Destination: Mercury

There is no better example of how science fiction’s tendency to try and imagine a plausible future is like throwing a dart at a moving target than Larry Niven’s 1964 short story “The Coldest Place.” Up to that point, astronomers widely believed that the planet Mercury was tidally locked to the Sun: its rotation matched that of its orbit and as a result, only one side ever faced the Sun, meaning that its dark side would have been much cooler. Niven took that bit of knowledge and incorporated it into his story—his first—and sent it off to Frederik Pohl’s If, where it appeared in the December 1964 issue.

It was during the 1960s that the space race hit its stride, and while the Apollo missions to the Moon took up much of the attention of the general public and scientific community, there were plenty of scientists who were keenly interested in researching the nature of the solar system’s other bodies, including Mercury. In 1962, astronomers from the University of Michigan first observed our solar system’s smallest planet with a radio telescope and discovered something unexpected: the side facing away from the Sun was warmer, indicating that the planet wasn’t tidally locked. Further studies a couple of years later confirmed the finding: for every two Mercurian years (one year being the equivalent of eighty-eight Earth days), it experienced three Mercurian days (each rotation on its axis a bit under fifty-nine Earth days).

Niven’s story was no longer scientifically accurate.

Messenger to the Gods

Ancient astronomers from all over the world have long been able to detect our solar system’s rocky bodies, and through centuries of observations, have incorporated them into their respective cosmologies. As these various ancient cultures charted the movements of our solar system’s most prominent astrological feature—the Sun—they took notice of another object that was closely associated with it: Mercury. According to NASA, Mercury popped up in Babylonian star catalogs, and that they named it Nebo/Nabu—a god of writing and records, and who served as a messenger to the gods. Mercury was often to be seen during the morning and evening hours, when the Sun’s glare wouldn’t overtake it. Greek astronomers also assigned Mercury with the role of messenger for its apparent speed. They called it Hermes, a quick-moving messenger to the gods who served as a conduit between the mortal and divine worlds who moved on winged sandals. Roman theology echoed that of Greece’s and named the god Mercury.

Over time, ancient astronomers shifted their understanding of the cosmos. Writing in The Human Cosmos: Civilization and the Stars, Jo Marchant writes that astronomer Ptolemy wrote an influential text on the nature of the cosmos, seeking to organize it into a rational system. But more importantly, he “differed from the Babylonians in that rather than seeing celestial signs as divine warnings, he believed powers emanating from the stars and planets, such as ‘humoral shifts’ could trigger effects on Earth, influencing everything from the weather to personality and health.” It was a line of thinking that still persists to this day, an idea that links our everyday lives with that of the cosmos above us. He believed that Mercury danced just beyond the orbit of the Moon. Chinese scholars associated the planet with water, while Northern Europeans claimed it for Odin.

That thinking would again shift with time as new philosophers and thinkers like Copernicus and Galileo reset our thinking on the nature of the solar system: that the Sun was the center of our system, rather than the Earth, and that our home planet and its neighbors orbited it.

A Rational Cosmos

The development of the telescope brought the cosmos closer to early astronomers, and with it, a seismic shift in our understanding of our stellar neighborhood. The 1500s brought with it a series of early scientists who began to develop a heliocentric view of the solar system. Danish astronomer Tycho Brahe made several critical observations of supernovae and comets that revealed that the universe was much larger than previously thought and began to think that while maybe the Sun and Moon might revolve around Earth, the other planets might not. His protégé, Johannes Kepler, built upon his work and devised his three laws of planetary motion, which provided a model for how the objects in the solar system operated.

The scientists who followed were able to directly observe Mercury. Using his calculations of planetary motion, Kepler predicted in 1627 that both Mercury and Venus would transit the Sun in 1631. Unfortunately, Kepler died in 1630 and wasn’t able to make the observation himself. But others did: a French astronomer and priest named Pierre Gassendi projected an image of the Sun through his telescope in a dark room and was able to see the tiny dot of Mercury cross the face of the Sun, and a couple of weeks later, viewed Venus doing the same. He recognized that the planets were much smaller than expected: Mercury was tiny, the smallest of the rocky planets. At least two other astronomers witnessed the transit, and others would follow. Italian astronomer Giovanni Zupi recorded Mercury’s phases (proving that the planet was indeed orbiting the Sun), and in 1676, English astronomer Edmond Halley traveled to the island of Saint Helena in the Atlantic Ocean, where he recorded a Mercurian transit.

