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Named after the chemical element krypton, the planet was created by Jerry Siegel and Joe Shuster, and was first referred to in Action Comics #1 (June 1938); the planet was given its first full-fledged appearance in Superman #1 (1939).
Krypton exploded as a result of a thermonuclear chain reaction deep within the planet's unstable Uranium core. As originally depicted, all the civilizations and races of Krypton perished in the explosion, except for one survivor: the baby Kal-L (later respelled as Kal-El) who was placed in an escape rocket by his father, Jor-L (Jor-El), and sent to the planet Earth, where he grew up to become Superman.
In some versions of the Superman mythos, additional survivors were later discovered, such as Krypto the Superdog, Supergirl, her parents (kept alive in the "Survival Zone", a similar parallel "dimension" to the Phantom Zone), the criminal inhabitants of the Phantom Zone, Dev-Em, Beppo the Super-Monkey, and the residents of the bottle city of Kandor.
From the late 1980's through the early 2000's, the number of survivors was greatly reduced in the comic book stories, but more recent accounts have restored Supergirl, Krypto, and Kandor, and introduced another newly discovered survivor, Karsta War-Ul.
The planet was called Krypton most likely because of its Greek root (κρυπτόν krypton, meaning "hidden thing" or "hidden one").
Versions of Krypton
Golden Age Krypton
In its first appearance, Krypton was only depicted at the moment of its destruction, details of life there being unaddressed and frankly irrelevant to Superman's adventures on contemporary Earth; the plain fact of his extra-terrestrial origin was considered sufficient enough to explain his superpowered status. Soon, beginning in the Superman comic strip, Krypton was shown to have been an evolved planet similar to Earth, older by eons and possessed of all the beneficial progress that implied (though the downside was the hint that Krypton exploded due mainly to old age). This can be seen in the early descriptions of Superman having come from "a race of super-men" in early comics and serials, and one of the labels associated with him, "The Man of Tomorrow".
Kryptonians, though otherwise completely human, were superior both intellectually and physically to natives of Earth. They lived under the rulership of a scientific elite, in cities of delicate art-deco towers, and wore costumes in the style of Alex Raymond characters. The trappings of Krypton were all rather reminiscent of the final technological utopia depicted in the H.G. Wells film Things to Come.
The debut of the Superman comic strip in 1939 also delved into further details about Krypton, including introducing the idea that all Kryptonians possessed a minimal level of heightened physical abilities, including super-strength and super-speed. In the early comics' version of Krypton, Superman's parents were named "Jor-L" and "Lora" (changed to the more familiar "Jor-El" and "Lara" by the end of the 1940s).
The Golden Age Krypton would be revised into another form almost as soon as it was defined (see Krypton in Transition below), and very few stories were written about it. However, after the introduction of DC's multiverse in the 1960s, this version of Krypton was declared to be the Krypton of the Earth-Two universe (the native dimension of DC's Golden Age characters) and its Superman. This was especially so in the late-1970s run of All Star Comics, where Power Girl, the Earth-Two version of Supergirl, was introduced.
In the Golden Age, Superman was unaware initially of his true origins; in Superman #61, Superman discovered the existence of Krypton for the first time and learned of his Kryptonian heritage. He later encountered other survivors prior to Kara's arrival in the form of three criminals, U-Ban, Kizo and Mala, who were exiled by his father before Krypton's destruction.
Krypton in transition
Over the course of the 1940s and 1950s, various alterations and additions to the makeup of Krypton were made in the comics. Among them was explaining why the natives of Krypton perished if they had possessed super powers on their native world (as was the case in the earliest versions of Krypton outlined above, although this only became a problem once Superman—and by extension anyone from Krypton—was portrayed as increasingly powerful, able to withstand nuclear explosions, contrasted with his original power level in which a bursting mortar shell could penetrate his skin). Thus, it was explained by the early 1950s that Kryptonians were powerless on their own planet, and would only gain super powers within a lower gravity environment. This matched the correct theories being published that when man reaches the moon (a lighter gravity environment) he will be able to lift great weights and leap great distances. In the early 1960s, added to this was the need to be exposed to the rays of a yellow sun (versus Krypton's red sun, which was older and "cooler", or put out less energy) to gain super powers, with the yellow sun aspect soon gaining the much greater emphasis. Other changes to the concept of Krypton and its culture were introduced, many of which were stylistic.
