säteittäisnopeusmenetelmä

The säteittäisnopeusmenetelmä, or radial velocity method, is a technique used to detect exoplanets. It works by observing the slight wobble of a star caused by the gravitational pull of an orbiting planet. As a planet orbits a star, its gravity tugs on the star, causing the star to move back and forth. This movement, though very small, can be detected by observing the star's light.

Specifically, the method relies on the Doppler effect. When a star moves towards an observer, its light is shifted to shorter, bluer wavelengths (blueshift). When it moves away, its light is shifted to longer, redder wavelengths (redshift). By measuring these shifts in the star's spectrum over time, astronomers can determine the star's radial velocity – its speed towards or away from us.

A periodic change in the star's radial velocity indicates that it is being influenced by the gravitational pull of an unseen companion, most likely a planet. The amplitude of the radial velocity variation is related to the planet's mass and its orbital distance, while the period of the variation corresponds to the planet's orbital period. The säteittäisnopeusmenetelmä is most effective for detecting massive planets orbiting close to their stars, and it has been responsible for the discovery of thousands of exoplanets. It provides crucial information about a planet's minimum mass and orbital characteristics, making it a cornerstone of exoplanet research.