NASA Roman Telescope to Discover 100,000 New Planets in 5 Years

NASA's highly anticipated Nancy Grace Roman Space Telescope is on track for a potential fall 2026 launch, with a firm deadline of May 2027. This advanced observatory is projected to achieve a groundbreaking feat within its initial five-year mission: identifying approximately 100,000 new transiting exoplanets. Beyond this, the telescope will also compile the most extensive catalog of rogue, or free-floating, planets ever assembled.

Julie McEnery, Roman's senior project scientist at NASA Goddard, highlighted the mission's immense potential during a December 2025 announcement. "In the mission’s first five years, it’s expected to unveil more than 100,000 distant worlds, hundreds of millions of stars, and billions of galaxies," McEnery stated. The 100,000 figure specifically pertains to transiting planets, celestial bodies that cause a slight dimming of their host star's light as they pass in front of it. This detection method mirrors that employed by the earlier Kepler mission, which confirmed around 2,800 exoplanets in the 2010s. Roman's vastly increased capabilities—a wider survey area, enhanced infrared sensitivity, and deeper views into the Milky Way's dense core—will enable it to discover planets on a scale nearly 100 times greater.

Mapping the Unseen Universe

What truly sets the Roman mission apart is its dual approach to planet detection. Alongside the transit method, Roman will employ gravitational microlensing, a technique predicted by Albert Einstein and refined since the 1980s. This phenomenon leverages the bending of light by mass: when a massive object passes between an observer and a distant star, its gravity focuses the star's light, causing a temporary brightening. Microlensing offers a significant advantage because it can detect planets irrespective of their host star's visibility from Earth, and crucially, it can identify planets that drift through interstellar space entirely on their own. These solitary bodies are known as rogue planets.

While theoretical models have long suggested the existence of rogue planets, and early candidates were identified through ground-based surveys in the 1990s and 2000s by collaborations like OGLE and MOA, Roman aims to transform our understanding of these enigmatic worlds. Observations from the James Webb Space Telescope in 2023 added hundreds more candidates. Roman is not expected to find the first rogue planets but rather to transition the known count from a mere few dozen confirmed cases to a comprehensive population census.

A 2023 study by Naoki Koshimoto of Osaka University and NASA Goddard collaborators analyzed existing microlensing data and simulated Roman's performance. Their projections suggest Roman will detect approximately 400 Earth-mass rogue planets during its primary mission, an eightfold increase over previous estimates. This revised figure implies that low-mass rogue planets are far more common than previously assumed. Roman's advanced capabilities will also allow for the detection of higher-mass rogue planets, including Jupiter- and Neptune-mass objects, and extend detection limits to lower masses than ever before possible from ground-based observatories.

"Roman will be sensitive to even lower-mass rogue planets since it will observe from space," Koshimoto noted in NASA materials. "The combination of Roman’s wide view and sharp vision will allow us to study the objects it finds in more detail than we can do using only ground-based telescopes." The microlensing program, officially designated the Galactic Bulge Time-Domain Survey (GBTDS), will also identify about 1,000 ordinary planets orbiting host stars. These often-missed planets have orbital periods too long for reliable transit detection, making long-baseline microlensing campaigns like Roman's essential for their discovery.

The GBTDS will repeatedly survey six fields near the Milky Way's center, observing hundreds of millions of stars for microlensing events. This region offers the highest density of stars for lensing and the greatest probability of foreground objects passing in front of them. The survey involves six 72-day high-cadence observing seasons, interspersed with four low-cadence periods to capture events of varying durations. This strategy enables the detection of everything from Earth-mass rogue planets with short microlensing signatures to heavier objects producing multi-year events.

The significance of Roman's mission extends beyond simply increasing exoplanet counts. With an estimated exoplanet total of around 6,000 over thirty years, Roman is poised to increase this number by seventeenfold in just five years. More importantly, it will provide the first robust statistical samples of free-floating planets and orbital characteristics. Answering questions about the prevalence of Earth-sized planets in habitable zones, the mass distribution of rogue worlds, and how planetary populations vary across the galaxy, currently based on limited data, will become possible with Roman's statistical power.

Roman is equipped with two instruments: the Wide Field Instrument, responsible for the bulk of the survey work and exoplanet discoveries, and the Coronagraph Instrument. The latter, a technology demonstration, will directly image a small number of exoplanets around nearby stars, testing methods for future missions designed to capture images of Earth-like worlds. The observatory will be positioned at the second Earth-Sun Lagrange point, a million miles from Earth, similar to the James Webb Space Telescope's location.