Giant planet landing on a giant planet may or may not be possible, depending on the size and composition of its core. Gas giants consist mostly of hydrogen and helium. The Solar System's gas giants, Jupiter and Saturn, have heavier elements making up between 3 and 13 percent of their mass. Gas giants are thought to consist of an outer layer of molecular hydrogen, surrounding a layer of liquid metallic hydrogen, with a probable molten core with a rocky composition. Jupiter and Saturn's outermost portion of the hydrogen atmosphere has many layers of visible clouds that are mostly composed of water and
Red giant system, if present, uninhabitable, some research suggests that, during the evolution of a star along the red-giant branch, it could harbor a habitable zone for several times 10 years at 2 AU out to around 10 years at 9 AU out, giving perhaps enough time for life to develop on a suitable world. After the red-giant stage, there would for such a star be a habitable zone between 7 and 22 AU for an additional 10 years. Later studies have refined this scenario, showing how for a star the habitable zone lasts from 10 years for a planet with an