NASA's Roman Space Telescope will hunt dark matter and Earth-like exoplanets

In 2025, NASA will send a new observatory into space with a mission that reaches toward two of astronomy's deepest questions: What is dark matter, and are we alone? The Nancy Grace Roman Space Telescope will inherit the work of Hubble, the instrument that has defined our view of the cosmos for three decades, but with capabilities that dwarf its predecessor. Where Hubble sees a narrow slice of sky, Roman will capture an area 100 times larger while maintaining the same optical sharpness—a leap in scale that will let astronomers survey 100 million stars and, in doing so, discover roughly 2,500 new worlds beyond our solar system.

The telescope's hunt for exoplanets will focus on a category of worlds that previous missions largely missed. NASA's Kepler and the Transiting Exoplanet Survey Satellite have already found more than 4,000 exoplanets, but most were large gas giants circling dim stars. Roman will reverse that equation, searching specifically for smaller, rocky planets orbiting bright stars—the kind of world that might harbor life as we know it. The technique it will use, called microlensing, exploits a quirk of gravity: when a star passes in front of a distant star, its gravitational field bends and magnifies the light coming from behind it, creating a brightening effect. If that foreground star has planets, their gravity adds to the effect, making them detectable even when they are small and far from their host.

But exoplanet discovery, for all its romance, is only half the telescope's purpose. The other half addresses a mystery so profound that it reframes what we think the universe actually is. Dark matter—the invisible substance that makes up roughly 27 percent of all mass in the cosmos—has never been directly observed. We know it exists because we can measure its gravitational effects on galaxies and light, but its nature remains unknown. Normal matter, the atoms and molecules that form stars, planets, and us, accounts for only about five percent of the universe's total mass. The rest is dark matter and dark energy, a still more enigmatic force that appears to be accelerating the universe's expansion.

Roman will not try to observe dark matter directly. Instead, it will map how the distribution of galaxies and dark matter has shifted over billions of years of cosmic history. By studying ancient supernovae—the deaths of stars that occurred in the distant past—the telescope will create a timeline of how the universe has evolved. Because dark energy may be driving the universe's expansion, understanding how the cosmos has changed over time offers a window into understanding this strange force. The telescope's surface has been figured to a precision hundreds of times finer than a household mirror, enabling it to detect the faintest signals from the most distant objects.

The instrument is named for Nancy Grace Roman, who died in 2018 at age 93. Roman was NASA's first chief astronomer and the first woman to hold an executive position at the agency. In the 1960s, she assembled a committee of astronomers and engineers to develop space telescopes, work that directly led to Hubble's creation. She became known as the Mother of Hubble, and her legacy shaped the trajectory of space-based astronomy for generations. When NASA renamed the telescope in her honor in 2020—it had previously been called the Wide Field Infrared Space Telescope—the agency acknowledged both her pioneering role in the field and her role in opening doors for women in astronomy.

Roman's primary mission is designed to last five years, with the possibility of extension for another five. It arrives at a moment of transition. Hubble, which launched in 1990, was initially scheduled to retire this year but has been granted a reprieve until 2025, when Roman launches. The James Webb Space Telescope, which began observations in late 2021, will operate alongside Roman, each instrument bringing different capabilities to bear on the universe's deepest questions. Together, these observatories represent the next chapter in humanity's effort to see farther, deeper, and with greater precision than ever before—to find worlds that might be home to life, and to understand the invisible architecture that holds the universe together.