This is not exactly an aviation story but I apologise for the diversion. The significance of the event that I am about to describe is as great as man's first flight in 1903. The Apollo manned landings on the moon and the successful return of the space travellers to earth are by themselves some of man's greatest feats. The work now being carried out by the Mars Exploration Rover on that planet's surface is yet another major achievement.
I am however very much impressed with the journey and landing of the Cassini-Huygens (CH) spacecraft on Titan, which is Saturn's largest moon. The distance between earth and Saturn is about 1.4 billion kilometres. It took CH seven years to reach Titan. For this to happen the planets have to be ideally aligned so that CH can use the gravitational slingshot effects of earth, Venus, Jupiter and Saturn to reach Titan with the fuel that was available on board. Man would have to wait another 600 years for this alignment to occur again!
What is so interesting about Titan? It is a cloud-shrouded moon which means it is somewhat like earth but scientists want to know what its surface is like underneath the thick red clouds which are mainly composed of nitrogen and some methane Scientists believe the reddish colour of the clouds come from a substance called tholin.. There is no oxygen on Titan thus precluding man from inhabiting it. Gravity on Titan is about one-sixth that of earth but the atmospheric pressure on its surface is 1.4 times that of earth due to the thick opaque clouds that hide its surface from us.
Huygens, the lander module of CH, has succesfully sent us images and data about Titan's surface. It is almost earth-like but due to the extremely cold temperatures, all water is frozen. Rivers abound but they are not of water, rather the fluid is liquid methane since methane has a much lower freezing point. Liquid methane flows from rivers into lakes but there are only a few lakes on Titan. Past erosion by these methane rivers have created canyons and valleys not unlike what is seen in Arizona.
There are also "volcanoes" on Titan but they spew "lava" consisting of water and ammonia which flow down the slopes. Because of the cold nature of the flows these "volcanoes" are called cryovolcanoes. Other surface features of Titan include craters created by the impact of objects from space but these are few.
What about the surface material on Titan? Huygens' instruments and cameras show that the landing site is made of sand, pebbles and small rocks which are basically ice.