TESS finds distant super-Jupiter via microlensing — its first planet discovery using the method

NASA says its Transiting Exoplanet Survey Satellite, or TESS, has made its first planet discovery using gravitational microlensing rather than the transit method the mission was built for, uncovering a distant super-Jupiter called Gaia23bra b nearly 40,000 light-years from Earth.

The finding is notable because TESS usually looks for planets around nearby stars by watching for the slight dimming that happens when a planet crosses in front of its star. In this case, NASA said, archival TESS data helped identify a much farther-out planetary system in a completely different way, showing the spacecraft can contribute beyond its original mission.

According to a NASA announcement published Wednesday, the planet is about 1.6 times Jupiter’s mass and orbits an orange dwarf star with about 0.8 times the sun’s mass. NASA said the planet’s orbit is similar in size to Jupiter’s distance from the sun, making it unlike the close-in worlds TESS often finds. The agency said the system lies nearly 40,000 light-years away.

The event was first flagged in 2023 by the European Space Agency’s Gaia mission, whose alert system identified a star that brightened in a way consistent with microlensing. That effect occurs when a foreground star passes in front of a more distant background star and the foreground object’s gravity magnifies the background star’s light. If the foreground star has a planet, the planet can add a brief extra signal to the brightening pattern.

Researchers later checked archival TESS observations and found the spacecraft had been watching the same region of sky during the event. NASA said TESS’s denser time coverage made the difference.

“Gaia’s observations were too sparse to pick up on the planet,” Mallory Harris of the University of New Mexico said via NASA Science. “The TESS spacecraft happened to be monitoring the same area of the sky during the event, and its denser time coverage showed extra features in the light curve caused by a planet.”

NASA said microlensing accounts for less than 5% of known exoplanets. That helps explain why the result stands out: TESS was launched to hunt transiting planets around stars typically within about 150 light-years of Earth, not to help find wide-orbit planets on the far side of the galaxy.

“When TESS launched, no one expected it to ever be capable of finding this kind of planet,” Diana Dragomir of the University of New Mexico said via NASA Science.

NASA announced the result July 1 in a post titled “NASA’s TESS Mission Finds Planetary System in New Way.” The agency said the team’s analysis was published the same day in The Astrophysical Journal Letters. NASA also cast the discovery as a preview of the kind of microlensing work expected from the Nancy Grace Roman Space Telescope, which is designed to use the technique to find many more planets.