Life on Mars

Abstract

It’s one of the most interesting open questions in science: is there now, or has there ever been, life on Mars? Robotic rovers will surely someday give us the answer. Whatever that answer turns out to be, though, one thing is certain: the Mars of reality will be no match for the Mars of Weinbaum’s imagination.

Appendices

Commentary

Each year the Science Fiction Writers of America (SFWA) present Nebula Awards for the best SF novel, novella, novelette, and short story published in the preceding twelve months. The Nebula Award is a relatively recent invention (well it’s younger than I am, which in my mind makes it of recent vintage) so, in order to honour stories that predated the first Nebula Awards, the SFWA organized a poll to decide on the greatest SF published before 1965. The winner of the best short science fiction story generated no surprise: it was “Nightfall”, by Isaac Asimov. That “A Martian Odyssey” finished runner-up was perhaps more surprising—Weinbaum’s writing is, to put it kindly, of the standard one would expect from a story appearing in the July 1934 issue of a pulp magazine such as Wonder Stories. But the accolade was in truth well deserved. Asimov himself, in his introduction to The Best of Stanley G. Weinbaum, wrote that this tale of Martian adventure “had the effect on the field of an exploding grenade. With this single story Weinbaum was instantly recognized as the world’s best living science fiction writer, and at once almost every writer in the field tried to imitate him.” Weinbaum didn’t get the opportunity to be prolific; the cancer that killed him was likely establishing itself just as he was imagining the remarkable properties of the cart creatures’ cancer-healing crystal. But this single story of first contact with aliens sealed his fame. It remains one of the most important stories in the history of science fiction.

Although the story’s dialogue and plotting are dated, and its setting is unconvincing, Weinbaum’s vision of extraterrestrial life remains fresh. The story succeeds because of the sheer invention Weinbaum brings to his description of alien life forms. Indeed, there’s more of biological interest on his fictional Mars than there is here on Earth. As well as carbon-based flora and fauna there are organisms based on silicon—and those ancient, silicon-based pyramid-builders are wonderfully enigmatic. The dream beast is a fascinating and compelling creature—and even if its method of luring prey might not be physically possible it possesses a certain evolutionary logic. The cart creatures are immensely intriguing because they simply don’t care about humans—they have their own, unknowable motivations. And Tweel—well, Tweel is one of the great aliens in all of science fiction. The Mars of Weinbaum’s imagination would be a tremendous place for biologists to explore. Unfortunately, even before Weinbaum published his story, astronomers knew Mars was unlikely to be home to advanced life forms.

The nineteenth century had seen many speculations about Mars and the possibility of life. Telescopic observations had shown that Mars has ice caps, like Earth, which grow and shrink throughout the year; that Mars has seasons, like Earth; and that the Martian day is roughly the same length as Earth’s day. So in 1877, when Giovanni Schiaparelli observed patterns on the surface of the Red Planet and called them “canali”, many people were primed to think of Martian “canals” (the product of technology) rather than “channels” (the product of nature). In 1894, Percival Lowell set up the Flagstaff Observatory and spent much of the rest of his life investigating and popularizing the notion that an advanced Martian civilisation had built canals to transfer water from the ice caps to the rest of a drying, dying planet. Unfortunately for Lowell and his grand vision, in the same year he founded his observatory an American astronomer, William Wallace Campbell, discovered the Martian atmosphere contains neither water nor oxygen in anything other than trace amounts. This discovery didn’t prove life was absent on Mars—but it really didn’t boost the idea. Even worse, no one else could reliably see the markings that Lowell saw. And in 1909 astronomers trained the world’s largest telescope on Mars—and they saw not canals, or even channels, but irregular geological features. Those surface markings that Lowell painstakingly drew were just optical illusions. Nothing exists on Mars that resembles Tweel, the dream beast, or the pyramid-builders.

So “A Martian Odyssey” is not and never could have been a field guide to Martian zoology. But might the Red Planet be home to simple life? And even if it turns out the planet is barren now, might there have been simple life early in its history? These are interesting questions, which science is now on the verge of answering.

At the time of writing, space agencies have made 44 attempts to send craft—flyby missions and orbiters, landers and rovers—to Mars. (Of these missions, 21 have been US attempts; 18 have been USSR/Russian; Europe, India, and Japan have each sent one mission; and there have been joint European/Russian and Chinese/Russian missions.) One can gauge the difficulty of space exploration by noting that 23 of these attempts ended in failure and a further three can only be classed as partial successes. Nevertheless, despite the immense technical hurdles engineers must overcome, 18 missions have succeeded in studying Mars both at a distance (with orbiting satellites) and close-up (with surface rovers). The results are intriguing.

