A TESS microlensing planet has turned up where the mission was never expected to look. NASA reports that archived TESS data caught Gaia23bra b, a super-Jupiter about 40,000 light-years away, after a brief brightening first flagged by ESA’s Gaia telescope in 2023.
According to NASA, this is the first time TESS has identified a planet through gravitational microlensing rather than a transit. The world is about 1.6 times Jupiter’s mass and orbits an orange dwarf at a Jupiter-like distance. That geometry sits far outside TESS’s usual ~150-light-year transit hunt.
What the TESS microlensing planet signal showed
Microlensing happens when a nearer star briefly magnifies a distant background star. If a planet orbits the nearer star, it can add a short spike in the light curve. Gaia saw the star brighten, yet its sparse sampling missed the planetary wiggle. Meanwhile, TESS was watching the same sky patch with denser timing, so the planet’s fingerprint stood out.
Mallory Harris of the University of New Mexico led the analysis published July 1 in The Astrophysical Journal Letters. Co-author Diana Dragomir notes that nobody expected TESS to find this class of world when it launched. As a result, more TESS microlensing planet candidates may already sit in the archive.
Why distant Jupiter analogs matter
Transits favor large planets hugging their stars. Microlensing instead favors cooler worlds at wider orbits, including habitable-zone and beyond. However, each event happens once. Therefore, the method is better for demographics than for repeat follow-up of a single Earth twin.
Also, the find previews what NASA’s Nancy Grace Roman Space Telescope aims to do at scale when it surveys the galactic bulge. TESS covers other parts of the galactic plane, so it can sample different stellar neighborhoods. For Axo Science readers, the takeaway is method expansion: a transit satellite just proved it can moonlight as a microlensing scout.
Finally, the TESS microlensing planet Gaia23bra b shows that old light curves still hide new solar-system analogs if teams ask a different question of the data.