adaptive-optics

Directly imaging an exoplanet — seeing the planet itself rather than inferring it from its effect on the star — is the hardest challenge in observational astronomy. A planet is 10⁹ times fainter than its star at visible wavelengths, squeezed within 1 arcsecond of it. Yet direct imaging has been achieved for dozens of young gas giants. The HR 8799 system, with four imaged planets, was the first multi-planet system directly resolved. The ELT's next-generation coronagraphs aim to directly image Earth-like planets.

A telescope gathers more light than the eye and resolves finer detail. Galileo's 1609 refractor showed him moons around Jupiter. ESO's 39.3-meter Extremely Large Telescope collects nearly a million times more light than Galileo's lens, once adaptive optics cancels the blur of Earth's atmosphere.