Dione and Tethys have little companion moons that orbit along with them. Tethys itself features a canyon called Ithaca Chasma that goes three quarters of the way around the moon. In the four years it will explore the Saturnian system, Cassini will visit Titan almost every time it circles the planet. On one pass, Cassini will drop a probe built by the European Space Agency and named Huygens. As it uses its two parachutes to descend 90 miles to the surface of Titan, it will analyze the chemistry of Titan s atmosphere.
Scientists know Titan has a thick atmosphere, which is unusual for a moon.
They also think the atmosphere is full of nitrogen and may be similar to early earth. Scientists theorize the surface is an ocean of liquid methane or ethane. There s a microphone on the probe, to send back the sound of touchdown. Thomas O Toole is a freelance writer and former editor of Aerospace America magazine who covered space during much of his 21 years at the Washington Post. Huygens probe descends to Titan.