Moons of our Solar System
Moons of our Solar System

Start this free course now. Just create an account and sign in. Enrol and complete the course for a free statement of participation or digital badge if available.

Free course

Moons of our Solar System

1.2 Distance from the Sun is important too

The further out from the Sun a moon has formed, the more exotic the materials it is made of. Salts and volatiles all have the effect of lowering the melting temperature of the ice, making it easier for the moons to show signs of geological activity even if there is little internal heat. The richest-known cocktail of ices occurs on Neptune’s large moon Triton, whose surface appears to be mostly water-ice and frozen carbon dioxide, with traces of methane, carbon monoxide and probably ammonia. In addition, it has seasonal polar caps of nitrogen-ice.

Described image
Figure 7 The surface of Titan as seen from ground-level by the Huygens lander. The largest pebble in the foreground is about 15 cm across.

Titan, the largest moon of Saturn, has a dense atmosphere composed mainly of nitrogen but with methane and other hydrocarbons forming clouds and haze. It sometimes rains methane and there are vast lakes of methane at the surface. The ground surface (which is made of water-ice that behaves as rock behaves on Earth) is eroded by rivers of methane creating visible channels and river beds. We know this because of the Cassini–Huygens mission. This mission was a joint venture of ESA and NASA and was a massive success. It reached Saturn in July 2004, with the Huygens lander touching down on Titan in January 2005. This gave us the most distant ground-level view yet achieved. Figure 7 is the surface of Titan taken by the Huygens lander. The thick orange haze is high in the nitrogen- and methane-based atmosphere. The pebbles are not in fact rock, but are water-ice.

See an artist’s impression of a methane rainstorm on Titan in this Astronomy Picture of the Day [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to University-level study, we offer two introductory routes to our qualifications. You could either choose to start with an Access module, or a module which allows you to count your previous learning towards an Open University qualification. Read our guide on Where to take your learning next for more information.

Not ready for formal University study? Then browse over 1000 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus371