NASA's Roman telescope to use active coronagraph for exoplanet imaging

NASA’s upcoming Nancy Grace Roman Space Telescope, slated for launch as early as the end of next month, will carry the first active coronagraph ever deployed in space. This instrument is designed to block out most of a star’s light, enabling astronomers to directly image planets orbiting other stars—particularly ones similar to those in our own solar system. The mission could eventually pave the way for a future telescope to capture the first pictures of Earth-like worlds.

The telescope will affect the field of exoplanet science by allowing researchers to see smaller, dimmer, and more close-in planets than ever before. Unlike previous coronagraphs on Hubble and the James Webb Space Telescope, which use static blockers, Roman’s system employs active wavefront control. It measures leftover starlight and suppresses it using two deformable mirrors, each with a 48-by-48 grid of tiny actuators that can adjust the mirror surface by as little as 10 picometers—about a tenth the diameter of a hydrogen atom. This technique is expected to improve sensitivity to exoplanets by a factor of up to 1,000 compared to current space-based coronagraphs.

This matters because nearly all exoplanets photographed so far are massive, young, and far from their stars—nothing like the planets in our solar system. Roman could directly image a true Jupiter analogue: a mature gas giant orbiting a sunlike star at a distance a few times Earth’s orbital radius. Such a planet would be primarily reflecting its star’s light, not glowing from internal heat. The telescope’s wide-field camera, with roughly 300 megapixels, will also capture images about 100 times larger than Hubble’s widest exposures at similar resolution, helping astronomers study dark matter, dark energy, and detect around 100,000 new exoplanets.

Background: The Roman Space Telescope is named after Nancy Grace Roman, NASA’s first chief of astronomy. It will carry both a wide-field camera and the coronagraph instrument. The coronagraph uses masks, including “silicon grass”—microscopic spikes that trap photons to prevent stray light from reaching detectors. Javier Viaña, a Harvard research scientist with projects selected for Roman’s first year of observing, compared the leap to moving from “interviewing a handful of people” to “conducting a global census.”

Next steps: The telescope is expected to launch by the end of next month. Once operational, it will begin observing stellar systems one at a time with the coronagraph, aiming to directly image exoplanets that have been too faint to see. Success could demonstrate the technology needed for a future mission to photograph Earth-like planets, fulfilling what lead mechanical engineer Brandon Creager calls a “critical stepping stone for … finding Earth 2.0.”