One home

The recent technological triumph of the Perseverance rover and the Ingenuity helicopter have put Mars back on the front burner of the mass public mind.  Elon Musk's "Space-X" (the X seems to be short for "exploding") rockets have also been in the news, reminding us of the fascination of certain addled billionaires with the idea of sending humans to Mars or even colonizing it.  I've addressed this idea before (see here too), but it's worth another look.

To begin with, of course, there's the issue of cost.  NASA estimates that even a short manned expedition to Mars, equivalent to the Apollo 11 expedition to the Moon, would cost $450 billion (yes, with a "b").  The cost of a permanent settlement for a population large enough to be permanently viable -- at least a few hundred people -- would certainly be in the trillions.  I can’t imagine any government diverting such resources to a project with such meager rewards and dubious chances for success, nor any democracy's taxpayers tolerating such waste.

This cost issue is why natural resources on other planets are irrelevant to space travel.  Even if the surface of Mars were littered with cut diamonds and bars of refined gold and platinum, their market value would not cover the cost of bringing them back to Earth.  Not even close.  Some people are befuddled by a perceived analogy between modern space travel and the European age of exploration which led to colonizing and exploiting other continents. It's an analogy every aspect of which is totally inapplicable in reality.  Not only the costs but the distances and environmental differences involved are vastly greater.

Even if some future technological breakthrough makes space travel cheaper, the fact that Mars's gravity is only one-third as strong as Earth's is probably fatal to the entire concept of colonizing the planet.  All humans, all the apes from which we are descended, all the monkeys from which those apes were descended, and so on back to the first lobefin fish that emerged from the ocean hundreds of millions of years ago -- every one of them lived every moment of its life in Earth's gravitational field.  Given what we've seen of the physical damage caused to the human body by a few months at zero gravity on the Space Station, it's hard to imagine that an entire lifetime spent at one-third Earth-normal gravity wouldn't do serious harm.  Various schemes have been proposed for modifying Mars's atmosphere and temperature, but we will never be able to change its gravity.

Nor is it plausible that we will ever be able to change the planet's magnetic field, which is far weaker than Earth's.  Our homeworld's magnetic field deflects most of the dangerous radiation that pervades interplanetary space, but the surface of Mars is utterly exposed to such radiation, and even an Earthlike atmosphere would do little to alleviate this problem.  Earthly life, whether humans, animals, or plants, would suffer serious damage simply from being outdoors for long periods of time, unless it had burdensome protection which is unnecessary under Earth's protective magnetic canopy.

Mars is closer to the asteroid belt than Earth is.  It's been estimated that an asteroid impact equivalent to a one-megaton H-bomb happens somewhere on Mars once every three years.

In every place where we’ve tested it, the soil on Mars is saturated with chemicals called perchlorates which are known to be lethally poisonous to Earthly soil bacteria.  All Earthly plants depend on soil bacteria to mediate their assimilation of nutrients from the soil.  Before we could grow any kind of Earthly plants on Mars, even if we somehow made the atmosphere perfectly Earthlike, even if the low gravity wasn't harmful to Earthly plant biology, we would need to introduce Earthly bacteria -- but the chemistry of the Martian soil would kill them.

So we will never be able to grow crops on Mars, or grow trees or flowers.  There can never be Martian wheatfields or forests. I suppose a colony could sustain itself with hydroponics, but people there could never escape the awareness that they were living in an artificial, encapsulated environment surrounded by a poisonous desert where they didn’t belong.

It is sometimes objected that humans are highly adaptable, as shown by the diverse environments we've colonized on Earth.  Yet this adaptability has limits.  There are some fairly large areas of land on Earth which have never been inhabited by humans because conditions are too harsh.  Aside from Antarctica, there’s the Empty Quarter in eastern Arabia, a huge chunk of the interior of Australia, and some areas around the Arctic.  All those places have Earth-normal gravity and breathable air, and there have been humans living nearby for thousands of years who would not need advanced technology or huge amounts of money to get there.  Yet those places have never been settled with permanent human populations because the environments are too hostile.

Even if the enthusiasts of this absurdity someday manage to con some government into investing the trillions necessary to realize their dream, the result will never be more than a domed-over encampment of a few hundred people wracked with constant health problems from the low gravity, unable ever to step outside without elaborate protection, dependent on advanced technology to produce food and usable water and probably even air, always aware of the tens of millions of miles separating them from all the rest of humanity.  The covid-19 pandemic has shown us how tormented most people feel by a few months of "lockdown" at home.  Just imagine the effects of an entire lifetime under Mars's far more alien and isolated conditions.

I suspect that subsequent generations, rather than "adapting" to this sterile alien prison, would gaze with longing at the blue morning star in their sky, where they knew people could walk on grass among the trees and eat the natural fruit of the land.  Within a century the colony would be abandoned, humans returning to the true home of their kind.

Beyond Earth, the solar system consists of a few spheres of uninhabitable wasteland and poisonous chemicals separated by inconceivably huge expanses of absolutely nothing.  Our present approach -- exploring it with robots -- is the correct one.  Sending humans out there would be too expensive, too dangerous, and pointless.

We evolved on Earth and we are adapted to Earth.  A toxic irradiated frozen desert with meager gravity and almost no air is never going to be another Plymouth Rock.  This idea is a delusion.  So long as humans remain a biological species, there is only one planet we can call home.