Our place in space

More than 300 years before Apollo 11, the astronomer Johannes Kepler wrote a science-fiction fantasy, Somnium, in which a mother and son journey to the Moon and describe the appearance of the Earth from there, complete with observed “phases” akin to the Moon’s own. The purpose was partly science communication: Somnium’s depiction of the Earth orbiting the Sun was an attempt to persuade the reader of the correctness of the then revolutionary Copernican principle, as supported and developed by Galileo’s discovery of Jupiter’s moons and by Kepler’s laws of planetary motion. And if the planets orbit the Sun, then the logical inference is that other stars might have their own “exoplanets”, as suggested by Giordano Bruno in 1584.

The first exoplanet orbiting a Sun-like star was discovered in 1995 and more than 5,800 have been detected to date, the majority as a result of Nasa’s Kepler mission, which operated for almost ten years from 2009. But very few of these exoplanets have been directly imaged: for the majority, we know nothing other than their total masses, densities and orbits. Most of them are gas giants, similar to Jupiter, but orbiting far closer to their stars than Jupiter. This unexpected observation is problematic, according to the standard theory of planetary formation: gas giants should not be able to form close to a hot star without evaporating first. None so far has been shown to be like Earth, with the apparent prerequisites for life of liquid water, a magnetic field and an atmosphere, but this doesn’t mean that life can’t form in other ways and on other types of planets. It has also become clear that exoplanets are far, far more common than was assumed prior to the Kepler mission. There might be billions in our galaxy alone.

It’s this gap in knowledge, and the potential for a philosophical, as well as scientific, game-changing challenge to our understanding of our place in the Universe, that science fiction is ideally positioned to fill. Exoplanets make a regular appearance in science fiction, perhaps the most famous examples being the desert planets Tatooine in Star Wars and Arrakis in Dune. Keith Cooper’s book summarizes recent advances in our understanding of exoplanets and compares them to fictional planets in books and films, in an attempt to determine to what extent science fiction has been influenced by actual science, and whether these fictional worlds are based on real observations and scientifically plausible.

Each chapter of Amazing Worlds of Science Fiction and Science Fact describes a different category of fictional exoplanet, including desert planets, water planets, snowball planets, planets with more than one sun and city-planets, then compares them to known data. Tidally locked planets are those where only one side faces the star, and the other is permanently turned away (just as we only see one side of the Moon because it is tidally locked in orbit around Earth). In The City in the Middle of the Night by Charlie Jane Anders, the city on such a planet is located in the thin ribbon of permanent twilight between day and night, which are better defined as places than as times. “Habitable zones’”were originally conceived as minimum and maximum planetary orbits around stars in which the temperature allowed water to remain liquid. But science fiction has clearly responded to astronomers’ realization that life might develop in relatively small niches in otherwise inhospitable terrains. Alastair Reynolds’s novel Chasm City, for example, describes how life can be situated in a deep crevasse on an otherwise barren planet.

Astronomers know that they may still be hampered by an assumption that life “out there” resembles life on Earth, meaning that they are searching for the wrong chemical signals and failing to conjecture fundamentally different forms. Progress depends on the James Webb Space Telescope, which has the capability to measure the chemical composition of planetary atmospheres. This science of “amazing worlds” will likely alter beyond all recognition in the near future.

There is a cyclical relation of sorts between astronomers and science fiction authors (even an overlap in the case of Reynolds, who has a PhD in astronomy). Keith Cooper mentions a nice piece of quantitative analysis by researchers at the University of St Andrews showing that authors have responded to the age of exoplanet discovery and the unexpected prevalence of “hot Jupiter” gas giants by exploring fictional alternatives to the cliché of rocky Earth-like planets. In turn, the astronomers interviewed here comment that reading or watching science fiction when they were young influenced their career choice. This book shows how science and science fiction play leapfrog with each other.

Pippa Goldschmidt is co-editor of Uncanny Bodies, 2020. Her books include Night Vision, 2024

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