Skip to content
Skip to main content

About this free course


Download this course

Share this free course

An introduction to exoplanets
An introduction to exoplanets

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.

10  Summary of Week 6

This week, you’ve learned about the planetary population of the Milky Way. The large sample of stars studied by the Kepler space telescope has given us a lot of information about the kinds of planets that are likely to be in the Milky Way. You’ve also learned why these numbers are important for scientists trying to predict whether there are other habitable worlds out there. You’ve even seen an introduction to the scientific assessment of whether alien life is likely.

You’ve learned that it’s more difficult to detect some types of planets than others. In particular, it is difficult to find small planets in wide orbits. It is relatively easy to find large planets in close orbits, so the numbers of each type of known planet are very heavily biased. Fortunately, we can correct this by using the probability of detection. This allows us to work out what the Galaxy’s population of planets is truly like. All else being equal, it’s also much easier to detect and find out about planets orbiting stars that are relatively near. Recently, surveys have started to look for small, potentially habitable planets around nearby cool stars. These surveys have met with some success.

You should now be able to:

  • know that there are more planets than stars in the Milky Way
  • explain in words how we know this
  • describe the relative abundance of terrestrial and giant exoplanets
  • know why some exoplanets are much easier to detect than others, using the radial velocity (RV) and transit methods for planet discovery
  • understand the use of light years for measuring distance
  • understand and explain in words the concept of a habitable zone
  • explain why, despite their abundance, we know of relatively few terrestrial exoplanets.

Next week, you’ll be studying some of these small planets, as well as the most interesting of other larger planets.

You can now go to Week 7 [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] .