<P> A giant planet is a massive planet and has a thick atmosphere of hydrogen and helium . They may have a dense molten core of rocky elements, or the core may have completely dissolved and dispersed throughout the planet if the planet is hot enough . In "traditional" giant planets such as Jupiter and Saturn (the gas giants) hydrogen and helium constitute most of the mass of the planet, whereas they only make up an outer envelope on Uranus and Neptune, which are instead mostly composed of water, ammonia, and methane and therefore increasingly referred to as "ice giants". </P> <P> Extrasolar giant planets that orbit very close to their stars are the exoplanets that are easiest to detect . These are called hot Jupiters and hot Neptunes because they have very high surface temperatures . Hot Jupiters were, until the advent of space - borne telescopes, the most common form of exoplanet known, due to the relative ease of detecting them with ground - based instruments . </P> <P> Giant planets are commonly said to lack solid surfaces, but it is more accurate to say that they lack surfaces altogether since the gases that constitute them simply become thinner and thinner with increasing distance from the planets' centers, eventually becoming indistinguishable from the interplanetary medium . Therefore, landing on a giant planet may or may not be possible, depending on the size and composition of its core . </P> <P> 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 . </P>

Which of these is not true about the jovian planets