Jovian Planet
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Basic Information

Jupiter and Saturn represent a class of Gas Giant sometimes called a "traditional Gas Giant" or a "Jovian Planet". Such a planet is composed mostly of Hydrogen and Helium. At the very center it may have a rocky core - such a core is probably required in order for a planet to form in the first place. However, the core (and all other elements heavier than hydrogen and helium) is probably about 3% to 13% of the mass of the planet. The rest is gas. The core of such a planet may exceed 20,000oC. The atmospheric pressure near the core of a gas giant gets so intense, it turns normal hydrogen into Metallic Hydrogen - that is hydrogen that conducts electricity like a metal.

Note that the term Jovian Planet is also sometimes used more casually to mean Gas Giant in general, which includes not just these traditional gas giants, but also Ice Giants and Hot Jupiters.

In 2023, the James Webb Space Telescope detected an astonishing 80 Jovian Rogue Planets orbiting in clusters of 2. These are now known as JuMBOs.



Game and Story Use

  • You cannot "land" on a gas giant. If you go far enough down to hit something solid, you'll be destroyed by the gravity and atmospheric pressure. However, there's always the Cloud Planet option, and some aerospace vehicles may be able to fly through the hydrogen and helium clouds without too much trouble.
  • Jovian planets are usually depicted in Sci-fi as being subject to extensive atmosphere mining for spaceship fuel - presumably those isotopes of hydrogen and helium likely to be useful in a fusion reactor. Depending on the setting, this may be done from cloud cities, or by ships equipped with fuel scoops.
    • Indeed, the presence of Jovian planets capable of being "scooped" may be a key requirement for space travel - especially in an exploration phase where long range survey ships may need to self-supply without any infrastructure in place.
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