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

1.3.13 Moons data

This downloadable PDF [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]   takes you to a table of data for the moons of all the planets plus Pluto. You may find this a useful source of reference as you progress through the course. However we would like you to consult it now to look a little further into orbital resonances. The only column of data that you need to look at for this purpose is the one listing orbital periods.

Activity 3

The table lists the orbital periods of Io, Europa and Ganymede as 1.769, 3.551 and 7.155 days. To verify that these are resonant orbits, you need to divide one period by another. For example the ratio between Europa’s and Io’s period is 3.551/1.769. If you use a calculator this works out at 2.00734878. The final digits are meaningless, and this number rounds down to 2.0. Similarly dividing Ganymede’s period by Io’s period 7.155/1.769 works out at 4.0.

But what about Callisto? Its orbital period is 16.689 days. Does this share an orbital resonance with the others?

Try dividing its orbital period by Ganymede’s, and see what you get.

Answer

Dividing Callisto’s 16.689 day orbital period by Ganymede’s 7.155 day orbital period works out at 2.33249, or 2.3. This shows that Callisto’s orbit is not resonant with Ganymede’s.

To finish off, go back to the table and take a quick look at Saturn’s satellites. Can you find any orbital resonances there? (Hint: you may have to look beyond a moon’s immediate neighbour.)

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