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

2.5 The habitable zone

Since liquid water is essential to life as we know it, the surface temperature of the planet or moon really matters: it should be between 0 °C (the freezing point of water) and 100 °C (the boiling point of water).

The most important factor that determines temperature on a planet’s or moon’s surface is its distance from the Sun. If the planet or moon is too close, it gets too hot; if it is too far away, it is too cold. Currently, the only bodies inside the habitable zone of the Sun are the Earth and the Moon. But the Moon has a very hostile surface, with temperatures varying between +120 °C during the lunar day and −150 °C during the lunar night. The reason for these extremes is that the Moon is too small to hold an atmosphere, and so its sunlit side heats up quickly and its night side cools quickly.

Looking at Figure 11 suggests that there is little hope, from this point of view, of finding habitable environments elsewhere. However, the Earth–Moon comparison shows that being in the habitable zone is not the only determining factor.

Described image
Figure 11 Distance from the Sun determines the zone where liquid water can occur, known as the habitable zone.

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