Week 2: Planets, large and small

Introduction

Last week you learned about the Solar System and the planets within it. Those planets come in a range of sizes and they have very different conditions. Now that astronomers are discovering planets around other stars too, they are finding that planets are even more varied than the examples in our Solar System led us to believe. In Week 2, you’ll learn about the different classes of planet and their basic characteristics.

Watch the following video in which Carole Haswell talks about what you’ll be doing in the course this week.

Download this video clip.Video player: boc_exo_1_video_week2_carole_upload.mp4

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Transcript

Carole Haswell:

This week, you’ll be looking in more detail at the planets in our own Solar System. They’re the only planets in the Universe we can get such detailed information on, so it’s important to know a bit about them before you move on to planets orbiting other stars.

We can’t see exoplanets directly, except possibly in a few very special cases. And we have to be quite clever to work out their properties. Until we started to discover exoplanets, I was much more interested in other parts of astronomy. But exoplanets offer so much scope for the imagination.

I love the cleverness of the techniques that we’ve developed to learn about exoplanets. There’s something almost like fate in the fact that modes of thought, which humans have evolved to survive on Earth, allow us to work out so much about remote objects we can’t see.

It’s almost as though the Universe is there specifically for us to exercise our ingenuity and to see how far it takes us. Now, to get very far in astronomy, or any other science, you need to know some maths. And this week is probably the most maths intensive.

But by the end of it, you should be able to deal with literally astronomical sized numbers. You can still pass the course without mastering the maths, but your appreciation of astronomy will be much deeper if you can become fluent in the maths we use. You might even get to enjoy it. I do. Right then. Let’s get on with it.

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By the end of this week, you will be able to:

• describe what is meant by a terrestrial planet and a giant planet, and the differences between these two planet types
• understand the scale of the Solar System and use the astronomical unit to measure it
• classify the planets Jupiter, Saturn, Uranus and Neptune as gas giants or ice giants
• describe what is meant by mass, radius, volume and density, and how these terms are used within astronomy
• understand the meaning of the symbols AU, M_J, R_J, M_E, R_E, M_⊕, R_⊕, M_Sun, R_Sun, M_⊙ and R_⊙.