A Tale of Two Marses, Part Two

The discovery of water on Mars has forced us to reevaluate everything we thought we knew about the Red Planet. Right now, scientists have to be cautious when talking about Mars. Too much remains unknown or uncertain.

But I’m no scientist. I’m a science fiction writer. Yesterday, I took you on an imaginative tour of one possible version of Mars: a Mars that managed to trap immense quantities of water deep underground, protecting it from the ravages of the solar wind.

Today, let’s visit a rather different kind of Mars.

MARS: AN ATMOSPHERIC WATER WORLD

Ancient Mars possessed a dense atmosphere of carbon dioxide and vast oceans of liquid water. This environment supported a fledgling ecosystem of anaerobic bacteria, much like that found on ancient Earth.

But unlike Earth, Mars lost its protective magnetic field, most likely due to the natural cooling of the planet’s interior. As the magnetic field collapsed, the solar wind began ravaging the planet’s surface, stripping away most of that CO₂ and water.

At this point, our story diverges from yesterday’s account. Little if any water was trapped underground. Mars managed to retain its polar ice caps, but that was basically it. Just a little ice—no liquid—beneath a dusting of frozen CO₂.

It’s hard to believe anything could have survived in this scenario, and yet life is resilient. Like many microorganisms on Earth, some Martian microbes could enter a state of suspended animation, waking up to feed and mate only when conditions become favorable to them.

Though the Martian atmosphere is thin, there’s enough atmospheric pressure to allow liquid water to exist within a narrow temperature range. During the Martian spring and summer, the polar ice starts melting, and the polar CO₂ starts sublimating.

The sudden influx of CO₂ into the atmosphere stirs up weather patterns, triggering Mars’s infamous sandstorms but also spreading minute traces of water from the poles to every corner of the planet’s surface.

Perchlorate salts, which are ubiquitous on Mars, have a way of sucking water right out of the air and trapping it in the Martian soil. And because they’re salts, they also lower water’s freezing point, expanding slightly the narrow temperature range in which liquid water can exist.

And so every spring and summer, as melt water trickles from the poles and is carried upon the Martian winds, Martian microbes emerge from their suspended animation and go into a frenzy of eating, breathing, and mating.

Most of these microbes live in the permafrost surrounding the poles, where seasonal melt water is a little more dependable. Others eek out an existence farther afield, perhaps even in and around the recurring slope lineae (RSLs) that we humans have only just noticed on the surface of Mars.

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Once again, this is a bit of a stretch. Could there really be enough seasonal melt water to sustain life on Mars? Maybe not, but as a science fiction writer, I can take a few liberties with the currently available scientific facts.

So which version of Mars is closer to the truth? Yesterday’s or today’s? It all depends on what we can learn from those RSLs. Does RSL water seep up from underground, or is it sucked out of the air by perchlorate salts?

If only we had some kind of robot on the surface of Mars, a robot equipped with an assortment of scientific instruments, a robot conveniently located near an RSL.

Turns out the Curiosity rover is just the robot we need, currently located within a few kilometers of a possible RSL site. But NASA won’t let Curiosity anywhere near it. Why not? We’ll find out in Friday’s edition of Sciency Words.

P.S.: In honor of Mars’s water, the above illustration of Curiosity traversing the Martian landscape is painted in watercolor.