The Gas Giant Planets

There are four planets in our solar system that qualify as Gas Giants but two of them are sub classified as “ice giants” and while all are thought to have a rocky core, it isn’t in reference to a solid ball of rock. These discrepancies are just the tip of the ice berg that is unknown about the gas giant planets, but is guessed at by science.

A Look at the Gas Giant Planets

Also known as “Jovian Planets” after the biggest of the lot, Jupiter, the four gas giants in our solar system are Jupiter, Saturn, Uranus and Neptune. All four are called gas giants for two very simple reasons; they are gigantic in proportion to Earth, and they are comprised primarily of gas. It is there the simple ends and the difficult begins as astronomers struggle to classify and quantify these near- neighbours.

These planets are believed to have a core of rock, but it is believed that the core is not exactly what you might image a “rocky core” to be. The internal temperatures of these gas giants is intense, ranging from 7,000 Kelvin to 20,000, so any core is likely to be liquid. The rocky core is actually referring to a liquid core of heavier elements such as iron and nickel. The fact that the concentration of these heavier elements is higher at the core than elsewhere led to calling it a “rocky core.”

The Gas of the Giant

All four giant planets are mostly comprised of hydrogen and helium and other like elements in various concentrations. When it comes to Uranus and Neptune, however, the greater amounts belong to ammonia, methane and water, leading to the sub classification of “ice giants.” Like the labelling of the rocky cores, however, don’t be fooled into thinking these planets are solid balls of ice. In fact Uranus is believed to be covered in a liquid ocean of water and ammonia. For the most part there is no clear separation of a “surface” and an “atmosphere” on these planets beyond possibly arbitrary designations.

Nomenclature

In fact the term “gas giant” was a bit of an arbitrary distinction, coined in 1952 by James Blish, a science fiction writer. While there is almost no distinction between gas and liquid on these planets, terrestrial scientists have stuck to a naming process that links elements to “gas”, “rock” and “ice” irrespective of their actual state. Silicates are termed rock, ice refers to water and ammonia, and helium and hydrogen are gas. Even the term “Jovian” is misleading from its original intent- to classify planets that are like Jupiter. It applies well to Saturn, but Uranus and Neptune, the ice giants, are sufficiently different to be excused from the nomenclature; but it remains a popular term.

Final Thoughts

The inefficiency and arbitrary nature of assumptions and terminology teaches us a lot about the process of astronomical exploration. As we push out beyond the boundaries of the solar system and encounter extrasolar gas giants, we may find we have to start from scratch in our understanding of the planets.