This new understanding of the solar system provided astronomers with the ability to better understand the true nature of the universe—a rational, understandable, and observable world. Scientists weren’t the only ones drawing inspiration and insight from this mindset: the forerunners to the modern science fiction genre were also interested in the developments and changes of the world. The Encyclopedia of Science Fiction notes that the first work to feature Mercury was likely Athanasius Kircher’s 1656 work Itinerarium Exstaticum, in which a man named Theodidactus is carried along on a journey through the solar system by an angel, Cosmiel.

Mercury was also “generally included in other round tours of the planets,” writes Brian M. Stableford and David Langford in The Encyclopedia of Science Fiction. Those works appeared in the coming decades, such as Emanuel Swedenborg’s The Earths in Our Solar System, George Griffith’s A Honeymoon in Space, and John Munro’s A Trip to Venus, while Le Chevalier de Béthune’s Relation du Monde de Mercure (translated as The World of Mercury) appears to be the first novel in which Mercury was the main setting.

With the help of telescopes and new orbital models, astronomers were able to get a better look at the nature of the planet throughout the 1800s. In the 1840s, French astronomer Urbain Le Verrier noted that there was a tiny discrepancy in Mercury’s orbits around the Sun: it seemed to be a little slower than could be accounted for. He theorized that there could be another, smaller body orbiting even closer to the Sun—something small enough to mess with Mercury’s orbit just enough to account for the slight delay. He attempted to track the theoretical planet down (he was good at this: he was the one who calculated the existence of Neptune before it was directly observed), working off of potential sightings from other astronomers, but in the years that followed, no such planet turned up. It wasn’t until 1915 when the discrepancies in the calculations were solved with Albert Einstein’s theory of relativity. Since then, scientists have theorized the possibility of an asteroid belt or planetoid orbiting between Mercury and the Sun—Vulcanoids—although none have been discovered as of yet.

But while Venus and Mars sparked the imagination of authors and storytellers throughout history, Mercury was largely overlooked. Part of this seems to have come down to size, location, and disposition. Venus provides a brilliant presence in the night sky; Mars shows up in grim red tones. Venus is nearly the same size as Earth, and its thick atmosphere shrouds its surface in mystery, while astronomers and the general public were mesmerized by Mars’ features, such as its channels, which were sensationally mistranslated as “Canals.” That intrigue led to both Mars and Venus as central destinations for the minds of early science fiction authors, such as H. G. Wells or Edgar Rice Burroughs, who told sensational stories about alien civilizations and lost ruins, and the adventurers who encountered them.

World of Extremes

Mercury, given the more limited opportunities to view it, seems to have avoided that treatment, although The Encyclopedia of Science Fiction points out that the early pulp magazines included stories set on the planet by Homer Eon Flint, Ray Cummings, and Clark Ashton Smith during the modern genre’s formative years.

Scientists were discovering that Mercury’s nature likely led it to be an inhospitable location for life: over the course of his career, Italian astronomer Giovanni Schiaparelli used telescopes to map the surfaces of Mars and Mercury (he’s the one who named Mars’ surface features “canali”—leading to the idea that they were artificial channels, and thus life was there), and while mapping the surface of Mercury, he theorized that the planet was tidally-locked to the Sun: a day and a year were one and the same, and thus, only one of Mercury’s sides was exposed to the Sun’s intense light and radiation, while the other was left inhospitably cold. It’s an idea that stuck within the scientific community for decades, and the planet’s harsh extremes provided plenty of material for authors to play with as science fiction began to form as a distinct genre.

As the world entered the twentieth century The Encyclopedia of Science Fiction notes stories with real scientific and realistic rigor were rare—but not unheard of—prior to World War II.

One early example is Clifford D. Simak’s story “Masquerade” (published in Astounding Science Fiction’s March 1941 issue), which featured a group of astronauts using the planet as a base for collecting solar energy and running afoul of some of the planet’s native inhabitants. Isaac Asimov’s early Robot story “Runaround” (published in Astounding Science Fiction’s March 1942 issue) put Mercury’s hostile environment front and center. “The photocell banks that alone stood between the full power of Mercury’s monstrous Sun and themselves were shot to hell,” Asimov wrote, introducing a ticking clock story as the two astronauts figure out how to fix a malfunctioning robot before they were cooked to death by the Sun’s heat.

