Gas Giant
A gas giant is what? A massive planet primarily made of helium and/or hydrogen is referred to as a gas giant. These planets feature swirling gases atop a solid core rather than hard surfaces, similar to Jupiter and Saturn in our solar system. Exoplanets that are gas giants can be far bigger than Jupiter and orbit their stars much more closely than any planets in our solar system. Our knowledge of the formation and evolution of planets for the most of human history was based on the eight (or nine) planets in our solar system. But during the past 25 years, more than 4,000 exoplanets, or planets outside our solar system, have been found, and this has completely transformed everything. Helium and/or hydrogen make up the majority of gas giants in our solar system, such as Jupiter and Saturn. "Hot Jupiters" are gas giants that are located closer to their stars. Within these broad groups is much diversity. For example, hot Jupiters, which are gas giants like Jupiter but orbi...