Kepler to Exoplanets

Kepler derived his three laws from Tycho Brahe's naked-eye data in the 1600s. Newton later showed they all follow from one principle: gravity pulls with a force proportional to 1/r². This inverse-square law turned Kepler's observations into a single unified theory that governs planets, comets, and satellites alike.

The same math finds exoplanets. In 1995, the first planet around a Sun-like star was caught by the wobble it tugs into its star — the radial-velocity method, where the period and size of the wobble reveal the planet's mass and distance. But most of the 5,000+ exoplanets confirmed since have been found a second way: the transit method, watching for tiny dips in starlight as a planet crosses its star, the technique behind NASA's Kepler and TESS surveys.