Silver Age Krypton
By the late 1950s, Krypton played an increasingly larger role in various Superman stories, with greater amounts of details given to Krypton's makeup.
The Silver Age version of Krypton had a clear resemblance to the jet age consumerist utopia then common in popular visions of the future. Kryptonians made use of their advanced science to create a world where scientific inventions and research influenced much of daily life. Robots and computers were used for many tasks on Krypton, even for determining what career paths young boys and girls would take as they grew up. Scientific and technological research was highly valued on Krypton, with the ruling body of Krypton named the "Science Council."
Several stories featured characters traveling back in time to visit Krypton before its destruction; the most well known of these is probably the 1960 story "Superman's Return to Krypton", in which Superman is swept back in time to Krypton some years before its destruction. Powerless, he spends some time on the planet, where he meets his future parents-to-be and falls in love with a Kryptonian actress named Lyla Lerrol. A Superman "imaginary story" entitled "What If Krypton Had Not Exploded?" (reprinted in the trade paperback edition The Greatest Superman Stories Ever Told) gave more insight into Krypton's society.
Superman's Kryptonian heritage was a frequent factor in Silver Age Superman comic storylines, as he was fully aware of his origins from an early age. Superman would use this knowledge for such tasks as constructing robots or observing some of Krypton's traditions.
The terrain of this Krypton was bright and vivid, featuring such landmarks as the Scarlet Jungle, the Gold Volcano, and the Jewel Mountains. The Scarlet Jungle in particular contained many strange beasts and plants, such as a species of giant mole that could eat through metal.
There were two consecutive capital cities on Krypton: Kandor and Kryptonopolis. The city of Kandor was shrunk by the evil android Brainiac and taken away; Kryptonopolis became the new capital of Krypton. In his first encounter with Brainiac, Superman discovered the city of Kandor preserved in a bottle. He rescued it and took it to Earth with him, vowing to someday discover a way to return the city to normal size. In the late 1970s, Kandor was enlarged, and its inhabitants left Earth to settle on a new planet named Rokyn.
Krypton had two moons, but one of them - Wegthor - was accidentally destroyed by the criminally deviant Kryptonian scientist Jax-Ur when he was experimenting with a nuclear missile. The disaster killed 300 inhabitants of the moon, and because of this, Jax-Ur became the first criminal to be banished for a sentence of life imprisonment to the Phantom Zone, which had been discovered by Jor-El. This disaster also prompted the Science Council of Krypton to ban space flight completely, providing another explanation of why Krypton's civilization perished with the planet.
The Silver Age Superman was not alone in the survival of Krypton's destruction, being joined by his cousin Supergirl, the Phantom Zone criminals, Beppo the super-monkey, Krypto the Superdog, a juvenile delinquent named Dev-Em, and the entire population of the city of Kandor. When the planet exploded, one entire city of Krypton, Argo City, survived the cataclysm.
Argo City drifted through space on an asteroid-sized fragment of Krypton, which had been transformed into Kryptonite by the explosion. The super-advanced technology of its Kryptonian inhabitants gave the denizens of Argo City the ability to construct a life-sustaining dome that allowed them to survive for several years, in addition to building a lead shield that protected their city from the Kryptonite radiation of their asteroid. However, the protective shield was destroyed in a meteor storm, exposing the inhabitants to the deadly radiation. One sole survivor of Argo City, Kara Zor-El, was sent to Earth by her scientist father to live with her cousin Kal-El, who had become known as Superman. Kara adjusted to her new life on Earth and became known as Supergirl. It was later discovered that Supergirl's parents had survived in the Survival Zone, a parallel "dimension" similar to the Phantom Zone, from which she released them. When the bottle city of Kandor was finally enlarged on a new planet, Supergirl's parents joined its inhabitants to live there.