In January 2004, two Mars Exploration Rovers—Spirit and Opportunity—landed and began what was planned to be a 90-day research mission. Spirit continued its explorations until 2009, when it got trapped in soft soil and was no longer able to move; Opportunity, at the time of writing, continues to explore the Red Planet. The intriguing result is that both Spirit and Opportunity have found signs that liquid water once flowed on Mars. Furthermore the Curiosity Rover, which touched down in 2012 with a mission to explore the Gale crater, quickly found clear evidence for a fast-running stream that, aeons ago, flowed knee-deep through the region. The conclusion: a few billion years ago Mars was warm and wet. And where there’s water there’s at least the chance of life. When the solar system was still young might Mars have possessed an environment in which life could have flourished? (Fig. 4.1).

Fig. 4.1

A photograph taken by the Curiosity rover of a rock outcrop in the Gale crater. The outcrop (named Hottah) is exposed bedrock, which consists of small fragments that have been cemented together. Some of these fragments are rounded pebbles, the nature of which causes scientists to theorize that water once flowed across Gale crater. And where water flows there’s a chance of life! Even if there was once life on Mars, however, it surely would not have been as abundant as the flora and fauna that appears in Weinbaum’s “A Martian Odyssey”! (Credit: NASA/JPL-Caltech/MSSS)

To be clear: there is no evidence that any organism lives on Mars now. Mars and Earth followed different evolutionary paths. Since Mars is smaller than Earth it cooled more quickly, and its liquid iron–nickel core froze solid. Its magnetic field switched off, and with it vanished a protective shield that safeguards a planetary atmosphere from cosmic rays. Over time, as the Sun aged and brightened, Mars was stripped of its atmosphere. The Martian surface turned to rust. Spirit, Opportunity, and Curiosity are not encountering liquid water now. But billions of years ago there could have been liquid water flowing on Mars; the temperatures could have been rather pleasant; life—simple, microbial life—could have survived there, for a while at least. And if microorganisms did establish themselves on Mars then perhaps, even after all these billions of years, we might be able to find some traces that life left behind?

Some astrobiologists already claim to have found evidence for fossilised microbial Martian life—fossils found not on Mars but here on Earth! Allan Hills 84001, a 1.93 kg meteorite uncovered in Antarctica in 1984, was ejected from the Martian surface via meteor impact about 17 million years ago. It landed on Earth about 13,000 years ago. But the rock itself is old—it probably crystallised on Mars about 4 billion years ago, at a time when liquid water was abundant. In 1996, NASA scientists used a scanning electron microscope to study the rock. They saw structures—which they interpreted as being the fossils of incredibly tiny, bacteria-like organisms. Life! This interpretation has not been widely accepted by the scientific community. There are undoubtedly structures in AH84001 but they can be explained as crystallisations of organic molecules and minerals. We’d need much better evidence than this if we wanted to persuade ourselves we were looking at the remains of extraterrestrial life forms. Nevertheless, the fact such an interpretation is even possible surely means it’s worth contemplating what sorts of traces a primitive Martian biosphere might have left behind.

Consider, for example, Spirit’s discovery of the mineral opaline silica in the Gusev crater. The formation resembles cauliflower florets sprinkled over the Martian surface (see Fig. 4.2 top). More recently, geologists found similar-looking formations near geysers at the edge of Chile’s Atacama desert (see Fig. 4.2 bottom). Importantly, the environment at Atacama is about as close as you can come here on Earth to the Martian environment: the air is thin and dry, the Sun beats down with high levels of UV light, and the night is bitterly cold. So if it turns out the Atacama formations were created with the help of microbial life, as seems plausible, then perhaps microbes caused the Gusev formations? Of course, pointing out similarities proves nothing. To test the idea that microbial life caused the Gusev formations we’d need to analyse Martian samples in detail—but Spirit can’t help because it’s now stuck, presumed dead. Perhaps the next Martian rover will return to Gusev and investigate further. Even better would be if a craft were to travel to Mars, collect samples, and then return them to laboratories here on Earth for analysis. I’m sure one day this will happen.

Fig. 4.2

(Top) Mineral formations photographed by the Spirit rover in 2008, in the so-called Home Plate plateau in the Gusev crater on Mars. (Bottom) Hydrothermal mineral deposits near the El Tatio hotsprings in Atacama, Chile. The nodules here grew thanks to the activity of microorganisms. Visually, the cauliflower-like nodules in Atacama look similar to the nodules seen on Mars; could microorganisms have helped cause the Martian structures? (Credit: top—NASA/JPL-Caltech; bottom—Steve Ruff)

Within the solar system Mars is not the only place we might look for life. Titan, Saturn’s largest moon, is the site of complex chemistry that might conceivably harbour life. A more plausible candidate is Enceladus, another moon of Saturn, which potentially has lakes of liquid water beneath its frozen surface. And astrobiologists have postulated even more exotic places—the upper reaches of the Venusian atmosphere, the buried oceans of Jovian satellites—as being places to search for biology. But Mars remains our best bet for finding extraterrestrial life. Not extant life, necessarily, but at least signs of past life. Back when the solar system was young, Earth and Mars were alike; if life started here, it might have started there as well. Who knows—perhaps Mars was where Earth life started: it could have been transferred to a lifeless Earth by meteor.