Other stories that followed often set Mercury as a destination for stories of endurance, such as Alan E. Nourse’s “Brightside Crossing” (published in Galaxy magazine’s January 1956 issue), in which an adventurer named James Baron planned a daring four thousand-mile trek across the planet’s bright side. “I want to make a Crossing at perihelion and I want to cross on the surface,” says Major Armstrong, “If a man can do that, he’s got Mercury. Until then, nobody’s got Mercury. I want Mercury—but I’ll need help getting it.” Nourse explicitly highlights Mercury’s rotational spin and describes the adventure as a “hellish trek.”

Hugh Walters set his short novel Mission to Mercury on the planet in the same year and draws on that dual hot-and-cold nature as an expedition runs into trouble and is forced to touch down on the far side—where they risk freezing to death. Other authors, such as David Brin (Sundiver), Arthur C. Clarke (Islands in the Sky, Rendezvous with Rama), Hal Clement (Iceworld), Gordon R. Dickson (Necromancer), and Kurt Vonnegut (The Sirens of Titan), utilized the planet as a location over the years.

Niven’s “The Coldest Place” follows a character who’s searching for alien life on the planet, and ultimately captures one that’s composed of a type of helium. But the story is best known for the abrupt shift as the reality underpinning the story is changed by new discoveries.

In this case, astronomers using radar and radio telescopes discovered that the long-held assumptions about the nature of Mercury weren’t accurate: the planet did rotate, but slowly. These discoveries were later confirmed as NASA dispatched a probe, the Mariner 10, in 1973. The spacecraft performed a trio of flybys of the planet between 1974 and 1975, taking photographs of half the planet’s surface and utilizing an array of sensors, including a charged particle telescope, an infrared radiometer, magnetometers, plasma detectors, ultraviolet spectrometers, and others to measure the planet’s radiation, magnetosphere, and other characteristics, giving scientists and science fiction authors their best look yet at the planet.

What it found was a hellish world, pockmarked with craters, and surprisingly, a strong magnetic field, and that it was home to a thin atmosphere composed of helium.

As was the case before, science fiction largely ignored Mercury. Its proximity to the Sun meant that it was too difficult to terraform like Mars or Venus, and as The Encyclopedia of Science Fiction points out, “recent SF employs Mercury as merely a convenient place to site bases for studying the Sun.” In 2005, Ben Bova set one of his Grand Tournovels, Mercury, about an entrepreneur named Saito Yamagata, who plans to set up a solar-harvesting operation to power deep space starships, on the planet. In 2008 and 2012, Charles Stross and Kim Stanley Robinson respectively imagined massive, tracked cities that traveled around Mercury in tune with its rotation, keeping their inhabitants out of the harsh Sunlight, demonstrating that humanity could adapt to even the most inhospitable regions of the solar system. It’s also been fleetingly seen in film and television—Danny Boyle’s 2007 film Sunshine saw an expedition to restart the Sun and stop by the planet to meet up with a sister ship, hiding behind it from the Sun’s energy, as well as the occasional visit in shows like Star Trek, Futurama, Invader Zim, and a handful of others, with varying degrees of realism.

The most recent visitor to the planet was MESSENGER (Mercury Surface, Space Environment, Geochemistry, and Ranging), a NASA probe that was launched in 2004, and which arrived in 2011 to further study the planet after Mariner 10. Unlike its predecessor, it was able to map Mercury’s entire surface, sending back stunning pictures of the planet’s pockmarked surface, and gathering information about the planet’s composition, the nature of its magnetic field, that the planet appeared to be tectonically active, and something surprising: that the planet was home to water ice and organic compounds, hidden in shaded craters at the planet’s north pole. The mission came to an end in 2014 when the probe ran out of fuel and crashed onto the surface in 2015.

While Niven’s story has been reduced to a handy demonstration about the changing nature of our understanding of space and the universe, Mercury itself offers up plenty of examples of the same: observations of the planet helped to better firm up our understanding of the nature of our solar system, and more recent scientific missions have demonstrated that we should be careful with any firm assumptions that we might have for the little planet: MESSENGER’s discovery of water and ice hidden deep in craters shows that there are plenty of surprises waiting for us, and which could provide plenty of inspiration for future authors who want to stop by the world for visits in the future.