In the coming years, NASA's Nancy Grace Roman Space Telescope will peer toward the galactic center and fundamentally reshape what we know about worlds beyond our own solar system. The mission is expected to reveal approximately 100,000 exoplanets—a staggering leap compared to the 6,300 discovered so far—mostly in regions of the galaxy that remain virtually unexplored.
This matters because planet formation may look dramatically different depending on where in the Milky Way you look. Our solar system sits about 27,000 light-years from the galactic center, nestled roughly halfway out on one of the galaxy's spiral arms. A Kepler Space Telescope study revealed that stars on the fringes of the Milky Way possess fewer of the most common planet types detected so far. Roman will search in the opposite direction, toward the densely packed galactic center, and could uncover entirely different planetary architectures in that neighborhood.
"Our galaxy is home to a variety of different environments, but when it comes to hunting for exoplanets, we've really only explored one: our own neighborhood," said Elisa Quintana, an exoplanet researcher at NASA's Goddard Space Flight Center in Greenbelt, Maryland. Quintana leads a team building software and simulations to prepare for Roman's observations. "Roman will extend the search far enough to encompass other galactic habitats, which could help us learn how planet formation varies across different regions of the Milky Way."
Roman will employ two complementary detection methods to map the galactic landscape. The transit method—which will reveal around 100,000 worlds—works by catching planets as they cross in front of their host stars, temporarily dimming the starlight. This technique excels at finding gigantic, scorching worlds, since they block the most starlight and transit more frequently. The second method, microlensing, relies on gravity itself. When an intervening star and its orbiting planets magnify the light of a farther star, they create a characteristic brightening that reveals planetary systems almost undetectable by other means. Roman will use microlensing to discover more than 1,000 additional worlds, particularly excelling at finding planets with larger orbits—like those in our solar system—and Earth- and Mars-sized worlds nestled in or beyond their star's habitable zone.
The galactic bulge survey, one of Roman's core missions, will monitor stars throughout a deep slice of the galaxy, peering all the way through the densely packed stellar hub at the center to the far side. This region is fundamentally different from Earth's neighborhood. The galactic center is rich in planet-building elements like silicon, oxygen, and magnesium—forged by multiple generations of stars and supernovae—but bathed in intense radiation from densely packed stars, including massive ones that emit enormous amounts of high-energy ultraviolet light and X-rays. The outer regions have milder radiation but fewer planet-building materials. Between them lies what scientists call the galactic habitable zone, a balance point where radiation and elements align more favorably for potentially life-supporting worlds.
By pairing these two detection techniques across such diverse galactic environments, Roman will offer astronomers an unprecedented view of how planets form and evolve throughout the Milky Way. The mission promises to answer questions that have lingered since the first exoplanet discovery: Are Earth-like worlds common? How do planetary systems depend on their galactic neighborhood? What does our own cosmic origin story reveal about worlds forming elsewhere?