After a period of investigation, of course, we might be forced to conclude that our neighbour is barren and always has been barren. That even though wet and warm conditions were once in place, life just didn’t start on Mars. Perhaps the first life on Mars will be us—when humans set foot there. And what if we learn that Earth, of all the places in the solar system, is the only home for life? Well, perhaps it hints that life—and in particular intelligent, self-conscious life—is rare. It would be wonderful to live in a universe where extraterrestrial life is as common and as strange as Weinbaum’s inventions, a universe in which we might try to communicate with non-human intelligences such as Tweel. But maybe the universe contains just us?

There is another possibility for non-human intelligence: perhaps humans, in their pursuit of ever more effective digital technologies, will develop artificial intelligence. This thought brings us nicely to Chapter 5.

Notes and Further Reading

• Asimov himself, in his introduction—See Weinbaum (1974).

• story of first contact with aliens—The question of “first contact” with alien beings is one of the key themes in SF. The story that gave the theme its name is “First contact” by Murray Leinster (1945), but Weinbaum’s story predates Leinster’s classic by almost a decade. Knight (1971) is an anthology of ten classic first-contact stories, including Leinster’s story, but it’s just one of many. Innumerable SF novels explore the theme of first contact, and it’s a popular idea in film and TV too: Star Trek, for example, wrestled with the problems and introduced the notion of a “Prime Directive”—the idea that space-faring civilisations should wherever possible avoid contact with technologically less advanced civilisations, because the latter might not be psychologically or culturally equipped to handle the shock of such an encounter.

• organisms based on silicon—As far as we know, the basic structural and metabolic functions of all living organisms on Earth are based on carbon compounds. Does it necessarily follow that the structural and metabolic functions of all living organisms everywhere in the universe are based on carbon? There are two good reasons why it might. First, carbon is relatively abundant; it is the fourth most abundant element in our galaxy. Second, when it comes to chemistry, carbon is extremely versatile: it can form single, double and triple bonds, along with chains, branched chains, and rings … it provides life with rich opportunities to try out many different types of complex compound. On the other hand, there are elements that resemble carbon. In particular, silicon sits directly below carbon in the periodic table of the elements—so it isn’t too outrageous to postulate an alternative biochemistry based on silicon. Indeed, the first such suggestion was made as long ago as 1891, by the German astronomer Julius Scheiner. The idea proved popular, and soon the great SF author H.G. Wells (1894), writing in a non-fiction article, remarked of the hypothesis that “one is startled towards fantastic imaginings by such a suggestion: visions of silicon–aluminium organisms …”. To the best of my knowledge, however, Weinbaum’s “A Martian Odyssey” is the first appearance in SF of the notion of silicon-based life.

  Although it might demonstrate appalling carbon chauvinism, I believe most biologists would agree that silicon is unlikely to be the basis of an alternative biochemistry. Silicon, for one thing, just doesn’t have the same versatility as carbon. Perhaps our mastery of silicon chip technology will advance to the stage where we must grant that our robots are “alive”; in that case we might reasonably talk of silicon-based life. But it seems unlikely that a living silicon-based organism will develop through natural processes.

• speculations about Mars and the possibility of life—Sheehan (1996) is my favourite account of the evolution of astronomers’ understanding of the Red Planet. For an entertaining, short account of Lowell’s interest in Mars see Zahnle (2001).

• space agencies have made 44 attempts—For a list of the 44 missions to Mars, along with their fate, see NASA (n.d.). This website gives details of a 45th mission—the Mars InSight Lander—which, at the time of writing, is on its way to the Red Planet but still has 5 months’ travel before it reaches its destination.

• two Mars Exploration Rovers—Squyres (2006) gives a first-person account of a NASA scientist’s work on the Mars Exploration Rover mission. Pyle (2014) is a science writer’s view of the Curiosity mission, while Manning and Simon (2017) gives the story of Curiosity from inside NASA—Rob Manning was the mission’s Chief Engineer. These books are highly recommended for those who want to learn more of the difficulties involved in exploring Mars, and how scientists and engineers have overcome them.

• Some astrobiologists already claim to have found evidence—For the fascinating story of meteorite AH84001, and the scientific, political, and media debate it inspired, see Sawyer (2006).

• geologists found similar-looking formations—For further details, see Ruff and Farmer (2016).