Kryptonians: Why Superman Has Powers on Earth and What Destroyed Krypton

The first alien to reach a mass American audience was a baby in a rocket. Action Comics #1, dated June 1938, opens on a distant planet destroyed by old age, a scientist placing his infant son in a hastily built ship, and the ship landing on Earth; Jerry Siegel and Joe Shuster, two young men from Cleveland, had spent five years failing to sell the character before that page. Krypton was named in the strip's first newspaper run in 1939 and drawn over the next decades as a crystalline, scientifically advanced, socially rigid world orbiting the red giant Rao, with a Science Council that ran everything and a habit of not listening to Jor-El. The planet's look has changed with each generation: the 1978 film gave it Marlon Brando and a landscape of white crystal, Man of Steel (2013) a dying industrial world with flying beasts, and James Gunn's Superman (2025) mostly left it off screen.

The destruction has always been the same story with a different cause. Jor-El discovers that Krypton is about to die, the Council refuses to believe him or to evacuate, and he and his wife Lara build one ship large enough for a child. The 1986 reboot by John Byrne made the cause a chain reaction in the planet's radioactive core; Man of Steel made it the Kryptonians' own core-harvesting, so that the planet dies of the people on it; the Phantom Zone criminals who survive the explosion, General Zod chief among them, survive because they were in prison. Krypton's fragments become kryptonite, the one substance that can kill its last son, first heard on the radio serial in 1943 and in the comics from 1949.

Superman in 1938 could not fly. He could leap an eighth of a mile, hurdle a twenty-storey building, outrun a train and shrug off anything short of a bursting shell, and the first page explained it by physics: Krypton's inhabitants had evolved to physical perfection on a planet of far greater gravity, so on Earth their strength was superhuman the way an ant's or a grasshopper's appears to be. Flight arrived in the 1940s cartoons because animating a leap was harder, heat vision and X-ray vision followed in the comics, and by the late 1950s the explanation had shifted from gravity to light: Krypton's sun was red, Earth's is yellow, and Kryptonian cells store yellow sunlight as power. A Kryptonian under a red sun is an ordinary person, which is how the comics turned the powers off when a story needed it.

The solar rule made the species a battery, and the writers have tested its limits ever since. Superman recharges by flying toward the sun; a blue sun gives more power; prolonged darkness weakens him; kryptonite radiation, the remains of his home, poisons the process; and gold kryptonite, in the older stories, removed the powers for good. Man of Steel added an atmosphere rule, so that Zod's soldiers in Kryptonian air and armour are weaker than Clark, who has breathed Earth's for thirty years. None of this is physics, but it is consistent, which is what a rule needs to be.

The species did not stay one person. Supergirl, Kara Zor-El, arrived in Action Comics #252 in 1959 as Superman's cousin, sent from a surviving fragment of Krypton, Argo City, that had drifted in space under a dome until its ground turned to kryptonite; her version of the origin, a teenager who remembers the planet, is the one the 2015 television series and the 2026 film used. The Phantom Zone, a ghostly dimension where Krypton imprisoned its criminals as disembodied projections, appeared in Adventure Comics #283 in 1961, and General Zod, its most famous inmate, in the same year; Terence Stamp's Zod in Superman II (1980) and Michael Shannon's in Man of Steel are the species' other face, the soldier who believes the last Kryptonians should rebuild Krypton on top of Earth.

Every survivor complicates the last-son premise, and the comics have added dozens: the bottled city of Kandor, shrunk by the villain Brainiac before the explosion; a clone; a dog named Krypto; a cousin's son; and, on television, whole colonies. The films have been stricter. Each cinematic reboot returns to one child, one ship, and the loneliness of the only member of a species, and each then gives him a Zod to show what the species would have been if it had survived intact.

Superman is a Nordic alien with a day job. The Nordics of contactee lore, tall, fair, physically perfect, morally superior human-looking beings from a more advanced world, are the Kryptonian as the 1950s reports described him, and George Adamski's 1952 account of a Venusian who looked like a handsome man in a ski suit could be a description of Clark Kent without the glasses. The comics came first by fourteen years, and the resemblance is unlikely to be an accident: Siegel and Shuster drew on the pulp supermen of the 1930s, the contactees grew up reading the same pulps, and both produced the same figure, a visitor who is better than us and here to help.

The other image the story shares with the lore is the crash. A small craft from another world comes down in a farmer's field, a rural family finds it, and the government, in most tellings, would very much like to know what was inside; that is the Kents in Kansas and it is Roswell, whose 1947 debris field was on a ranch and whose alleged bodies were small. The Kansas farm was in the strip from the 1940s, seven years before Roswell, and there is no evidence the Roswell story borrowed it; the two are the same wish, that what falls from the sky might be a child rather than a weapon. Whether a planet like Krypton could exist around a red star is a question the habitable exoplanets article takes seriously: most of the galaxy's stars are red dwarfs, and most of the potentially habitable planets found so far orbit them.