Moons
Moons

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Moons

1.1.1 Getting started with moons

Figure 1

In the previous video, Keri Bean mentioned that the two moons of Mars are small and that these are probably captured asteroids, whose orbits are still changing significantly. Others then spoke about the moons that show the most obvious signs of present-day activity:

  • Io, a moon of Jupiter, which is a rocky body with active volcanoes that colour its surface with sulfur
  • Europa, another moon of Jupiter, with a rocky interior but an outer layer of ice and probably a global ocean sandwiched between the two
  • Enceladus, a small icy moon of Saturn with a young, fractured surface and jets of ice crystals vented into space
  • Titan, Saturn’s largest satellite, which has a dense atmosphere shrouding an icy surface that has rivers and lakes of liquid methane.

One important point that is not clearly mentioned is the low temperatures prevailing in the outer part of the Solar System. Out at Jupiter, whose distance from the Sun is five times the Earth’s, the average surface temperature on a moon is minus 170 degrees centigrade. The further from the Sun, the colder it gets: minus 200 degrees centigrade for Saturn’s moons, minus 210 degrees at Uranus, and minus 235 degrees at Neptune. This means that except where there is an internal heat source, the ice that forms the outer layers of all large moons (except the Moon and Io) is so cold, strong and rigid that it behaves exactly like rock does on the Earth or on the Moon.

Attention was also drawn to the Pluto–Charon system (which had not yet been visited when the video was made). Pluto is a dwarf planet made of ice. It is no longer counted as a true planet, but as one of the largest and nearest Kuiper Belt objects. Its major moon, Charon, has a diameter that is slightly more than half that of Pluto. Pluto and Charon are so close to each other that tidal forces have locked their rotations so that each keeps the same face permanently towards its partner. If you like, you can think of Pluto–Charon as a double object, rather than a main body plus a moon.

The video then turned to the Moon, meaning the moon that orbits the Earth. You will learn much more about the Moon later on, but the scientists gave you some hints about why this is an important body.

The video concluded by speculating about moons that could host life and about how resources from the Moon could open up the way for future exploration of the Solar System.

MOONS_1

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 over 40 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, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 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 prospectus