40th moon of Jupiter spotted
By Richard Stenger
CNN
(CNN) -- Using an observatory on top of a Hawaiian mountain peak, an astronomer has detected a small moon orbiting Jupiter, bringing the number of known satellites around the king of planets to 40.
Scott Sheppard of the University of Hawaii found the moon, using the school's 2.2-meter telescope atop Mauna Kea. The veteran moon hunter also took part in the discovery of 22 previous Jovian satellites.
The moon has an estimated diameter of 2.2 miles (3.5 km) and a 748-day orbit around Jupiter, according to a recent announcement from the International Astronomical Union, the world authority on celestial object discoveries in the solar system.
The largest planet, Jupiter also boasts the most identified satellites. Saturn follows with 30, and Uranus comes next with 21.
Jupiter has been called "a mini solar system" because of the many small bodies it controls through its gravity, including nearby moons and comets, and a class of distant asteroids known as Trojans.
"Since Jupiter is the largest planet in our solar system it has influenced our neighborhood second only to the sun," Sheppard said in a statement.
In recent years, the official tally of moons in the solar system has more than doubled. Saturn previously held the title of moon king with 30 known satellites, a dozen of which scientists first identified in 2000.
The latest satellite, dubbed S/2002 J1, hardly resembles Jupiter's better-known Galilean moons, the planet-size worlds of Io, Europa, Ganymede and Callisto.
Besides being much smaller, it has a more distant and elliptical orbit that carries it in a retrograde path, or one opposite the direction that Jupiter rotates.
