Two mirrors, each small enough to rest in a person's palm, are poised to transform how astronomers search for planets beyond our solar system. NASA's Nancy Grace Roman Space Telescope, set to launch soon, carries an experimental coronagraph equipped with adaptive optics technology that will attempt to directly capture starlight bouncing off a planet's surface for the first time. The demonstration aims to pave the way for a future space telescope capable of glimpsing an Earthlike world circling a sunlike star—a goal that remains beyond current engineering capabilities.
The coronagraph's two palm-sized mirrors represent the agency's first attempt to fly active deformable mirrors in space. Each mirror contains roughly 2,300 tiny actuators that expand when hit with a small electrical charge, infinitesimally reshaping the mirror to counteract light distortions. The system also relies on extremely sensitive detectors that amplify signals from individual photons—essential given how few photons the instrument will capture from any planet—and a set of intricately detailed masks that serve as star shades. The challenge is immense: NASA likens the coronagraph's task to photographing a firefly sitting beside a floodlight from across the country, where any stray starlight in the wrong location could ruin an entire portion of the image.
During operations, scientists will test the coronagraph by attempting to spot several known exoplanets. "If we go through the whole thing and we don't see them, then we know something is wrong with the coronagraph, because those planets are there," says Margaret Turnbull, an exoplanet scientist at the SETI Institute who leads a Roman coronagraph science team. The instrument will also observe stars encircled by dust or debris clouds, gathering data that could reveal gaps carved by planets scientists can't yet detect and offer fresh insight into whether our solar system's level of clutter is typical. Engineers will collect extensive test data to evaluate how well the technology performs in space and identify any issues to address before similar systems fly again.
Every aspect of Roman's coronagraph will inform future telescopes pursuing ever-smaller planets, including the Habitable Worlds Observatory that NASA hopes to launch perhaps in the 2040s, which will require a coronagraph up to 100 times more effective. A coronagraph with adaptive optics and nearly the same sensitivity as Roman's is also planned for the Lazuli Space Observatory that ex-Google CEO Eric Schmidt's research institution announced in January. According to Julie McEnery, an astrophysicist at NASA's Goddard Space Flight Center and senior project scientist for Roman, demonstrating that the technology works by achieving something scientifically interesting is the best possible outcome. Though imaging alien worlds stands as the most compelling application, coronagraphs could eventually show astronomers binary stars or objects concealed near bright quasars, making Roman a vital first step toward a future where such observations become routine. The engineering lessons from this mission will likely define whether humanity's search for habitable worlds accelerates or stalls for another generation, as space agencies worldwide weigh the considerable cost of building instruments sophisticated enough to match the coronagraph's ambitions.