In 1979, a mini-series entitled World of Krypton was published, providing a great amount of detail into Krypton's history just before its destruction, along with the life story of Jor-El himself. A three-issue miniseries entitled The Krypton Chronicles, published in 1981, tells of Superman researching his roots when, as Clark Kent, he was assigned to write an article about Superman's family by an assignment editor impressed with the television miniseries Roots. To do so, he and Supergirl travel to Kandor where they learn the history of the El family. In 1985, writer Alan Moore gave a somewhat darker glimpse into the world of Krypton in his story "For the Man Who Has Everything" (in Superman Annual #11), the premise being an elaborate dream of Superman's in which Krypton had not exploded and he'd grown to adulthood there. Background details are culled from other Krypton stories. This same story was retold in the animated series Justice League Unlimited in an episode by the same name.
The people now known as Daxamites were originally Kryptonians who left their homeworld in order to explore the Universe. The Eradicator, an artificial life form programmed to preserve all Kryptonian culture, altered the birthing matrices ("artificial wombs") that the explorers took with them so that all newborns would be fatally vulnerable to lead and other materials such as greenhouse gases and certian rocks. Thus, if they persisted in their anti-Kryptonian wanderlust, they would all die from it. One Daxamite, Mon-El, was poisoned by lead, and preserved in the Phantom Zone until a cure was found by Brainiac 5 in the 30th century, whereafter Mon-El became a member of the Legion of Super-Heroes.
Crisis on Infinite Earths
After the 1985 mini-series Crisis on Infinite Earths, this version of Krypton was soon replaced by a newer version. However, the Silver Age Krypton made a rare post-Crisis appearance in The Sandman #48, during a flashback sequence featuring Death and Destruction of The Endless, beings who were evidently unaffected by the reality-altering events of the Crisis. In the relaunch of the Superman franchise, it was declared that the new version would never encounter another surviving Kryptonian.
The Man of Steel
Following Crisis on Infinite Earths, which rebooted the history of the DC Universe and retro-actively eliminated the existence of the Golden and Silver Age versions of Krypton, writer/artist John Byrne was given the task of recreating the entire Superman mythos. This rewrite was started in the 1986 Man of Steel miniseries, which addressed Krypton in both its opening and closing chapters.
Krypton itself was the main subject of the late 1980s The World of Krypton miniseries (not to be confused with the 1979 mini-series of the same name). This mini-series was written by Byrne and illustrated by Mike Mignola, and filled in much of Krypton's new history.
The new Krypton was approximately the size of Earth and orbited a red sun called Rao, 50 light-years from our solar system. Over 100,000 years ago, Krypton had already developed scientific advancements far beyond those of present-day Earth, and by a few millennia past had conquered disease, learned to retard the aging process, and perfected cloning; vast banks of non-sentient clones held multiple copies of each living Kryptonian so that replacement parts were always available in the case of injury. All Kryptonians were effectively immortal and eternally young, and enjoyed an idyllic, sensual existence in an Arcadian paradise.
However, this society was tipping towards decadence and eventually political strife which resulted from the debate as to whether clones should have rights (sparked by the presence of an alien missionary known as the Cleric). Eventually this disagreement led to open violent conflict especially after it was openly discovered that a woman's cloned copy of herself was allowed to gain full sentience and to establish a full, normal life. However, when a young man (the original woman's son) had discovered that his wife was this clone, he killed the clone (presumably), and then publicly killed his mother, and also attempted his own suicide. This key incident (see the Post-Crisis mini-series World of Krypton) ignited the Clone Wars, during which Kryptonian science was turned to warfare and several super-weapons were developed and used. Among them were the devices which became known as the Eradicator and the Destroyer.
