The awards for 2019 were announced today and half went to P. J. E. (James) Peebles for his theoretical work in physical cosmology and the other half jointly to Michel Mayor and Didier Queloz for the first discovery in 1995 of an exoplanet orbiting a solar-type star. By now more than 4,000 exoplanets have been found.
Directly observing a planet orbiting a star other than the Sun is not easy since stars are distant and planets are ‘dark’ (i.e., not primary sources of light). We directly see stars but not planets. Mayor and Queloz tried to see if they could detect the existence of a planet by the fact that due to gravity, the star and the planet orbit around their common center-of-mass. As the star moves towards us during its orbit, the light is blue-shifted and when it is moving away it is red-shifted and it is this ‘wobble’ that they were looking for. But since stars are so much more massive than planets, this wobble is usually tiny. For it to be significant, the planet’s mass should be large but usually large mass planets have large orbital periods, making the detection of variations in light frequency hard. For example, the largest planet in our Solar System is Jupiter that has an orbital period of almost 12 years.
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