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An introduction to exoplanets
An introduction to exoplanets

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1  Exoplanet names

All planets outside our own Solar System are given a name that tells you which star they belong to. The planet’s name is the star’s name with a lower-case letter added, so for instance 51 Pegasi b is the first planet found orbiting the star 51 Pegasi. If a second planet is found orbiting this star, it will be called 51 Pegasi c.

In some systems several planets are known; for example, Kepler-444 b, Kepler-444 c, Kepler-444 d, Kepler-444 e, and Kepler-444 f are the five planets orbiting the star Kepler-444. Astronomers use only lower-case letters to designate planets.

Activity 1  What’s in a name?

Timing: Allow about 5 minutes

What can you say immediately about these planets?

  1. Aldebaran b


Aldebaran b is the first planet discovered orbiting the star called Aldebaran.

  1. HD 96700 c


HD 96700 c is the second planet discovered orbiting the star called HD 96700. This name is just a catalogue number.

  1. K2-19 d


K2-19 d is the third planet discovered orbiting the star called K2-19.