Astronomers have uncovered a rare Tatooine-like exoplanet orbiting a binary system closer than any previously imaged planet of its kind. This newly identified world orbits its twin parent stars at an unusually short distance yet still completes a year lasting 300 times longer than an Earth year.
The planet, designated HD 143811 AB b, orbits stars HD 143811 A and HD 143811 B and sits 446 light-years away from Earth. This rare exoplanet discovery excites scientists because planets around binary stars are extremely uncommon. With only a handful ever directly imaged, this system provides a valuable opportunity to explore orbital dynamics and planet formation mechanisms in multi-star environments.
According to team member Jason Wang of Northwestern University, only a small portion of the roughly 6,000 known exoplanets orbit binary stars. Even fewer can be directly imaged along with their stellar hosts. Researchers are eager to continue tracking this system to observe how the three bodies move across the sky.
A key insight behind this discovery came from reexamining decade-old data. HD 143811 AB b was uncovered in archival observations captured nearly ten years ago by the Gemini South telescope using the Gemini Planet Imager (GPI). GPI blocked stellar glare with a coronagraph to reveal faint planets and sharpened images with adaptive optics. Operating from 2014 to 2022, the instrument is now being upgraded to GPI 2.0 and will be relocated to the Gemini North telescope.
Researchers decided to reanalyze the old dataset before the upgraded instrument goes online. While expectations were low, the review proved worthwhile. Out of more than 500 stars observed during GPI’s lifetime, only one new planet emerged—HD 143811 AB b—highlighting just how rare exoplanets in such systems truly are.
Nathalie Jones of CIERA analyzed GPI data from 2016 to 2019 and cross-referenced it with W.M. Keck Observatory observations, revealing a faint object moving with its host star. Stars shift position over time, so astronomers revisit objects to determine whether they move in sync. If an object’s motion matches the star’s, it is likely an orbiting planet rather than an unrelated background star.
Further analysis confirmed that HD 143811 AB b is indeed a planet, initially captured in 2016 but missed at the time. A separate team from the University of Exeter arrived at the same conclusion.
Scientists also determined that the planet is enormous—about six times the size of Jupiter—and relatively young at roughly 13 million years old. Although that may seem ancient, it is extremely young on cosmic timescales and still retains heat from its formation.
The planet’s host stars also orbit each other very closely, completing an orbit in just 18 Earth days. However, despite its relatively tight position around the binary, the planet still needs 300 Earth years to complete a single orbit.
Astronomers are not yet certain how such a massive Tatooine-like exoplanet formed in this dynamic environment. With only a few dozen comparable planets known, the available data remains insufficient to construct a complete formation model.
To answer these questions, researchers hope to obtain additional telescope time to continue monitoring the system. Tracking both the binary stars and the planet will allow scientists to better understand their interactions. Jones also plans to continue mining archival data for more hidden planets, hinting that several suspicious objects may await confirmation.