Although the Eradicator's effects (altering the DNA of all Kryptonian life-forms so that they would instantly die upon leaving the planet) were felt immediately, the Destroyer's effects were possibly more significant: by the time the Kryptonian government admitted defeat and abolished the clone banks, a pro-clone rights terrorist faction known as Black Zero had started the Destroyer, a device which functioned as a giant nuclear gun, projecting massive streams of nuclear energy into the core of Krypton, intended to trigger an explosive chain reaction within Krypton's core almost immediately.
At the time, it was believed that the device had been stopped before it could achieve this (ironically, by an ancestor of Jor-El himself), but eventually it would be discovered, centuries later by Jor-El, that the reaction had only been slowed to a nearly imperceptible rate and would eventually destroy the planet as intended. Also, the destruction of the Destroyer resulted in a nuclear explosion which eliminated the post-crisis city of Kandor.
The Destruction of Krypton
In the meantime, though it had for now survived the war, Krypton was scarred deeply by it. The formerly lush garden world was burned and blasted, left mostly a lifeless desert. In direct contrast to the society that had existed prior to the Clone Wars, a sterile, emotionally dead civilization emerged. The population became isolated from one another, living in widely separated technological citadels and shunning all personal, physical contact. Procreation would then become a matter of selecting compatible genetic material which would then be placed within an artificial womb called a "birthing matrix." Any attempt to contact other worlds was forbidden, and the planetary government maintained an isolationist stance, forbidding space exploration of any kind.
It was into this world that the young scientist Jor-El was born. By his adult years, the mysterious "Green Plague" was killing Kryptonians by the hundreds, and upon researching the matter, Jor-El discovered that the cause was growing radiation produced by Krypton's increasingly unstable core. Due to this process, the entire planet itself was going to explode.
Unable to convince his associates to abandon tradition and consider escape, and reasoning that modern Kryptonian society had grown cold, unfeeling and thus decadent Jor-El took the birthing matrix of his unborn son Kal-El, removed the Eradicator's planetary binding, and attached a prototype interstellar propulsion system to the vessel. Just as the planet began to shake apart, he launched the matrix towards Earth, where it would open and give birth to the infant upon landing (the post-Crisis Superman therefore was technically "born" on Earth). Jor-El was not only determined that his son would survive the death of his birthworld, but that he would grow up on a world that vibrantly embraced living, as his pre-Clone Wars forbears once did.
The Last Son of Krypton
A central theme of this version of the Superman mythos was that the character was to remain the last surviving remnant of Krypton. Thus, Silver Age elements such as Supergirl, Krypto, and Kandor had never existed in this version (though post-Crisis versions of these elements were eventually reintroduced).
The super-villain Doomsday was revealed in the 1990s as a being genetically engineered by Bertron, an alien scientist, on an ancient Krypton; this happened hundreds of thousands of years before the rise of Krypton's civilization (this fact explains how Kryptonians obtained their advanced technology.
In the newer continuity, Superman also only became aware of his alien heritage sometime after his debut as a super-hero, when a holographic program encoded into the craft which brought him to Earth uploaded the information into his brain.
In a late 1980s storyline, Superman traveled to the former site of Krypton to discover that the planet was slowly reforming from the vast sphere of debris remaining. However, it would take millions of years before the planet would be solid again. This sphere of debris had been turned to Kryptonite by the planet's destruction, and the radiation causes Superman to have a hallucination concerning an alternate scenario in which the entire population of Krypton comes to Earth.
In the 1990s comic series Starman, Jack Knight became lost in time and space, landed on Krypton several years before its destruction, and met Jor-El as a young man. The story boldly implies that it was this early meeting with a Terran that led Jor-El to study other worlds, and eventually choose Earth as the target for his son's spacecraft.
In an early 2000s storyline, an artificial version of the pre-Crisis Krypton was created in the Phantom Zone by Brainiac-13, a descendant of the original Brainiac who had traveled back in time to the present. It was stated to have been based on Jor-El's favorite Kryptonian historical period.
