The Sirens of Mars: Searching for Life on Another Planet

Valles Marineris, the 4,000-kilometre canyon ripping through the Martian equator

The insistent call of the red planet, our neighbour, yet utterly alien, is well expressed by the title of Sarah Stewart Johnson’s lyrical book The Sirens of Mars.

Johnson, a planetary scientist at Georgetown University who has contributed to several of NASA’s recent Mars missions, including the ongoing Curiosity Rover programme, considers the hopes and fears Mars has inspired since ancient astronomers wondered at an enigmatic red star shimmering on the horizon.

It’s a deeply personal work, at times reading like spiritual autobiography, a history of Martian exploration interwoven with episodes from the life of a writer whose vocation has been driven by fascination with the ‘wild strangeness of the planet, with its tawny air and relentless red deserts’. For Johnson, the mystery of Mars is emblematic of the enigma of life itself, the disclosure of its secrets a key to our place within the cosmos.

The home of the west wind

Since first coming into focus as a new world through the gaze of Galileo’s telescope, the planet has been a canvas for the imaginations of generations of astronomers, artists, composers and writers.

The desire to project our hopes and fears on the Mars was exemplified by the efforts of the 19th century Italian astronomer Giovanni Schiaparelli to make a heaven of the planet, who bestowed it with the beautiful names drawn from classical and biblical mythology that have resonated through the history of space exploration and science fiction.

‘First,’ Johnson writes in one of her book’s many evocative passages, ‘he cleaved the globe with a giant diaframma, a north-south dividing line between the darker and lighter areas. He split the bright areas into a drove of islands and gave them names like Zephyria, the home of the west wind; Argyre, a mythical island; and Elysium, the land of dead heroes. To the west, inside the Columns of Hercules, he mapped the dark seas: Mare Tyrrehenum, the sea of the Etruscans; Mare Cimmerium, the sea of the Thracians; and Mare Sirenum, the sea of sirens. To the north were the stomping grounds of Arcadia, and to the east was Solis Lacus, the lake of the sun.’

Schiaparelli also projected the darker elements of his psyche onto the planet, the ‘black melancholy’ to which he was susceptible immortalised in the names he gave to regions such as Memnonia, a leaden patch that whitens during the Martian winter.

Schiaparelli also gave new impetus to the persistent belief that the planet was home to intelligent life. For the 17th century Dutch physicist Christiaan Huygens, to consider the planets ‘nothing but vast Deserts, lifeless and inanimate Stocks and Stones’ would be to sink them ‘below the Earth in Beauty and Dignity — a thing that no reason would permit.’ And Isaac Newton assumed the Martians ‘probably enjoy a situation in many respects similar to our own.’

Detail from Giovanni Schiaparelli’s Mars map

The ‘wave of darkening’

Schiaparelli’s observation that the planet appeared to be criss-crossed by lines inspired the gentleman astronomer Percival Lowell’s notorious theory that Mars was mapped by an intricate network of canals. Lowell believed the suggestion made sense of several phenomena that had puzzled astronomers, notably the shadows that crept across the surface during the Martian spring. This ‘wave of darkening’, Lowell reasoned, was a sheen of vegetation that spread from seasonal overflow of the canals just as, on Earth, the Nile Delta turns green.

From these speculations Lowell evolved an intricate and influential theory of Martian civilisation. The gradual drying of the planet’s climate necessitated the construction of a system of waterways to distribute water from the polar snows, an engineering feat that could only have been achieved by a technologically and ethically advanced society with the wisdom to apply scientific knowledge for the common good.

Though disputed by mainstream astronomers even at the time, Lowell’s speculations inspired the great political science fiction written around the turn of the century. The ruthless Martians of HG Wells’s The War of the Worlds with ‘intellects vast and cool and unsympathetic, regarded this earth with envious eyes, and slowly and surely drew their plans against us’, whereas the enlightened socialists depicted in Alexander Bogdanov’s Red Star refrain from invading a planet with a less sophisticated civilisation even in the knowledge that their own world is dying.

A world of storms, fossilised

But the notion that Mars hosts an advanced society, or indeed any kind of surface life, has disintegrated over past century as more powerful telescopes have evolved, and, since the 1960s, probes and landers have crossed the void to survey the planet. Since Mariner 4 sent back the first grainy images of the surface in 1965, using transmitters no more powerful than a couple of lightbulbs to send back pictures across 40 million miles of space, the image of a forbidding world utterly different from Earth has become ever sharper.

