Baby Planet

An inhabitable planet that is far smaller than astronomically possible, often less than a few functional miles in diameter. As a general rule, a Baby Planet is small enough that you can see its curvature even on the surface. In Real Life, a body this small would be called an asteroid, and would be incapable of supporting an atmosphere (of useful density at a life-supporting temperature), and would probably not even be spherical, but in fiction, these often sport an entire ecosystem awkwardly compressed into the minute available space.

Although Sci-Fi Writers Have No Sense of Scale, they usually aren't this far off the mark on accident; this trope usually comes about either because of limitations in technology's ability to represent planets in a realistic scale, or just for the sake of aesthetic.

Often, this is used for purely aesthetic reasons, particularly on cover art for games and CDs. Just as often it's Art Major Physics. In photography, this effect is often created with very-wide angle (or fisheye) lenses.

Bonus points if it's unusually shaped too.

Related to Floating Continent. Not to be confused with LittleBigPlanet, It's a Small World After All or Planetville.


  • In the UK, British Gas have been running a series of rather fun adverts based on the idea that "your home is your world"; the person whose boiler is up the plonk lives on a tiny planet that is their house, drive and garden!! And their cars and vans take them to other planets and some planets have theme parks... sounds like a cross between The Sims and Super Mario Galaxy in advert form. Some of them are gathered here.

Anime and Manga
  • King Kai's planet in Dragon Ball Z. Despite being maybe fifty feet in diameter, it strangely has ten times earth's gravity. Based on King Kai's vague explanation, it apparently has the same mass as Earth, heavily compressed. This should technically make it a neutron star, but then, nobody ever accused Dragon Ball Z of realism. Even if they did, it's still the self-built home of a Physical God, and still set up in a corner of the afterlife, so it might as well be decorated with "A Wizard Did It" in 50-foot-high neon any way the audience looks at it.
  • An episode of Sgt. Frog had one of Keroro's last-ditch invasion schemes involve stealing garbage and water from Earth to create a mini-planet. We learn it was a "last-ditch" scheme because unauthorized planet creation is against the law, and when the planet creation goes out of control it nearly becomes big enough to qualify as a full planet, leading to the Keronians nearly getting arrested by Space Police officer Poyon.
  • In Oyasumi Punpun, Punpun dreams up a small meteor that fits the bill, which he names Punpunia. It's really only big enough for his house, family, and a few stray animals.

Comic Books
  • A Silver Age Superboy story had Clark Kent travel to a small asteroid/planet, where he found someone with powers similar to his own. At the time, the preferred explanation for Superman's powers was that Krypton was larger than Earth, so the native race evolved to counteract the more powerful gravity. The boy on the asteroid, it turned out, was from Earth, so on his little world he got to have some of the same benefits Superboy did. The native races of all 3 ecosystems evolved to be identical in size and shape. . .
  • Carl Barks' Uncle Scrooge comic "Island in the Sky" features a couple of asteroids that are somehow capable of supporting life. They also orbit each other closely enough to share an atmosphere.
  • The Dutch comic Storm has this as a common sight in the solar system the later albums are set in.

  • The CGI shots of the Earth in Zombieland (which are apparently the mental images of the narrator).
  • The movie Timelock is set on a prison asteroid. It is at least established to be very cold outside (and the worst offenders are hung outside in a state of suspended animation). Then the movie goes and violates its own logic at the end, when Riley sticks three small nuclear devices on Villum and knocks him into an abyss. Villum is shown alive and well in the very last minute of the movie.

  • "Asteroid B-612" from Antoine de Saint-Exupery's The Little Prince may be the Trope Codifier, if not the Trope Maker. It's house-sized, which makes it bigger than most neighboring planets. And he keeps encountering new stuff on it every day, including baobab trees.
  • Justified in Larry Niven's Protector due to use of gravity generators, etc.
  • Played straight and justified in the novel The Collapsium by Wil McCarthy: one of the main characters lives on an artificially constructed planet which is only a few hundred kilometers wide. It has a core made out of degenerate matter in the form of neutronium which gives it Earth-normal gravity, holds it in a spherical shape and allows it to retain an atmosphere.
  • The Mushroom Planet in the eponymous novels.
  • The Frederic Brown story Placet is a Crazy Place features a tiny planet with a breathable atmosphere with a core made of extra-dense 'heavy' matter to give it its shape and gravity. It even has life forms made of heavy matter that "fly" through the crust (which is like air to them since they are so dense), causing earthquakes. It obviously suffers from the "what keeps the heavy matter from expanding" problem, but might be excused since it is a story from the 40s and Science Marches On. Also, the heavy matter "birds" that cause earthquakes are completely 100% excused by the Rule of Funny; the buildings on Placet are small and light, and never last more then three weeks. The birds fly right through the foundations. Also, Jack Vance's short story "We'll Build Your Dream Castle" retreats for the super-rich are built on a few dozen chunks of super-dense matter in orbit near Earth.
  • Gary Gibson's Stealing Light has at least one asteroid fitted with a Shoal 'world engine', and their Coreships.
  • In The Light Fantastic, the great world turtle Great A'Tuin ushers eight eggs into the world, each hatching to reveal a perfectly formed baby turtle, each supporting on its back a group of elephant calves which on their back support a proto-Discworld. These then swim from the shores of harsh reality back into the depths of the improbable part of the universe that supports such things.
  • The backstory of House of Suns features a planetoid that held the Gentian household in the distant past. It had standard Earth gravity which was hinted to be due to a small black hole contained within the planetoid.

