Roman Space Telescope's New Coronagraph Will Directly Image Distant Planets

NASA's Nancy Grace Roman Space Telescope, which launched August 30, is carrying the most advanced coronagraph ever flown in space — an instrument that can block out a star's light so planets orbiting it become directly visible, according to Dominic Benford, the telescope's program scientist.

A coronagraph works like an artificial eclipse: it blocks a star's overpowering light so that fainter objects nearby, such as orbiting planets, can be seen. Astronomers have used coronagraphs to study the sun's own corona for more than a century, including on NASA's PUNCH (Polarimeter to Unify the Corona and Heliosphere) mission, which launched in 2025, and its SOHO (Solar and Heliospheric Observatory). The James Webb Space Telescope and Hubble Space Telescope also carry coronagraphs for observing planets beyond the solar system, though Roman's is considerably more advanced.

Instead of a simple physical mask, Roman's coronagraph uses patterned disks and special filters to create destructive interference, in which competing light waves cancel each other out. Benford said the instrument can block starlight down to just a few parts per billion, letting through only light reflecting off a planet — "something like a Jupiter around another star, which we've never been able to do before."

Roman's coronagraph is also the first "active" one flown in space: hundreds of tiny pistons built into its mirrors let it adjust their shape in real time to correct distortions, commanded with precision approaching the size of an atom, according to Vanessa Bailey, the coronagraph's instrument scientist. If it works as designed, the coronagraph should be capable of detecting exoplanets about 100 million times fainter than their host stars.

Bailey said the team is especially interested in a handful of nearby star systems where hints of unseen Jupiter-like planets have already been found, as well as dust and debris left over from planet formation.