In the 2004 mini-series Superman: Birthright, a new retelling of Superman's origin and early years, Mark Waid depicted a Krypton, officially stated as being located in the Andromeda Galaxy 2.5 million light-years away, with elements of various versions of the planet, but closer to the pre-Crisis version. It was later implied that the time-bending adventure in Superman vol. 2, #200 and events in Infinite Crisis had re-written history so this was now the "official" version, and later stories have held Birthright as being the official current version of Superman's origin.
Waid also made use of Superman's "S"-shield in his version of Krypton. While in previous comic versions of the mythos, it was assumed the "S" simply stood for "Superman"; in Birthright, Waid presented the symbol as a Kryptonian symbol of hope (borrowing and modifying a concept from Superman: The Movie, where the "S" represented the House of El). DC's mandate for Superman being Krypton's only survivor changed as well. Birthright heralded the return of Krypto, Kandor, and Kara Zor-El as Supergirl. Superboy's origins were later retconned so that he was now the cloned son of Superman and Lex Luthor, making him half-Kryptonian.
However, a current storyline co-written by Geoff Johns and Superman director Richard Donner presents yet another version of Krypton which reintroduces General Zod and the Phantom Zone criminals into mainstream continuity. With art by Adam Kubert, the design of Kryptonian society is distinct yet again from Birthright, incorporating elements of both pre-Crisis on Infinite Earths continuity and Donner's work on the first two Christopher Reeve films, in particular the notion of Krypton's Council threatening Jor-El with harsh punishment were he to make public his predictions of their planet's imminent doom. Whether this further revision of continuity has an in-universe rationale is as yet unknown, but it may stem from continuity changes wrought by the reality-fracturing conclusion of Infinite Crisis.
Krypton in other media
The first non-comics version of Krypton was presented in the debut storyline of the 1940s Superman radio series. In the radio show, Krypton was part of our Solar System, a Counter-Earth sharing Earth's orbit but on the opposite side of the Sun.
- Krypton was very briefly depicted in the first Fleischer Studios-produced Superman cartoon in the early 1940s as "a planet that burned like a green star in the distant heavens [and where] civilization was far advanced and it brought forth a race of Supermen whose mental and physical powers were developed to the absolute peak of human perfection", implying that all Kryptonians had Superman's abilities even on their own planet. The planet is seen only from a distance.
- Depictions of Krypton on both The New Adventures of Superman and Super Friends are generally similar to those of the pre-Crisis comic books.
- In Superman: The Animated Series, "The Last Son of Krypton", the first part of a three-part pilot episode, depicts Krypton as being basically similar to the pre-Crisis version (it was scientifically advanced, Kal-El appeared to be about two-years-old as in the Silver Age comics, there are depictions of peculiar animals) although with elements of the John Byrne version (such as the appearance of the characters' wardrobe). Krypton's climate is shown to have both temperate and Arctic conditions. According to commentary on the DVD collection for the show's first season, part of Krypton's appearance was influenced by the artistic style of American comic book artist Jack Kirby.
- This version depicted the villain Brainiac as responsible for the destruction of Krypton's people. Brainiac as well as Jor-El discovered that the planet would explode after several weeks of earthquakes. Brainiac knew that if the Kryptonian elders learned of it, Brainiac it would be tasked with formulating an evacuation plan. This would leave Brainiac with no time to escape itself, so it told the elders that Jor-El was mistaken and that the earthquakes were the result of a polar shift and secretly downloaded itself and all of Krypton's culture and knowledge onto a satellite.
- Krypton had a "sister planet" named Argo, colonized by people of Kryptonian descent. On a journey into space, Superman found that the explosion of Krypton pushed the planet from its orbit away from its sun, making the planet gradually become colder. Its people went into cryostasis to survive, but an accident left Supergirl the only survivor.