There are no canals here, no rivers, lakes, oceans or seas. It hasn’t rained for at least two billion years. Lowell’s canals are canyons, mountain ranges, and strings of craters, the visual illusions of great distance. The ‘wave of darkening’ is no flowering of the Martian desert but the effect of periodic shifting of the regolith, the planet’s coating of fine red dust, partially exposing the dark rocks below. No banks of clouds pass through skies somewhat like our own: the Martian daytime never lightens beyond an eerie crepuscular glow. There is no shifting of tectonic plates, as on Earth, where the surface is churned and renewed over millennia. ‘Mars’, as Johnson puts it, ‘is all past’, a fossil hanging in space, unchanged for the past three billion years. Until our landers and robots arrived the planet was utterly silent, disturbed only by the waxing and waning of the polar caps, the meteorites that cleave through the defenceless atmosphere, and the great dust storms that spiral in response to seasonal warmings of the planet’s surface. And the brutal findings of the 1976 Viking lander showed not only that there is no terrestrial life on Mars, but that there can be no life. The planet is forever battered by cosmic radiation that saturates the soil with oxidants that corrode complex chemistry.

Our close encounters with the planet have been revelatory, and chastening. Mars is truly alien, but not in the way we had imagined. It is a giant tomb, the ‘dry Mars’ described in the science fiction of Ray Bradbury, Arthur C Clarke and Kim Stanley Robinson. But it wasn’t always so. The spectacular landscapes mapped in exquisite detail by the probes and landers missions were shaped by a Mars that was — a long, long time ago — very different.

This was once a febrile world of storms. Mars is studded with some of the largest volcanoes in the solar system: Olympus Mons stands 20 kilometres high, the platform from which it begins to rise itself towering over Everest. The Valles Marineris, the 4,000-kilometre canyon ripping through the equator, is nearly five times as deep as Africa’s Great Rift Valley, with side channels big enough to engulf the Grand Canyon. There are great beds and basins where ancient rivers ran and oceans gathered — the Hellas Basin is deep enough to engulf Mount Kilimanjaro.

The tumultuous ancient Mars that left such dramatic traces was not so far from some of the dreams that pre-dated our era of space exploration. William Henry Pickering, Wells and Bogdanov’s contemporary, had imagined an uninhabited primordial wilderness, a mountainous land of thunderstorms and wave-lashed coasts, cumulus clouds blooming in luminous skies after torrents of midnight rain.

And, indeed, some three to four billion years ago, before, as Johnson puts it, the planet ‘rusted over’, Mars was as wild as the early Earth. The black igneous rock below the regolith was formed through the cooling and solidification of lava generated by volcanoes that, in turn, produced greenhouse gases that condensed to form oceans. Basalt broiled and surged under the Martian crust, slicing it open and burning the great valleys and canyons we see today into the planet’s surface. The layers of sediment forming the ancient river beds studied by the lander robots were worked and reworked by ancient winds and salt seas. The northern plains, among the smoothest surfaces in the solar system, were once the abyssal plains of great oceans. The Martian atmosphere may never have been strong enough to allow a biosphere to develop by photosynthesis, as on Earth, but primitive life may have been able to flourish below the surface.

And it may still be there. The exploration of our own planet’s remote environments that has run in parallel to the Martian expeditions keeps finding cellular life that can survive the harshest environments. Thriving microbial communities able to insert themselves into tiny rock pores have been found in hydrothermal vents with toxic sulphide gas on the deep sea floor, and embedded in the radioactive waste of nuclear reactors. If life developed on ancient Mars, the planet’s subsurface actually offers a more hospitable environment than that of Earth for the survival of bacteria, due to the relatively light gravity that makes its rocks more porous.

Indeed for a brief period in the late 1990s evidence of just such life had seemingly fallen to Earth. Close examination of rock ALH84001, a fist-sized meteorite discovered in Antarctica that had been flung from the Martian subsurface, revealed a rock notable for its age — it appeared to have formed only fifty million years after the of the solar system — and the delicate magnetite crystal patterns that threaded through it, similar to those produced by microbes on Earth.

And there was something else: a shape resembling a nanobacteria fossil, perhaps the trace of microbe that once floated through ancient Martian seas. For a moment, writes Johnson, ‘we held in our hands what we had been after for so long: a Rosetta stone for biology’, a key to whether there are universal laws of biology, as with physics and chemistry, or whether biochemistries are unique to particular environments. That hope was shut down just months later, subsequent study showing that whatever organic material the rock had housed was likely to have seeped in with the Antarctic meltwater.

