divine pantheon: Zeus to the Greeks and Jupiter to the Romans. The International Astronomical Union formally adopted the name Jupiter for the planet in 1976, and has since named its newly discovered satellites for the god's lovers, favourites, and descendants. The planetary symbol for Jupiter, , descends from a Greek zeta with a horizontal stroke, , as an abbreviation for Zeus. In Germanic mythology, Jupiter is equated to Thor, the namesake of Thursday. It has been theorized that this replaced the Latin name for the day, Dies Iovi ('Day of Jupiter'). The Latin name Iovis is associated with the etymology of Zeus ('sky father'). The English equivalent, Jove, is only known to have come into use as a poetic name for the planet around the 14th century. The original Greek deity Zeus supplies the root zeno-, which is used to form some Jupiter-related words, such as zenographic. Jovian is the adjectival form of Jupiter. The older adjectival form jovial, employed by astrologers in the Middle Ages, has come to mean 'happy' or 'merry', moods ascribed to Jupiter's influence in astrology. Formation and migration Jupiter is believed to be the oldest planet in the Solar System. Current models of Solar System formation suggest that Jupiter formed at or beyond the snow line: a distance from the early Sun where the temperature is sufficiently cold for volatiles such as water to condense into solids. The planet began as a solid core, which then accumulated its gaseous atmosphere. As a consequence, the planet must have formed before the solar nebula was fully dispersed. During its formation, Jupiter's mass gradually increased until it had 20 times the mass of the Earth, approximately half of which was made up of silicates, ices and other heavy-element constituents. When the proto-Jupiter grew larger than 50 Earth masses it created a gap in the solar nebula. Thereafter, the growing planet reached its final masses in 3–4 million years. According to the "grand tack hypothesis", Jupiter began to form at a distance of roughly from the Sun. As the young planet accreted mass, interaction with the gas disk orbiting the Sun and orbital resonances with Saturn caused it to migrate inward. This upset the orbits of several super-Earths orbiting closer to the Sun, causing them to collide destructively. Saturn would later have begun to migrate inwards too, much faster than Jupiter, until the two planets became captured in a