Comprising a super-Earth, a temperate gas giant, and a more substantial brown dwarf, the TOI-201 celestial arrangement exhibits orbital periods of 5.8, 53, and 2,900 days, respectively.
An artist’s impression of the warm giant exoplanet TOI-201b and its parent star. Image credit: Sci.News.
TOI-201 denotes a luminous F-type star situated 372 light-years distant within the Pictor constellation.
This stellar body surpasses the Sun in both size and mass by 32%, with an estimated age of approximately 870 million years.
Known also by the designations HD 39474 and TIC 350618622, it is orbited by no fewer than three celestial bodies: TOI-201b, c, and d.
“Our objective was to meticulously characterize the TOI-201 planetary system to gain insight not only into the identities of its constituents but also into their dynamic interplay,” stated Ismael Mireles, a doctoral candidate at the University of New Mexico.
“Such investigations equip scientists with a deeper comprehension of the formation and evolutionary trajectories of planetary systems akin to our own Solar System.”
TOI-201d is identified as a terrestrial super-Earth planet, approximately 1.4 times the diameter of Earth and possessing a mass roughly six times that of our planet, completing a full revolution in 5.8 days.
TOI-201b is classified as a temperate Jupiter-analog exoplanet, possessing about half the mass of Jupiter and completing an orbit every 53 days.
TOI-201c is a brown dwarf – the most massive entity within the system aside from the parent star – traversing a vast, highly eccentric orbit that spans approximately 8 years. Its gravitational influence is predominantly responsible for the system’s observed dynamic behavior. Furthermore, TOI-201c stands as the longest-period transiting object ever documented.
“TOI-201c presents a unique case due to its exceptionally protracted orbital period (approximately 7.9 years) and its position within a system containing two inner planets,” Mireles remarked.
“The majority of recognized transiting brown dwarfs maintain orbits significantly closer to their host stars.”
“Given that the mass of TOI-201c hovers near the threshold distinguishing massive planets from brown dwarfs, one intriguing enigma presented by this system is whether this celestial body originated as a planet or as a star,” commented Professor Diana Dragomir of the University of New Mexico.
“This represents one of merely a handful of systems where planetary orbital shifts can be actively observed unfolding on human timescales,” Mireles elaborated.
“It provides an exceptional, direct vantage point into the dynamic evolution of planetary systems. Indeed, within a span of 200 years, only two of the three identified objects will continue to exhibit transits.”
What renders the TOI-201 system particularly noteworthy is the astronomers’ unprecedented ability to witness its transformations in real-time.
“The orbital paths of these planets are mutually inclined, and as a consequence, they are gradually inducing alterations in each other’s orientations,” Mireles explained.
“This finding was unexpected, as planetary bodies are typically anticipated to possess aligned orbits, mirroring the arrangement within the Solar System, if they formed within the plane of the protoplanetary disk present during the star’s early stages,” Professor Dragomir noted.
“Consequently, the pivotal question now for TOI-201 is to ascertain the mechanism by which these three bodies acquired such distinctly tilted orbital configurations.”
Within two centuries, TOI-201d will cease to transit; several hundred years thereafter, TOI-201b will similarly stop transiting, followed eventually by TOI-201c’s cessation of transiting.
However, these celestial bodies will recommence their transiting phases millennia from now, as they undergo cyclical periods of transit and non-transit configurations.
The subsequent predicted transit of TOI-201c is scheduled for March 26, 2031, presenting a rare opportunity for synchronized follow-up observations globally, including participation by citizen scientists.
“The comprehensive study of this system was truly a multi-year endeavor involving a large collaborative team effort,” Mireles attested.
A research publication detailing these discoveries has been issued in the esteemed journal Science Advances.
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Ismael Mireles et al. 2026. Uncovering the rapidly evolving orbits of the dynamic TOI-201 system. Science Advances 12 (16); doi: 10.1126/sciadv.aef2618