Detail of meteorite ALH84001

The primal planet

Despite the search for life on Mars being pushed ever deeper into the planet’s recesses, Johnson continues to hope: ‘Maybe there we’ll discover an underground mausoleum, some single-celled version of the catacombs beneath Paris.’ Maybe. As The Sirens of Mars unfolds her sense of wonder is shadowed by the planet’s forbidding silence. This is a sublime, terrifying place.

By the end of the book her quest is as much spiritual as scientific. Evidence of any life, no matter how simple would be ‘a rebuke to the cratered image of Mars, the acid waters, the sterile soil’, a chance ‘to discover the smallest breath in the deepest night and, in so doing, vanquish the void that lurked between human existence and all else in the cosmos.’ The book’s afterword reveals that its yearning tone, and acute sense of life’s fragility, was sharpened by Johnson’s succumbing to a near fatal illness while completing the manuscript.

That seriousness, and her profound respect for the particularity of another world, sets her essay apart from so much contemporary Mars writing suffused with breathless anticipation about the possibilities of crewed spaceflight, colonisation and terraforming.

At its best that writing communicates understandable excitement that modern technology seems on the verge of being good enough to allow us to visit the planet in person. At its worst blithe speculation that Martian colonisation will offer us ‘a new home’, ‘a second chance’ or ‘a backup option’ is the most sheer escapism, wilfully downplaying the fearsome challenge of establishing even the most modest of settlements in such a relentlessly hostile environment, and distracting us from the pressing task of trying to make our life here on Earth sustainable. Promethean projects like Space X both thrill and repel, our natural fascination with cutting-edge space technologies tempered by the wide-eyed relish for the possibility of ’escaping’ Earth they encourage.

Johnson fears that attempts at settlement will despoil the purity of the the Martian wilderness, the book at time recalling the sentiments of the ‘Red’ party in Kim Stanley Robinson’s Red Mars trilogy that seeks to protect the integrity of the planet from the depredations of colonisation and terraforming. Robinson’s geologist Ann Clayborne muses on the ‘primal planet, in all its sublime glory, red and rust, still as death; dead; altered through the years only by matter’s chemical permutations, the immense slow life of geophysics. It was an old concept — abiologic life — but there it was, if one cared to see it, a kind of living, out there spinning, moving through the stars that burned’.

And like Robinson, Johnson is wholly unsentimental regarding the absolute hostility of the Martian environment to human life. The thin atmosphere makes it difficult even to land — we still only have a 50 percent success rate for landing robotic landers. There almost nothing to make a home with, frozen water only existing in quantity in the polar regions. The planet is cloaked with red dust much finer than our native sand, able to seep into the smallest crevices in machinery, and frequently blowing up into great storms. And Mars is poisonous, bombarded by a ceaseless rain of radiation severely limiting the time humans could spend on the surface.

It does seems that a crewed mission is now technically possible. But if we are going to establish a base on Mars the best we might hope for is a new Antarctica rather than a new Atlantis: any Martian settlement is much more likely to resemble the kind of research stations we maintain in Earth’s polar wastes, where small teams of scientists work for a couple of years before returning, rather than great domed cities twinkling under the stars. Quite simply we do not yet know how to maintain balanced artificial biospheres of the type we would rely upon on Mars for any duration: closed systems are always unbalanced by the new, unanticipated forms of life they generate.

The Sirens of Mars is an intelligent contribution by a writer keenly sensitive to the integrity and difference of our neighbouring planet, so near and so profoundly distant. Describing the last moments of one of the Martian landers, Johnson writes: ‘Before Phoenix died, the instruments recorded falling flurries: water-ice crystals floating gently from high, thin clouds. … No one ever knew it snowed on Mars, and now it’s forever known — a final gift from the spacecraft, a small piece of the permanence of the universe that we don’t share in. … But if you were there on Mars, looking up from Vastitas Borealis, it would have been enough to make the sky sparkle.’

It’s a passage that captures the strangeness of another world: beautiful, frightening, wholly other.

Martian sunset recorded by NASA’s Curiosity Rover

The Sirens of Mars: Searching for Life on Another World by Sarah Stewart Johnson is published by Allen Lane.



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