Planets around other stars — Astronomy, 7–10 years
An exoplanet is a planet orbiting a star beyond our Solar System. Most are too far away and too faint to photograph directly, so astronomers find them by noticing how they affect their star.
Other stars can have planets
Our Sun is not the only star with worlds going around it. A planet orbiting another star is called an exoplanet. Some are giant balls of hot gas, while others may be rocky, but they are all so distant that their star usually outshines them.
Why look for exoplanets?
For a long time, we could see planets only in our own Solar System, so we did not know whether planetary systems were common. Finding other worlds helps scientists compare different systems and ask how planets form. Studying their atmospheres may also show which conditions exist there.
Finding 51 Pegasi b
1. Astronomers watched the star 51 Pegasi and measured tiny changes in its motion. 2. A planet’s gravity made the star wobble slightly as the planet orbited. 3. The wobble repeated about every four days. 4. In 1995, this pattern revealed 51 Pegasi b, the first planet found around a Sun-like star.
A wobbling star is not a broken star
It is reasonable to think a star’s small movement is a mistake in the telescope or a change inside the star. Astronomers therefore check that the signal repeats and matches an orbit. A planet and its star both pull on each other; the star’s tiny wobble is the clue.
Searching for places beyond Earth
Exoplanet research helps scientists identify worlds with different sizes, temperatures and atmospheres. A planet in a star’s habitable zone may have temperatures that allow liquid water, but that does not prove it has life. New telescopes can study some of these atmospheres for useful clues.
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