A B C D E F G H I J K L M N O P Q R S T U V W X Y Z # Select the first letter of the word from the list above to jump to appropriate section of the glossary. If the term you are looking for starts with a digit or symbol, choose the '#' link. - J - Jovian planet Massively-sized planets with low densities, that have extensive atmospheres. Jupiter Fifth planet from the Sun, and first of the Jovian planets. It is the largest planet in our solar system, and has at least twelve moons. It is visible to the naked eye, and orbits the Sun in 11.9 years. Back to Top