A closer look at Jupiter’s rotational speed

THE average distance between Jupiter and the Sun is 778 million km (about 5.2 times the average distance from the Earth to the Sun, or 5.2 AU) and it completes an orbit (one complete revolution around the sun) every 11.86 earth years. This is two-fifths the orbital period of Saturn. The elliptical orbit of Jupiter is inclined 1.31° compared to the Earth. The axial tilt (is the angle between an object’s rotational axis, and a line perpendicular to its orbital plane) of Jupiter is relatively small: only 3.13°. As a result this planet does not experience significant seasonal changes, in contrast to Earth and Mars for example. Jupiter’s rotation is the fastest of all the Solar System’s planets, completing a rotation on its axis in slightly less than ten hours; this creates an equatorial bulge easily seen through an Earth-based amateur telescope. The planet is shaped as an oblate spheroid, meaning that the diameter across its equator is longer than the diameter measured between its poles (north and south poles). On Jupiter, the equatorial diameter is 9275 km longer than the diameter measured through the poles. Because Jupiter is not a solid body, its upper atmosphere undergoes differential rotation. The rotation of Jupiter’s polar atmosphere is about 5 minutes longer than that of the equatorial atmosphere. Jupiter is usually the fourth brightest object in the sky (after the Sun, the Moon and Venus) however at times Mars appears brighter than Jupiter. Jupiter has been called the Solar System’s vacuum cleaner, because of its immense gravity well and location near the inner Solar System. It receives the most frequent comet impacts of the Solar System’s planets. It was thought that the planet served to partially shield the inner system from cometary bombardment. Jupiter’s moons Jupiter has 63 confirmed moons, giving it the largest retinue of moons with “reasonably secure” orbits of any planet in the Solar System. The most massive of them, nicknamed the four Galilean moons, were discovered in 1610 by Galileo Galilei and were the first objects found to orbit a body that was neither Earth nor the Sun. From the end of the 19th century, dozens of much smaller Jovian moons have been discovered and have received the names of lovers, conquests, or daughters of the Roman god Jupiter, or his Greek equivalent, Zeus. The Galilean moons are by far the largest objects in orbit around Jupiter, with the remaining 59 moons and the rings together comprising just 0.003 percent of the total orbiting mass. Jupiter’s Largest Moons The Galilean moons of Jupiter (Io, Europa, Ganymede and Callisto) were named by Simon Marius soon after their discovery in 1610. However, until the 20th century these fell out of favour, and instead they were referred to in the astronomical literature simply as “Jupiter I”, “Jupiter II”, etc., or as “the first satellite of Jupiter”, “Jupiter’s second satellite”, and so on. The names Io, Europa, Ganymede, and Callisto became popular in the 20th century, while the rest of the moons, usually numbered in Roman numerals V (5) through XII (12), remained unnamed. IO is the most volcanic active body in our solar system. Europa is a unique Moon of Jupiter that has fascinated scientists for hundreds of years. Its surface is among the brightest in the solar system, a consequence of sunlight reflecting off a relatively young icy crust. Its face is also among the smoothest, lacking the heavily cratered appearance characteristic of Callisto and Ganymede. Lines and cracks wrap the exterior. Europa may be internally active, and its crust may have, or had in the past, liquid water which can harbour life. The fascination with Europa began centuries ago in 1610 when Galileo Galilei discovered four Jovian satellites: Io, Callisto, Ganymede, and Europa. But only recently have people begun to learn more about the sphere. About forty years ago, modern astronomer Gerald Kuiper and others showed that Europa’s crust was composed of water and ice. In the 1970s, space exploration of Jupiter’s satellite system began with the spacecraft Pioneer and Voyager fly-by missions which verified Kuiper’s analysis of Europa and discovered other characteristics. In 1995, the Galileo spacecraft began gathering more detailed images and measurements within the system, providing the information needed to piece together Europa’s past, present, and future. calebnda1@yahoo.com