17 September 2010
Credit: NASA/JPL/Space Science Institute
NASA recently published a wonderful image of Janus, a small, irregularly-shaped moon of Saturn, the ringed giant planet. The image was acquired by the Saturn-orbiting Cassini spacecraft. It shows that Janus (179 km across) features light and dark impact craters.
Cassini was looking toward the Saturn-facing side of rugged Janus. The image was taken in visual light, with the Cassini spacecraft narrow-angle camera, on 7 April 2010. Cassini was approximately 75,000 km from Janus.
Intriguingly, Janus has unique dynamical properties. The orbit of Janus is extremely close to that of another small Saturnian moon, known as Epimetheus (113 km across). These two orbits are separated just by about 50 km! Due to the mutual gravitational influence between Janus and Epimetheus, the two moons exchange orbits, once every four years, approximately.
Janus orbits Saturn every 16.6 hours, at an average distance of approximately 150,000 km. For comparison, our Moon (3,476 km across) orbits Earth every 27.3 days, at an average distance of approximately 384,000 km. The majority of moons have been named after mythological characters. In Roman mythology, Janus was the god of gates, doors, beginnings and endings.
References
NASA’s Photojournal
Wikipedia
Further Reading
The Cassini Mission Homepage
http://saturn.jpl.nasa.gov/index.cfm
Aymen Mohamed Ibrahem
Senior Astronomy Specialist