tech

Transmission spectroscopy

A technique for reading a distant planet's atmospheric composition by light. As the planet crosses the face of its star, a thin sliver of starlight strains through its atmosphere on the way to us; each gas absorbs light at characteristic wavelengths, leaving a "fingerprint" in the spectrum. Split that light and you read the air recipe of a world you can never visit. The James Webb Space Telescope uses this method to detect CO₂, water vapour, and methane on exoplanets.