9 Types of Planets

How far a planet is from its star and what it's made of can give it a completely different face. Let's explore the 9 planet types you'll meet in Planetica, with real examples from space.

What makes planets different?

Two main factors shape what a planet looks like. One is the heat it gets from its star, which depends on the star's brightness and the planet's orbital distance. The other is the planet's size and what it's made of. Small planets are mostly rock and metal, while big ones wrap themselves in thick layers of gas. Even among rocky planets, depending on the heat they receive and their atmosphere, some have rolling oceans while others turn into deserts or are covered in ice.

Temperate world

A temperate world is a rocky planet like Earth, with liquid water on its surface and a mix of land, sea and clouds. This kind of environment forms when a planet sits in the habitable zone, neither too close to nor too far from its star, and has an atmosphere of just the right thickness.

So far, Earth is the only planet confirmed to meet all of these conditions. Several exoplanets have been found in habitable zones, but whether they actually have oceans and atmospheres hasn't been confirmed yet. In Planetica, you'll see continents, oceans, clouds and a blue atmospheric glow all together.

Ocean world

An ocean world is a planet whose surface is mostly or entirely covered by deep water. It's thought that a planet that formed far from its star with lots of ice could become one if it later moved inward and its ice melted.

The Solar System has no planet with an ocean surface, but Jupiter's moon Europa and Saturn's moon Enceladus are known to have oceans beneath their icy shells. The exoplanet GJ 1214 b was once considered a promising water-world candidate, but later observations revealed a thick atmosphere and haze, and its true nature is still debated. In Planetica, ocean worlds appear wrapped in seas that stretch to the horizon and in clouds.

Desert world

A desert world is a rocky planet with almost no water, covered in dry land. A planet ends up like this if it was a bit too close to its star and its water evaporated, if it had little water to begin with, or if it lost its atmosphere and its water escaped.

Mars is a great example of a cold, dry desert world in our Solar System. It still shows traces of past rivers and lakes, but today it's covered in red sand and rock under a thin atmosphere. In Planetica, wide stretches of ochre and red land cover most of the planet instead of oceans.

Ice world

An ice world is a planet so cold that its water is frozen solid. Ice worlds often form far from their stars, especially beyond the frost line, where water exists as ice.

In the Solar System, bodies like Pluto and Europa have icy surfaces. The exoplanet OGLE-2005-BLG-390Lb, a cold planet several times Earth's mass, is estimated to have a surface temperature of around -200°C, making it an ice-world candidate. In Planetica, you'll see white and bluish ice covering the whole planet.

Lava world

A lava world orbits so close to its star that its surface is hot enough to melt rock. Its dayside is thought to be covered by an ocean of molten lava. Planets like this are found on orbits so tight that they circle their star in a day or a few days.

Well-known examples include 55 Cancri e, which orbits a star in the constellation Cancer, along with CoRoT-7b and Kepler-10b. All are estimated to have surface temperatures well above 1,000°C. The Solar System has no lava worlds, but Jupiter's moon Io is still bursting with volcanic activity today. In Planetica, you'll mostly find them on scorching orbits very close to their star.

Gas giant

A gas giant is a huge planet made mostly of hydrogen and helium. It has no solid surface; its thick atmosphere just keeps going deeper and deeper. Gas giants are known to form when ice and rock clump together beyond the frost line into a large core, whose gravity then pulls in vast amounts of the surrounding gas.

Jupiter and Saturn are the Solar System's gas giants. Discovered in 1995, 51 Pegasi b was the first exoplanet found orbiting a Sun-like star: a hot Jupiter hugging its star and completing an orbit in just over 4 days. This discovery showed that gas giants can migrate inward after they form. In Planetica, they appear with banded atmospheres, often accompanied by rings or moons.

Ice giant

An ice giant is smaller than a gas giant but much bigger than Earth. Beneath a hydrogen and helium atmosphere it contains a lot of water, ammonia and methane. Astronomers call these substances “ices,” which is where the name comes from.

Uranus and Neptune are the Solar System's ice giants. Methane in their atmospheres absorbs red light, giving them a blue tint. Many Neptune-sized planets have been found around other stars too, including hot Neptunes like GJ 436 b that orbit close to their star. In Planetica, they appear as giant planets in calm teal and blue.

Toxic world

A toxic world is wrapped in a thick carbon dioxide atmosphere and noxious clouds, with a scorching-hot surface. If a runaway greenhouse effect kicks in, where the greenhouse effect spirals out of control, the oceans boil away and a planet can turn into one of these.

The prime example is Venus. Its surface pressure is about 90 times Earth's and its temperature soars well above 400°C, making it hotter than Mercury even though Mercury is closer to the Sun. Its sky is filled with sulfuric acid clouds. In Planetica, toxic worlds appear shrouded in dense atmosphere and clouds that hide the surface.

Barren rock

A barren rock has almost no atmosphere, leaving only bare rock and craters exposed. A planet ends up like this if it's so small that its weak gravity can't hold on to air, or if its star's intense light and wind strip its atmosphere away. With no atmosphere, the temperature difference between day and night is huge.

Mercury and our own Moon are good examples in the Solar System. Observations suggest the exoplanet LHS 3844 b is most likely a bare rock without a thick atmosphere. In Planetica, you'll see gray and brown rocky surfaces with no clouds and crisp, sharp shadows.

See for yourself in Planetica

In Planetica, each planet's type is decided by its temperature, calculated from the star's brightness and the orbital distance. That's why hot planets tend to show up on inner orbits close to the star, while ice worlds and giant planets tend to appear beyond the frost line. Try changing temperature, oceans or atmosphere in the Adjust tab to see for yourself how a planet's look changes. The planets here are all imaginary, but they're designed to follow how the real universe works.

Read more

• 9 Types of Planets
• Star Types and Colors: Spectral Classes O, B, A, F, G, K, M
• What Is the Habitable Zone (Goldilocks Zone)?