A Dyson sphere is a hypothetical megastructure that encompasses a star and captures a large percentage of its solar power output. The concept is a thought experiment that attempts to imagine how a spacefaring civilization would meet its energy requirements once those requirements exceed what can be generated from the home planet's resources alone. Because only a tiny fraction of a star's energy emissions reaches the surface of any orbiting planet, building structures encircling a star would enable a civilization to harvest far more energy.
Mars, the fourth planet from the Sun, has appeared as a setting in works of fiction since at least the mid-1600s. Trends in the planet's portrayal have largely been influenced by advances in planetary science. It became the most popular celestial object in fiction in the late 1800s, when it became clear that there was no life on the Moon. The predominant genre depicting Mars at the time was utopian fiction. Around the same time, the mistaken belief that there are canals on Mars emerged and made its way into fiction, popularized by Percival Lowell's speculations of an ancient civilization having constructed them. The War of the Worlds, H. G. Wells's novel about an alien invasion of Earth by sinister Martians, was published in 1897 and went on to have a major influence on the science fiction genre.
A Type Ia supernova is a type of supernova that occurs in binary systems in which one of the stars is a white dwarf. The other star can be anything from a giant star to an even smaller white dwarf.
Jupiter, the largest planet in the Solar System, has appeared in works of fiction across several centuries. The way the planet has been depicted has evolved as more has become known about its composition; it was initially portrayed as being entirely solid, later as having a high-pressure atmosphere with a solid surface underneath, and finally as being entirely gaseous. It was a popular setting during the pulp era of science fiction. Life on the planet has variously been depicted as identical to humans, larger versions of humans, and non-human. Non-human life on Jupiter has been portrayed as primitive in some works and more advanced than humans in others.
Saturn has made appearances in fiction since the 1752 novel Micromégas by Voltaire. In the earliest depictions, it was portrayed as having a solid surface rather than its actual gaseous composition. In many of these works, the planet is inhabited by aliens that are usually portrayed as being more advanced than humans. In modern science fiction, the Saturnian atmosphere sometimes hosts floating settlements. The planet is occasionally visited by humans and its rings are sometimes mined for resources.
Pluto has appeared in fiction as a setting since shortly after its 1930 discovery, albeit infrequently. It was initially comparatively popular as it was newly discovered and thought to be the outermost object of the Solar System and made more fictional appearances than either Uranus or Neptune, though still far fewer than other planets. Alien life, sometimes intelligent life and occasionally an entire ecosphere, is a common motif in fictional depictions of Pluto. Human settlement appears only sporadically, but it is often either the starting or finishing point for a tour of the Solar System. It has variously been depicted as an originally extrasolar planet, the remnants of a destroyed planet, or entirely artificial. Its moon Charon has also appeared in a handful of works.
Asteroids have appeared in fiction since at least the late 1800s, the first one—Ceres—having been discovered in 1801. They were initially only used infrequently as writers preferred the planets as settings. The once-popular Phaëton hypothesis, which states that the asteroid belt consists of the remnants of the former fifth planet that existed in an orbit between Mars and Jupiter before somehow being destroyed, has been a recurring theme with various explanations for the planet's destruction proposed. This hypothetical former planet is in science fiction often called "Bodia" in reference to Johann Elert Bode, for whom the since-discredited Titius–Bode law that predicts the planet's existence is named.
Neptune has appeared in fiction since shortly after its 1846 discovery, albeit infrequently. It initially made appearances indirectly—e.g. through its inhabitants—rather than as a setting. The earliest stories set on Neptune itself portrayed it as a rocky planet rather than as having its actual gaseous composition; later works rectified this error. Extraterrestrial life on Neptune is uncommon in fiction, though the exceptions have ranged from humanoids to gaseous lifeforms. Neptune's largest moon Triton has also appeared in fiction, especially in the late 20th century onwards.
Uranus has been used as a setting in works of fiction since shortly after its 1781 discovery, albeit infrequently. The earliest depictions portrayed it as having a solid surface, whereas later stories portrayed it more accurately as a gaseous planet. Its moons have also appeared in a handful of works. Both the planet and its moons have experienced a slight trend of increased representation in fiction over time.
The fictional portrayal of the Solar System has often included planets, moons, and other celestial objects which do not actually exist. Some of these objects were, at one time, seriously considered as hypothetical planets which were either thought to have been observed, or were hypothesized to be orbiting the Sun in order to explain certain celestial phenomena. Often such objects continued to be used in literature long after the hypotheses upon which they were based had been abandoned.
Planets outside of the Solar System have appeared in fiction since at least the 1850s, long before the first real ones were discovered in the 1990s. Most of these fictional planets do not differ significantly from the Earth, and serve only as settings for the narrative. The majority host native lifeforms, sometimes with humans integrated into the ecosystems. Fictional planets that are not Earth-like vary in many different ways. They may have significantly stronger or weaker gravity on their surfaces, or have a particularly hot or cold climate. Both desert planets and ocean planets appear, as do planets with unusual chemical conditions. Various peculiar planetary shapes have been depicted, including flattened, cubic, and toroidal. Some fictional planets exist in multiple-star systems where the orbital mechanics can lead to exotic day–night or seasonal cycles, while others do not orbit any star at all. More fancifully, planets are occasionally portrayed as having sentience, though this is less common than stars receiving the same treatment or a planet's lifeforms having a collective consciousness.