- In the Legion of Super Heroes animated series, Krypton is shown in a flashback during the episode "Message in a Bottle." Here, Jor-El actually managed to find a way to save the planet with his creation, the crystal-creating "Messenger." The Messenger was kept in the city of Kandor, until the city was shrunk and stolen by Brainiac, causing the planet's destruction. At the end of the episode, the Messenger is used to restore Krypton from its remains, and Kandor is restored to its full size so its people can begin life anew.
Superman: The Movie
With the release of the first feature-length Superman movie in 1978, a vastly less idyllic image of Krypton, compared to the previous comics' versions, was presented. Whereas in the comics, Krypton was colorful and bright, in Superman, the planet was envisioned as having stark white terrain of jagged frozen plateaus, stretching broadly under heavy, dark skies.
Kryptonians themselves were portrayed as being a coolly cerebral society, clad in stark white body-suits eblazoned with the standard of each family's house symbol, and treading through halls of antiseptic, white crystal under crystalline arches. The crystalline motif was employed not only in the architecture, but in the landscape and technology as well, suggesting that the entire planet had been adapted and altered by Kryptonian influence. Krypton was ultimately destroyed when its red sun began to collapse; the planet was pulled into the sun and steadily crushed, then exploded when the star went nova.
This version of Krypton was to have a strong influence on John Byrne's 1986 re-imagining of the world. However, the film's Krypton was still presented as having a society "better" than Earth's, unlike the Krypton that Byrne envisioned. For example, there was no death penalty on Krypton because almost all criminals were rehabilitated (the ones that were not or were beyond rehabilitation such as General Zod were banished to the Phantom Zone). Superman himself thought very highly of the planet and was proud to have come from there. Also, in this version of the story, both Jor-El and Lara preserve some part of their essence in the starship that brings their child to Earth, so that on Clark Kent's eighteenth birthday, Jor-El appears to him within the Fortress of Solitude and initiates twelve years of Kryptonian education for the youth, and both remain as constructs within the Fortress until it is ransacked by Lex Luthor (see below).
The origin of Superman's symbol is given a Kryptonian origin in the film (as Mark Waid's Superman: Birthright would years later). Male Kryptonians are shown wearing unique symbols on the chests of their robes, similar to a family crest; Jor-El and Kal-El after him wear the familiar S-shield, which Lois Lane later assumes to be the letter 'S' from the familiar Latin alphabet, and thus dubs him 'Superman'.
The idea for Jor-El to have the symbol was suggested by actor Marlon Brando, who portrayed Jor-El in the movie, and eventually was retconned into the comics continuity as being the crest of the House of El, which both Superman and Kara Zor-El are part of. In more recent years it has been adapted by comics writers to be an actual letter/glyph in the Kryptonian alphabet, with the standard version of the shield meaning 'hope', and the inverted (upside-down) version meaning 'resurrection'.
In the pilot episode of the 1950's television program Adventures of Superman Jor-El, portrayed by Robert Rockwell, was Krypton's leading scientist, who tried to warn the ruling council of Krypton's demise. Krypton is barren in color similar to that of Superman. Jor-El also wore a white robe with the S on his chest similar to that of his son.
The version of Krypton used on Lois & Clark: The New Adventures of Superman was somewhat similar to the version in Superman. Though they possessed highly advanced technology, this version's Kryptonians were more loving than John Byrne's Man of Steel version.
The 2006 movie Superman Returns presents a version of Krypton almost identical to Superman (since Superman Returns is more or less set in the same continuity as Superman). In the beginning of the film, scientists discover remains of Krypton, and Superman leaves Earth for five years to look for it. His ship is seen leaving the dead planet. In the shooting script for the film (under the production title "Red Son"), Lex Luthor reveals to a weakened Superman that his henchman actually set Superman up to believe that Krypton still existed by sending false signals.
During the beginning, we see the city where Kal-El was born (including the famous white dome that housed the trial of General Zod, Ursa, and Non), then as to replicate the lift-off, other cities can be seen on the night side and then finally the planet's destruction by a supernova of its red supergiant sun.
