Credit: NASA/JPL/Space Science Institute

NASA recently published a beautiful image of two Saturnian moons, acquired by the Saturn-orbiting Cassini spacecraft. The image shows Titan, Saturn’s largest moon, beyond its smaller companion Tethys.

Titan (5,150 km across), the second largest moon in the Solar System, after Ganymede (5,250 km across), Jupiter’s largest satellite, is a unique moon. While several planetary moons have very tenuous atmospheres, Titan has a dense atmosphere, whose surface pressure is 1.5 times that of Earth. Thick smog, in Titan’s atmosphere, almost totally obscures the surface of the moon. However, radar and infrared imaging devices, onboard Cassini, which are capable of penetrating Titan’s atmospheric haze, have revealed Titan’s surface, and showed it is dominated by broad dark and bright terrains. Intriguingly, Cassini has also detected lakes of liquid hydrocarbons, in the polar regions of cold Titan. This discovery makes Titan the only celestial object to have bodies of liquids on its surface.

Since Titan’s atmosphere is composed mostly of nitrogen, scientists believe that the current conditions on Titan resemble those that prevailed in early stages of Earth’s evolution, billions of years ago. Remarkable geological features can be seen on icy Tethys (1,062 km across), including a long valley, technically known as Ithaca Chasma, running for 2,000 km. This valley is believed to have been formed due to a massive impact with a large meteorite.   

The image was taken with Cassini’s narrow-angle camera, on 18 October 2010. The spacecraft was approximately 2.5 million km from Titan, and 1.5 million km from Tethys.

Tethys orbits Saturn every 1.9 days, at a distance of approximately 295,000 km. Titan orbits Saturn every 16 days, at an average distance of about 1,220,000 km. Most of the satellites of the Solar System have been named after mythological characters. The names Titan and Tethys come from Greek mythology. 

References

NASA’s Photojournal

Wikipedia

Further Reading

The Cassini Mission Homepage

http://saturn.jpl.nasa.gov/

Aymen Mohamed Ibrahem

Senior Astronomy Specialist