A very little extraterrestrial world has recently been discovered Orbited the Solar System’s nearest star neighbour. Proxima d is an exoplanet candidate that circles Proxima Centauri, a small, faint red dwarf star just 4.2 light-years from the Sun. Surprisingly, the exoplanet is only a fourth of Earth’s mass. It’s one of the tiniest exoplanets ever discovered, and the tiniest ever discovered through observing the exoplanet’s gravitational effect on its star.
It’s also the third exoplanet discovered around Proxima Centauri, and while the newly discovered world isn’t livable, its identification shows that there’s a whole world of exoplanets out there just beyond our current capabilities. Nearly 5,000 exoplanets (planets outside our Solar System) have been identified and confirmed to date, while thousands more candidate exoplanets have been detected.
When two bodies are gravitationally bound, such as a star and a planet, one does not Orbited the other. Instead, they revolve around their common mass centre; the Solar System’s barycenter, for example, sits just beyond the Sun’s surface. The star ‘wobbles’ slightly on the spot as a result of this, generating a Doppler shift in the light that reaches us. The wavelengths of the star’s light stretch out slightly as it moves away from us; as it moves closer, they compress. Astronomers can deduce the presence of an exoplanet by looking for those frequent Doppler changes.