Superman Returns extends the crystalline Kryptonian technology from Superman which allowed young Clark Kent to "grow" the Fortress of Solitude. In the new movie, Kryptonian crystals are able to grow huge land masses and incorporate the properties of the surrounding environment; a sliver taken from of one of the crystals used to test the theory causes Lex Luthor's basement to be filled with a huge crystal structure. Growing land in this manner causes widespread power failure in the vicinity, inadvertently causing the emergency involving a space-shuttle and an air-liner which acts as Superman's triumphant return. When he later returns to the Fortress of Solitude to find that the crystals that powered it have been stolen, Superman is visibly enraged. Lex Luthor later combines one of the crystals with kryptonite and shoots it into the ocean, creating what he calls "New Krypton". After being stabbed and falling into the sea, Superman uses his heat vision to get under the crust of the island and he then throws it into space, nearly killing himself in the process. Bryan Singer has stated that the "New Krypton" island may return in the sequel.
The novelization by Marv Wolfman further expands on the "S" as well, stating that one of Superman's ancestors helped civilize Krypton long ago, and the crest was considered one of the three most respected icons in Kryptonian culture.
Novelist Kevin J. Anderson presents the last days before Krypton's destruction in the novel The Last Days of Krypton. It is a sweeping tale of the pomp and grandeur, the intrigue and passion, and the politics and betrayals of a doomed world filled with brave heroes and cruel traitors. Depictions of the planet's society and culture loosely resemble elements from the motion picture Superman, television series Smallville, and the post-Infinite Crisis interpretations.
Last Son of Krypton
The 1978 novel Last Son of Krypton by Elliot S! Maggin contains descriptions of Krypton, mainly referencing the Silver Age version; it describes the planet as a "failed star" with massive surface gravity and extremenly hostile, glaciated conditions, which forced extreme adaptation and rapid evolution in the descendants of humanoid space travelers (and their dogs) who became stranded on its surface in prehistory. This led to an extremely strong, dense, and durable Kryptonian species with unusual physical properties. Maggin describes the rise of a civilization which uses geothermal heat as its primary power source, developing science and technology, but finding it difficult to escape the massive world's gravity. Eventually its internal nuclear reactions led to Krypton's explosion.
- In issue #22 of Futurama Comics, in the last panels, Jor-El is seen warning the science council that Krypton is about to explode. The reason they ignore him is because their "Bender-brand Planetary Destruction Detector" would let them know an hour in advance. It goes off one minute after the planet blows up.
- In April, 2007, astronomers in Switzerland, France, and Portugal announced that they had found an Earth-like planet orbiting in the habitable zone around the red star Gliese 581. This planet, larger than Earth, is said to have a mass more than 5 times that of Earth, which would mean a commensurate increase in gravity. It is notable that the announcement of the discovery of this planet, which resembles early descriptions of Krypton, comes within days of the announcement of the discovery of a substance matching the characteristics of Kryptonite.'Kryptonite' discovered in mine
- In the 2007 game, Sam and Max Season One :the fourth episode "Abe Lincoln Must Die"; Max mentions to destroy Krypton with a missile homing beacon at the White House's Presidential War Room after being sent to the Phantom Zone. After deploying the missile, the screen reads "reaches in 26 million years", and Max says "Aw"
- Superman: Birthright
- Krypton Glossary
- Fictional planets
- Vathlo Island
- Supermanica: Krypton Supermanica entry on the pre-Crisis Krypton
- Superman: Fathers Coverage of the version of Krypton shown in Superman (volume 2) #166
- Excerpt of Superman: Birthright Superman re-imagined for the 21st century!
- Alan Kistler's Profile On: SUPERMAN - Comic book historian Alan Kistler gives a detailed analysis of Superman over the decades, as well as the different interpretations of the planet Krypton and how Kryptonians acted.