An introduction to exoplanets
An introduction to exoplanets

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An introduction to exoplanets

5.6  The population of known transiting planets

In Week 3 you looked at the Extrasolar Planets Encyclopaedia on the Exoplanet.eu website. At that time you just investigated radial velocity planets. This time, you’ll look at the planets detected by the transit method. 

Activity 5  Exploring Exoplanet.eu – this time it’s transits

Timing: Allow about 10 minutes

Go to the Exoplanet.eu website [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)] and click on the link labelled ‘All Catalogs’. This will take you to the Catalog screen. Below the word ‘Catalog’ you will see a drop-down menu labelled ‘Detection’. Click on this and select ‘Primary Transit’ to see all the transiting planets in the catalogue.

A little lower down, on the left-hand side of the screen, there is another drop-down menu that says ‘Show 100 entries’. Change this to ‘Show All entries’. If you scroll down the list you’ll notice that many of the transiting planets were discovered by the Kepler spacecraft, and so are named ‘Kepler’ with a numerical identifier afterwards.

As you saw in Section 3, other groups of transiting planets are also named after the project that discovered them.

From the list of transiting planets given at Exoplanet.eu, identify some of the other transit search projects. Note their names in the box below before looking at the answer.

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Answer

Transit search projects generally name their planets with a name or an acronym, followed by a hyphen that connects it to a number, which in turn is followed by a space and a lower-case letter; e.g. WASP-1 b. Projects using this naming convention include EPIC, K2, HATS, HAT-P, KELT, WASP, XO, CoRoT and Qatar.

Make a note of the number of planets discovered by:

  • i.their transits
  • ii.the radial velocity method.

Hint: use the ‘Detection’ drop-down menu to filter the results.

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Why do you think so many more planets have been discovered using the transit method than any other? Why is the radial velocity technique more difficult?

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Answer

Radial velocity measurements can only be made for bright stars by spreading the light. This requires large telescopes and specialised equipment that look at only one star at a time.

Transit searches observe many thousands of stars simultaneously, and are looking for a drop in the total amount of light from a star. This is an easier thing to measure than a small wavelength shift.

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