Live-Action TV
  • Several episodes of The Twilight Zone TOS had asteroids with normal Earth gravity and a breathable atmosphere.
    • Played straight in "The Lonely"
    • Lampshaded in "Elegy". The astronauts specifically mention that an asteroid shouldn't have Earth gravity and atmosphere.
    • Subverted in "I Shot An Arrow Into The Air". Some shipwrecked astronauts think they're on such an asteroid: they're actually on Earth!
  • Lexx:
    • Season 2 had something like this, a small planetoid with an artificial atmosphere that was a TV studio center. Our 'heroes' wind up there and find that if their ratings slide they'll be in trouble.
    • In one episode, a planetoid was so small you could see grazing sheep on its surface from orbit. For unexplained reasons, it had Earthlike gravity.
  • Aversion: In the original Star Trek episode "That Which Survives" the fact that a Luna-sized world has Earthlike atmosphere is one of the clues that something's amiss.
  • The official atlas for the Firefly verse says even the small moons, barely large enough to be balls (think Mimas or Enceladus), are terraformed using gravitic technology.
  • Justified with a Baby Universe in The New World of Mr. Tompkins. The gravitational constant is enormous.
    • Inverted in Relativity Land- Relativity Land should be a black hole if gravity still works the same despite the speed of light being 30 mph or less.

  • Album cover art: The miniature planet on the cover of Fragile by Yes. (On the back cover, the planet breaks up and the population escape in a wooden space glider. This later inspired Jon Anderson's solo album Olias of Sunhillow.)

Video Games
  • Spore. The planets look regular-sized from close, but appear increasingly tiny as you advance towards the Space Stage. To give you an idea of scale: You can find Earth. The UK is about the size of an average spaceship.
  • Kingdom Hearts. One of the unique artistic features in the first game was condensing of most of the Disney worlds into miniature planets, most of which could be seen from 'space'. The worlds themselves, while modeled after the various Disney worlds, tend to be as small as possible, no more than a few miles each. The residents don't seem to notice.
  • Super Mario Galaxy not only has baby planets; it has baby galaxies. As in, galaxies that're not much bigger than a large paddock.
  • The Prince Planet in Katamari Damacy (very obviously based on The Little Prince's,) as well as Earth itself if you get big enough to notice the curvature.
  • The cover of Animal Crossing: Wild World, and in addition, in-game the ground curves downward into the distance.
  • The freeware game Frozzd features dozens of such planets.
  • The American cover art for Bullfrog's Theme Park game.
  • In Yoshi's Island, you fight Raphael the Raven on one of these. To be clear, it is the world's moon.
  • Spacebuild maps for Garry's Mod have very small planets generally no bigger than about the size of a football field, though largely due to the Source engine's max map size capping out under 1 kilometer^3.
  • The Tiny Bang Story.
  • Albion. The titular planet is considerably smaller than Earth, but is mostly made up of exceptionally heavy metal, making the planet's mass just slightly smaller than Earth's.
  • Angry Birds Space features many levels with small planetoids that have gravity bubbles that affect the birds' trajectories.
  • Planets in Planetary Annihilation range between this and more reasonable sizes, depending on the settings used. Nevertheless, they're much closer than would really be possible, in order that interplanetary travel doesn't take ages.
  • Incoboto Mini has the main character running across several small planets as part of the gameplay.
  • One of your party members in Anachronox is an entire miniaturized planet, Democratus.
  • The planet Auraxis in PlanetSide 1 has a tiny surface area, less than 1000 km^2, along with a thin atmosphere which cannot sustain air-breathing engines past 400m above sea level. Being heavily infused with Ancient Vanu technology, it has been theorized that the planet has a black hole in its core to provide gravity. The sequel has the same issue of tiny scale - in fact, it's even smaller - but almost triples the flight ceiling.
  • In Sonic Adventure 2, Rouge has a large stage called Mad Space, which features tiny planetoids similar to those later seen in the Super Mario Galaxy series. They pull Rouge into their gravitational field if she jump or glides too close. One of them is cylindrical in shape.
  • This is downplayed in Rodina. The asteroids are too small to support atmospheres, but they do have enough gravity for you to walk on without floating into space.

