 hours, so a day on Mars is almost identical to a day on Earth. Mars has a solid surface, a thin atmosphere and sunrises and sunsets. The rhythm of life on Mars would share the same rhythms of life as back home on Earth.
But readying Mars for life would be quite challenging. All terrestrial life requires water; Mars has water, albeit frozen at the polar caps, locked in permafrost or buried in aquifers deep underground. With effort, we probably could retrieve and then pipe that water to our Martian cities.
But Mars has a cold temperature (minus 80 degrees Fahrenheit). Initially, we could take blankets, solar panels and nuclear power generators with us. Then we would have to develop ways to warm up the atmosphere.
Even if we produced warmth and water, we would still need to oxygenate the atmosphere so that we could breathe. Mars currently has no free oxygen, but it has plenty of carbon dioxide that plants can use for photosynthesis and from which human engineers might extract breathable oxygen. Given enough time and ingenuity, one can imagine that we could solve this no-air-to-breathe problem. For the foreseeable future, Mars is at best a sanctuary for anaerobic life forms that can thrive at extremely cold temperatures.
Even with oxygen, living on a planet without an ozone layer to protect life on the surface from dangerous solar ultraviolet light and X-rays would be no fun. Furthermore, the thin atmosphere of Mars offers no protection from the high-speed particles known as cosmic rays that come from the sun and other stars in the Milky Way. Without a thick atmosphere and an ozone layer, the surface of Mars would be a terrific place if your goal is to develop radiation poisoning and cancer and then die.
Of course, scientists are working on solutions to these problems, too. We could start by living in caves or bunkers below the Martian surface. Or maybe we’ll figure out how to manufacture shelters made of special protective materials.
But, even with all that, we’re not quite ready for Mars.
Our most obvious problem is that, right now, a trip to Mars would be a one-way journey. SpaceX might be able to launch some potential colonists to Mars within a decade, and NASA soon thereafter, but with current rocket technology, neither SpaceX nor NASA can bring these spacefarers home. And the ethics of sending astronauts on a one-way journey to Mars are questionable.
Establishing a colony in a new, unknown world carries great risks. Those of us who send emissaries to another planet should make every effort to minimize those risks.
One major risk has been ignored: Mars may already be inhabited. As Carl Sagan noted when peering at Mars through the eyes of the Viking landers’ cameras in 1976, Mars has no macrobes — no bears, no rabbits, no mice, no wasps. Mars could, however, be host to an underground world of microbes.
Some scientists have interpreted their measurements of small levels of methane in the Martian atmosphere as evidence that Mars already is inhabited. This interpretation is by no means definitive, but it may be right. The best we can say, today, is that we do not yet know for sure that Martians exist; however, we also do not know for sure that Mars is sterile. The jury is still out.
Before we contaminate the red planet with our DNA, bacteria and viruses, we must establish whether Mars is biologically alive or dead. Pre-existing Martian life likely would have no defenses for the contamination we would insert into their world. And if Martian life exists and is related to terrestrial life through DNA or RNA molecules, we might have no defenses against the unintentional but inevitable contamination of Earth with Martian microbes.
That such elemental questions about the presence or absence of life itself on Mars have not yet been solved suggests that we do not know enough to consider living on Mars at this time.
Can we justify the risks to the lives of potential space travelers, when so many known problems related to surviving a trip to Mars remain unsolved and elemental questions unanswered?
SpaceX’s plans to send the first crewed flights to Mars in 2024 may be premature. And if Mars is already the home of Martians, they have squatter’s rights. Perhaps we should leave them alone.
David Weintraub, an astronomer and director of the Communication of Science & Technology program at Vanderbilt University, is the author of Life on Mars: What to Know Before We Go.He originally wrote this essay for Zocalo Public Square.