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


1.1 Fascinating bodies

To make this video, we gathered comments about moons from scientists attending the 2013 Lunar and Planetary Science Conference in Houston, Texas. Christine Shupla, who will appear again in later videos, spoke about different kinds of moons. The single thing that they all have in common is that each of them orbits a larger body. This larger body is usually a planet, but there are many bodies too small to be classified as planets that also have their own moons.

The giant planets Jupiter, Saturn, Uranus and Neptune each have some large moons, comparable in size to our own Moon. Most of these moons probably formed around their planet. But each giant planet also has numerous smaller moons, which are irregular in shape because the moon’s own gravity is too weak to pull it into a sphere. Some of these irregular moons are in orbits very close to their planets and are probably debris from bigger moons destroyed by collisions or ripped apart by tides. These are sometimes called ‘inner moonlets’. Other irregular moons orbit much further from their planet and are probably wanderers such as comets (mostly ice) or asteroids (mostly rocky) that became captured after straying too close by chance.

Download this video clip.
Skip transcript


When we think of interesting bodies in our Solar System, the first that may come to mind are our planet Earth, or Mars, or the large gas planets. But perhaps even more intriguing, attracting scientists and curious minds from far and wide, are the bodies that orbit around planets: MOONS.
If I were to think of the most interesting thing about moons I would say just how different they are from each other.
It's important to study moons because they can give us information about how their planetary bodies are perhaps formed, like in the case of Earth
Our fascination with the Earth's Moon dates back to the beginning of human existence. But in 1610, Italian astronomer Galileo made a key discovery. He observed through his telescope what we now know are the four largest moons of Jupiter. This was important proof that everything in the Solar System does not revolve around the Earth. It was also the first of many moon discoveries to come.
Our Solar System's number of moons has been steadily increasing over time. They find new ones every year. Earth has one Moon, Mars has two.
Phobos and Deimos are the two moons of Mars, we believe that they are captured asteroids. Deimos is really tiny and it's actually being flung away from Mars. Phobos is kind of a bigger moon, and it's actually going to eventually crash into the surface of Mars.
When you get to the gas giants, they have immense amounts of gravity, and their wide orbits have 1enabled them to pick up many moons, some of them probably formed in orbit around the planets, others are captured asteroids and comets.
Io is a, is the best moon of Jupiter. The surface of Io is covered in sulfur, and that's because there are hundreds of active volcanoes erupting on Io's surface.
Europa's surface is very young, only about 60 million years old. Europa is intriguing because we think it has an ocean below its surface.
Nobody expected Enceladus to be an exciting place. You can see crystallised water ice with ammonia and various organic compounds being jetted into space.
Titan is, I would say, quite unique. Titan does have lakes and even seas of liquid methane.
Pluto and Charon, its moon, are locked in rotation. As one rotates and the other orbits they keep the same face facing towards each other. It's the nearest thing we have to a double planet.
My favourite moon does have to be our Moon, the Earth's Moon. That's the only place in our Solar System that we are likely to be able to go and find a piece of early Earth.
The first man-made object to reach our Moon was the Soviet Luna 2, that crash landed in September 1959. We got our first blurry view of the Moon's far side from Luna 3. Later, the Apollo manned landings gathered an incredible wealth of first - hand information about the lunar surface, some of which we are still trying to understand today.
We can get some very, very interesting chemical data out of the Moon not available to us by looking at rocks from the Earth.
It became evident that the Moon was something else than just this odd object floating around the Earth. It's a critical part of the Earth - Moon system. It is really a part of us.
The Moon may also tell us the story of how the Solar System came to be.
When you think about our Moon, it probably has the most complete and clear history available of the last four and a half billion years of Solar System evolution. There's really no other world like it.
Moons may hold the answer to our eternal question, are we alone?
Are there places in the Solar System, where life could exist today? Does Europa have what we call chemical energy that could power life?
In our quest for the answers to the secrets of the universe, each moon can shed light on a different corner of the puzzle and bring us closer to new discoveries we could never have thought possible.
It's literally unlimited the amount of potential resources that we may find and use on the Moon. It's really, the only limitation is our own imaginations. There's no place we can't go, there's no place we can't live.
End transcript
Copy this transcript to the clipboard
Print this transcript
Interactive feature not available in single page view (see it in standard view).

At the next (2014) Lunar and Planetary Science Conference, Professor David Rothery managed to grab this bonus video message for learners on this course from an Apollo astronaut.

Interactive feature not available in single page view (see it in standard view).

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