Gas giant (noun, “GASS GYE-ent”)
This word describes a large planet made up of mostly light elements such as hydrogen and helium. This kind of planet lacks a solid surface like Earth’s. Instead, below the atmosphere, high pressures squeeze hydrogen gas into a liquid. A gas giant may contain a rocky core buried deep within, but scientists are still learning what such a core would look like.
In our solar system, Jupiter and Saturn are gas giants. These planets make Earth look tiny. The diameter of Jupiter is 11 times bigger than that of Earth, and Saturn’s is nine times bigger. Some people also include Uranus and Neptune in the gas giant category. They have a lot of hydrogen and helium in their atmospheres. But these planets also have water, methane and ammonia, and so NASA places them in their own group.
Astronomers have spotted gas giants outside our solar system. Like Jupiter and Saturn, they aren’t very dense. But they can be even bigger or hotter than our solar system’s gas giants.
In a sentence
Astronomers have observed a sizzling-hot gas giant some 650 light-years away from earth.