NASA’s TESS Mission Finds a Planetary System in a New Way
Featured image: Artist’s concept of a super-Jupiter orbiting an orange dwarf star; credit: NASA
NASA’s Transiting Exoplanet Survey Satellite has discovered its first exoplanet using gravitational microlensing, a technique the mission was never designed to perform. The planet, designated Gaia23bra b, is a super-Jupiter with 1.6 times the mass of Jupiter orbiting an orange dwarf star roughly 80 percent the mass of the Sun at a distance comparable to Jupiter’s orbit around our own star. It lies approximately 40,000 light-years away, far beyond TESS’s typical detection range of roughly 150 light-years.
“When TESS launched, no one expected it to ever be capable of finding this kind of planet,” said Diana Dragomir of the University of New Mexico.
The discovery, published July 1 in the Astrophysical Journal Letters, began with a brightening alert from ESA’s Gaia space telescope in 2023. TESS’s archived data later confirmed the microlensing signature that Gaia’s sparse observations had missed. Lead author Mallory Harris, a Ph.D. candidate at the University of New Mexico, led the analysis that connected the two datasets.
Gravitational microlensing occurs when two stars align from Earth’s perspective. The foreground star’s gravity warps space-time, magnifying the background star’s light like a natural lens. If a planet orbits the foreground star, it creates its own tiny perturbation, producing a brief brightness deviation that reveals the planet’s mass and orbital distance. Unlike the transit method, which repeats predictably, microlensing is a one-time event.
“We will probably find the first Earth analog with microlensing, and then wave at it as it goes by because we will never see it again,” Harris said.
The discovery opens a new frontier for TESS. The mission was designed for the transit method, watching stars dim periodically as planets pass in front. Microlensing complements this by finding planets at greater orbital distances, the kind that resemble our own solar system’s architecture, rather than the close-in worlds that transits detect best. TESS’s wide-field, rapid-cadence observations across the galactic plane are well suited to catching microlensing events in regions of the galaxy that experience less radiation and fewer supernovae, potentially offering more favorable conditions for planetary habitability than the crowded galactic center.
The finding also previews the scientific potential of the Nancy Grace Roman Space Telescope, scheduled for launch on Aug. 30, 2026. Roman will conduct a dedicated microlensing survey of the galactic bulge, expected to discover roughly 1,000 microlensing planets and about 100,000 transiting planets. The TESS discovery demonstrates that Roman’s data will be rich with microlensing signatures.
Harris and the team suspect many more microlensing planets are already hiding in TESS data, waiting for the right alignment of archival searches and alert networks to be found.