Web Animation

Web Comics
  • In The Inexplicable Adventures of Bob!, the planetoid of Fleen follows this trope, even to the point of depicting The Little Prince's asteroid floating nearby.
  • Prospit and Derse from Homestuck: If the size of the towers on their respective moons is any indication, they are smaller than a Death Star, though still quite big. This ultimately applies to almost every planet in the Incipisphere; the players' Lands are likely less than a hundred kilometers in diameter, small enough that at a fairly distant view the players' homes are still visible, giant tower status notwithstanding. Skaia and The Battlefield within it are large, but still fairly small for a planet.

Web Original
  • Discussed on this issue of the What If? Blog, mostly with regard to what the gravitational effects of such a world would be, if it could exist.

Western Animation
  • Futurama:
    • Briefly alluded to in an episode where a planet implodes, leaving behind something the size of a large boulder with a few of its native animals pathetically hanging on. As far as the cast is concerned, this is an acceptable level of survival for them.
    • "The Mutants Are Revolting" with Mrs. Astor's asteroid. Has both an atmosphere and normal gravity.
    • Inverted when the Sun seems to have Earth gravity...and is a lava planet.
    • One episode has Fry remarking on how small entire planets can appear when you're flying through space, at which point a Saturn-like planet that appeared to be off in the distance is revealed to actually be about the size of a large bug when it hits the ship's windshield like one.
  • The Clangers' The Clanger Planet. It has vaguely moonlike craters, and in one episode a Lunar Module lands and an astronaut plants a flag (which the Clangers adopt as a tablecloth,) but it's referred to by the narrator as a "star" and exists among other similar worldlets. But since the Clangers occasionally leave it for the space above without any breathing problems, it runs strictly on Cartoon Physics.
  • The Transformers Generation 1 portrayal of Cybertron. Curvature could often be seen, and buildings could be seen from space. When Cybertron was moved into Earth's orbit, it was shown to be smaller than the moon - close enough for a plane-bot to fly to in under a minute, and yet the entire planet could be easily seen whenever it was in frame. Asteroid-sized is generous, and yet it's shown to have gravity comparable to Earth.
  • In Duck Dodgers in the 24½th Century, Planet X gets reduced down to a rock that's barely large enough for Dodgers and Marvin the Martian to both stand on. Nonetheless, it still has air, and some weird kind of gravity that allows someone to fall off.
    Duck Dodgers: As I was saying, buster, this planet ain't big enough for the two of us, so off you go! (pushes Marvin off) Now, this planet is hereby claimed in the name of Earth by Duck Dodgers in the Twenty-Fourth-and-a-Half Century!
    Cadet: A-a-a-a-big deal.
  • All the planets in Tiny Planets.
  • All the planets in Wander over Yonder are small enough for buildings, mountains, and other features around that size area to be visible from space.

Real Life
  • Theoretically, you could have things like this. They just would have to be on the larger end of this scale (or be very deep), and have constant support (artificial atmosphere, seeding life, etc). There's no real idea how this would work in practice, but there's decent ideas that it could work.
    • One way that probably wouldn't work would be compacting a large planet to a smaller size. The escape velocity of an object depends on how compact it is; that is, the ratio of its mass to radius. So the more you compact a planet, the higher the surface gravity would be - the Earth itself compacted to 3 miles across wouldn't be a black hole, but we certainly wouldn't suggest walking around on it.
    • Baby Planets might be able to be constructed once Magrathean construction technology is attained, by creating a world around a superdense core. Considerably less mass than the Earth would be required given the distance from the surface to the gravitational center would be significantly less, so long as the gravitational pull of the core was not enough to decompose the shell of nuclear matter around it, and as long as the diameter is large enough that tidal forces (difference in gravity between feet and head) don't cause serious trouble. Except neutronium is unstable in piles less than 1/10 of a solar mass due to the fact that neutrons are more massive than protons. Anything lighter than 1/10 of a solar mass and made of nuclear matter will decay, then explode as the electrical repulsion overcomes gravity.
    • A black hole inside a hollow shell could work (this is used in The World is Round, a novel by physicist Tony Rothmann, though in this case the planet in question is much larger than Earth, and the scheme is used to keep the surface gravity down). Black holes less than about the mass of the Moon are theoretically thermodynamically unstable, though this is much less of a problem than with neutronium (they would eventually evaporate, but it turns out the lifetime for a black hole of mass 10^11 kg ... roughly the mass of a hill of dry sand 250 m high ... is in the billions of years, with larger holes having even longer lifetimes).
  • Icy moons, such as Europa and Enceladus, are theorized to be capable of housing aquatic life and ecosystems. Europa is a bit smaller than earths moon, and Enceladus is about the size of the British Isles. However, as small on the scale of celestial bodies they are, they are still much larger than a true Baby Planet.
  • Polar panorama photos look very much like tiny planets and can be made from any panorama photo, such as a cityscape.