Phaeton was the hypothetical planet hypothesized by the Titius–Bode law to have existed between the orbits of Mars and Jupiter, the destruction of which supposedly led to the formation of the asteroid belt. The hypothetical planet was named for Phaethon, the son of the sun god Helios in Greek mythology, who attempted to drive his father's solar chariot for a day with disastrous results and was ultimately destroyed by Zeus.
Stars outside of the Solar System have been featured as settings in works of fiction since at least the 1600s, though this did not become commonplace until the pulp era of science fiction. Stars themselves are rarely a point of focus in fiction, their most common role being an indirect one as hosts of planetary systems. In stories where stars nevertheless do get specific attention, they play a variety of roles. Their appearance as points of light in the sky is significant in several stories where there are too many, too few, or an unexpected arrangement of them; in fantasy, they often serve as omens. Stars also appear as sources of power, be it the heat and light of their emanating radiation or superpowers. Certain stages of stellar evolution have received particular attention: supernovae, neutron stars, and black holes. Stars being depicted as sentient beings—whether portrayed as supernatural entities, personified in human form, or simply anthropomorphized as having intelligence—is a recurring theme. Real stars occasionally make appearances in science fiction, especially the nearest: the Alpha Centauri system, often portrayed as the destination of the first interstellar voyage. Tau Ceti, a relatively-nearby star regarded as a plausible candidate for harbouring habitable planets, is also popular.
The Tunguska event—an enormous explosion in a remote region of Siberia on 30 June 1908—has appeared in many works of fiction.
Black holes, objects whose gravity is so strong that nothing—including light—can escape them, have been depicted in fiction since at least the pulp era of science fiction, before the term black hole was coined. A common portrayal at the time was of black holes as hazards to spacefarers, a motif that has also recurred in later works. The concept of black holes became popular in science and fiction alike in the 1960s. Authors quickly seized upon the relativistic effect of gravitational time dilation, whereby time passes more slowly closer to a black hole due to its immense gravitational field. Black holes also became a popular means of space travel in science fiction, especially when the notion of wormholes emerged as a relatively plausible way to achieve faster-than-light travel. In this concept, a black hole is connected to its theoretical opposite, a so-called white hole, and as such acts as a gateway to another point in space which might be very distant from the point of entry. More exotically, the point of emergence is occasionally portrayed as another point in time—thus enabling time travel—or even an entirely different universe.
Comets have appeared in works of fiction since at least the 1830s. They primarily appear in science fiction as literal objects, but also make occasional symbolical appearances in other genres. In keeping with their traditional cultural associations as omens, they often threaten destruction to Earth. This commonly comes in the form of looming impact events, and occasionally through more novel means such as affecting Earth's atmosphere in different ways. In other stories, humans seek out and visit comets for purposes of research or resource extraction. Comets are inhabited by various forms of life ranging from microbes to vampires in different depictions, and are themselves living beings in some stories.
"Message from space" is a type of "first contact" theme in science fiction. Stories of this type involve receiving an interstellar message which reveals the existence of other intelligent life in the universe.
The Sun has appeared as a setting in fiction at least since classical antiquity, but for a long time it received relatively sporadic attention. Many of the early depictions viewed it as an essentially Earth-like and thus potentially habitable body—a once-common belief about celestial objects in general known as the plurality of worlds—and depicted various kinds of solar inhabitants. As more became known about the Sun through advances in astronomy, in particular its temperature, solar inhabitants fell out of favour save for the occasional more exotic alien lifeforms. Instead, many stories focused on the eventual death of the Sun and the havoc it would wreak upon life on Earth. Before it was understood that the Sun is powered by nuclear fusion, the prevailing assumption among writers was that combustion was the source of its heat and light, and it was expected to run out of fuel relatively soon. Even after the true source of the Sun's energy was determined in the 1920s, the dimming or extinction of the Sun remained a recurring theme in disaster stories, with occasional attempts at averting disaster by reigniting the Sun. Another common way for the Sun to cause destruction is by exploding, and other mechanisms such as solar flares also appear on occasion.
Impact events have been a recurring theme in fiction since the 1800s.
Neutron stars—extremely dense remnants of stars that have undergone supernova events—have appeared in fiction since the 1960s. Their immense gravitational fields and resulting extreme tidal forces are a recurring point of focus. Some works depict the neutron stars as harbouring exotic alien lifeforms, while others focus on the habitability of the surrounding system of planets. Neutron star mergers, and their potential to cause extinction events at interstellar distances due to the enormous amounts of radiation released, also feature on occasion. Neutronium, the degenerate matter that makes up neutron stars, often turns up as a material existing outside of them in science fiction; in reality, it would likely not be stable.
