Once upon a time—four point six billion years ago—a thick atmosphere surrounded Mars, perhaps even coloring its sky blue. Once upon a time—three to four billion years ago—an ocean covered thirty percent of the Red Planet’s surface, and deltas formed as water rushed from the land to the sea. Once upon a time—as recently as 2 million years ago—Mars’ volcanoes, the largest in our Solar Systemmon, erupted, spilling lava down one hundred kilometer long slopes.

Once upon a time, Mars was lush and vibrant and geologically alive. But no more. Today, it hangs above us, red and dead in our dark, winter sky.

Time has been cruel to the Red Planet. Like Earth, Mars formed in the blast furnace of a much hotter, younger Sun, scorched dry by violent solar storms and radiation. It formed without water, but comets bombarded the young world, bringing rain pelting down from space. Images from the European Space Agency’s Mars Express spacecraft and NASA’s Mars Reconnaissance Orbiter show that the water carved out more than forty thousand riverbeds all across the Martian surface, and work lead by University of Colorado Boulder researcher Gaetano Di Achille indicates that it may have pooled into an ocean approximately one tenth the size of those on Earth.

But the ocean didn’t last. Mars, only about half the size of Earth, was born too small to stay wet or to hold onto its atmosphere. The angry, young Sun, raging against its planets, blasted them with cosmic rays and solar winds. Like the shields in a science fiction spacecraft, planets are protected from their suns by magnetic fields bending away the winds and rays. Mars’ magnetic field, however—generated by its molten core—was weak, as was its gravitational pull, which couldn’t stop the lightest atmospheric particles from leaving. One good collision—hydrogen on carbon dioxide—and these low-mass elements accelerated to escape velocities. Whoosh! Away they flew, depriving Mars of what little atmosphere it had. And the problem only escalated as the small planet quickly cooled, freezing out the molten core and further diminishing its already-anemic magnetic field.

The vicious cycle continued. Liquid water requires air. Without the pressure of air, water can boil away at room temperature, so as its atmospheric conditions shifted, Mars’ ocean soon began to disappear. Some of the water was locked up as ice underground. Some became part of the Martian atmosphere, freezing out each year to build the Red Planet’s distinctive icy poles. The water is still there, yes, but the seas are empty, now, and the riverbeds are nothing more than dry and desolate canyons.

But as we look at this desiccated world from our safe, verdant perch here on Earth, the question has to be asked: can Mars be revived? Can we bring back its youthful splendor through application of the proper, planetary treatments for aging? Can we make it habitable for humans?

Books like Kim Stanley Robinson’s Red Mars imagine the necessary steps: first, we’d need to create plants capable of surviving Mars’ horrible cold, horrible radiation, and its horribly thin atmosphere. Once that’s achieved, these plants would have to be cultivated across the planet’s surface so they could convert carbon dioxide to oxygen and carbon-sequestering plant matter. Also, we’d somehow need to melt the pole ice so that its carbon dioxide and water could supplement the still too-thin atmosphere.

But despite all this, despite whatever biological or botanical or chemical lengths we go to, the sad fact is that these measures can only do so much. Even if we could make Mars livable, we can never change its size. Mars, unfortunately, will always be too small to gravitationally keep an atmosphere and too cold internally to generate enough of a magnetic field to help it defend what little gas it has.

While some lichens might survive this re-loss of atmosphere, any plants adapted to the Martian geology would likely wilt away. Any newly planted greenery would die as the lack of atmospheric pressure allowed unconstrained water molecules to boil out. Over time, Mars would become an abandoned garden, withered gray and filled with desiccated crops.

So there it is: Mars is and will remain dead, geologically speaking, and any attempts to revive it would result only in a temporary resurrection.

However…

That’s not the whole story, because despite all the evidence to the contrary, this dead world may still be able to support life, though perhaps not the kind we’re used to.

In an exciting development, scientists working with data from Mars Express reported in August 2009 the presence of methane (a gas most commonly equated with cow flatulence) in the atmosphere of Mars. One particularly interesting property of methane is that it breaks down in sunlight, meaning that in order for it to be detected in the present, something must be generating it in the present. And the only two known possible sources for methane? Volcanism and life.

As mentioned earlier, Mars’ volcanoes are epic. They make Iceland look like a slightly smoky lump of rock. The largest mountain on Mars is Olympic Mons, a volcano that stands twenty-seven kilometers above the Martian surface. That’s sixteen miles high, three times the height of Everest. This geologic behemoth, the largest in our Solar System, offers us tantalizing hints at the possibility of both lava and life.

This shield volcano is geologically identical to the volcanoes of Hawaii, only, like Alice in Wonderland, it ate the cake and grew and grew and grew to gigantic proportions. Its caldera stretches across fifty-four lava-filled miles and shows evidence of eruptions as recently as two million years ago. In geologic terms, that’s recent history and means that it’s conceivable that present day volcanic activity, such as the venting of gases like methane, could be going on.

But let’s face it, as exciting as volcanoes are, alien life is a much more interesting possible explanation for the methane.

Here on our world, small bacteria called methanogens once ruled the surface of early Earth. These microorganisms rabidly metabolized carbon dioxide with molecular hydrogen to produce energy and methane waste. While not particularly cute or cuddly, these rod and ball shaped early life forms started off the long process of filling our world with life. Today on Earth, they are extinct, but maybe, just maybe, their cousins continue to live, output methane (without so much as an “excuse me”) and die on Mars.

However, like us humans, whatever form of alien life exists would probably need protection from radiation as well. But on atmospherically-challenged, magnetically-weak Mars, where could that shelter be found?

In those volcanoes, of course. Specifically, the lava tubes—long, hollow, underground stretches that once carried molten rock hundreds of kilometers down the mountains’ gently sloped flanks. Dirt and rock provide a remarkably good shield against radiation, and as the Martian surface became progressively more inhospitable, some scientists theorize that life could have retreated to the lava tubes, and other underground recesses, to survive.

So as far as any colonization plans go, those lava tubes could be the key to our future on Mars. The Red Planet’s surface is harsh and its atmosphere wispy, but underground, humans may find the safety we need to finally make our home on a planet other than Earth — provided, of course, that we’re willing to share the space with flatulent microbes.

While this isn’t quite the glorious, terraforming future dreamed of by generations of science fiction writers and readers, it is an achievable goal. And with a little luck, and a whole lot of hard work, it is, in fact, a dream we could conceivably make a reality within our lifetimes.

So…Mars-ward ho!