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| An artist's illustration showing an exoplanet and two stars. |
Astronomers have uncovered the explanation behind a remarkable cosmic mystery involving TOI-2535 b, a giant exoplanet located approximately 1,000 light-years from Earth. After years of observations, the planet appeared to disappear from the view of NASA's Transiting Exoplanet Survey Satellite (TESS). However, new research suggests that the planet never actually vanished. Instead, the gravitational influence of an unseen neighboring planet gradually changed its orbital alignment, preventing astronomers from detecting its passage in front of its host star.
The findings, published on November 9, 2026, in The Astrophysical Journal Letters, describe the first confirmed case of a planet orbiting a single star whose transits were observed disappearing over time. The discovery offers an unusual opportunity to study planetary gravitational interactions as they happen and could provide important clues about how giant planets migrate through distant solar systems.
NASA's TESS Telescope Watched an Exoplanet Disappear
TOI-2535 b belongs to a category of exoplanets known as hot Jupiters. These massive gaseous worlds resemble Jupiter in size but orbit much closer to their host stars, exposing them to intense stellar radiation. TOI-2535 b completes one orbit every 8.25 days, considerably faster than Mercury, which requires approximately 88 days to circle the Sun. Its short orbital period initially made it a promising target for repeated observations by NASA's planet-hunting telescope.
Between April 2019 and March 2026, TESS repeatedly monitored the TOI-2535 star system. The telescope searches for exoplanets by measuring tiny decreases in stellar brightness when planets pass between their stars and Earth. These events, called transits, provide valuable information about planetary sizes and orbital characteristics. However, researchers noticed that TOI-2535 b was behaving differently from the predictable patterns typically associated with regularly transiting planets.
The planet's transits sometimes occurred as much as six hours earlier or later than expected. More surprisingly, the observed crossings gradually became shorter and shallower, indicating that the planet was passing increasingly close to the visible edge of its star. By March 2026, its transit signal had disappeared entirely from the observations, leaving astronomers with an intriguing question: what could cause a giant planet to disappear without actually leaving its planetary system?
An Unseen Planet Appears to Be Responsible
Researchers led by astronomers at the University of California, Los Angeles, investigated the unusual behavior using TESS observations and precision radial-velocity measurements from the NEID instrument on the WIYN 3.5-meter telescope at Kitt Peak National Observatory. Their analysis points toward an additional planet exerting a powerful gravitational influence on TOI-2535 b. Although this neighboring world has not been directly observed, its gravitational effects provide a compelling explanation for the changing transit times and durations.
According to the researchers' dynamical models, the unseen companion is likely at least as massive as Saturn and occupies a nearby orbit tilted relative to TOI-2535 b's orbital plane. The gravitational interaction causes the planets' orbital planes to undergo a gradual change in orientation known as orbital precession. This movement is comparable to the wobbling motion of a spinning top, with the planets continuously influencing each other's orbital trajectories.
Why the Planet Is No Longer Visible to TESS
Detecting an exoplanet through the transit method requires an exceptionally precise alignment between the planet, its host star, and the observer. Even a relatively small change in orbital inclination can cause a planet to stop crossing the star's visible disk from Earth's perspective. In the case of TOI-2535 b, the gravitational influence of its suspected companion gradually shifted the planet's transit path until it no longer crossed the star from our viewpoint.
This distinction is important because the planet itself has not disappeared or been destroyed. It continues orbiting its star, but its changing geometry makes it temporarily undetectable through the transit technique. The research demonstrates how interactions between massive planets can alter what astronomers observe over surprisingly short periods, rather than only across millions of years.
What the Discovery Reveals About Hot Jupiter Formation
Beyond explaining the missing transit signals, the study raises important questions about how hot Jupiters reach their unusually close orbits. According to current planetary formation models, giant gaseous planets are generally expected to form farther from their stars, where colder temperatures allow the accumulation of substantial amounts of solid material. Scientists have therefore proposed several mechanisms that could move these planets inward after their formation.
One possibility involves violent gravitational encounters that push a giant planet into a highly elongated orbit before interactions with its star gradually bring it closer. Another involves smoother migration through the gas-rich protoplanetary disk surrounding a young star. The suspected massive companion near TOI-2535 b makes the second explanation particularly interesting, since nearby giant planets may survive a gradual migration process together.
However, the system also presents a complication. Disk-driven migration would generally be expected to produce relatively well-aligned planetary orbits, while the observed behavior suggests that the planets' orbital planes are noticeably tilted relative to each other. This could indicate that additional gravitational interactions altered the system after its initial formation. The precise sequence of events remains uncertain, making TOI-2535 an especially valuable system for testing theories of planetary evolution.
The discovery also connects with broader research into the environments where planets form. For example, earlier observations of a chaotic protoplanetary disk surrounding a young star highlight how complex these planetary birthplaces can be. Together, such findings illustrate why understanding a planet's present-day orbit often requires investigating the conditions and gravitational interactions that shaped its history.
Could TOI-2535 b Become Visible Again?
Although TOI-2535 b is no longer producing detectable transits, astronomers do not expect its disappearance to be permanent. Based on the proposed orbital dynamics, researchers estimate that the planet could begin crossing its host star again in approximately 30 to 50 years. Its suspected neighboring planet might become detectable through transits sooner, depending on how the orbital orientations evolve.
Future observations, particularly additional radial-velocity measurements, could help establish the companion's mass and orbital characteristics more precisely. Such measurements detect subtle changes in a star's motion caused by the gravitational pull of orbiting planets, allowing researchers to investigate worlds even when they do not transit. Continued monitoring will also help determine whether the proposed orbital model correctly predicts the system's behavior.
NASA's TESS mission has already demonstrated that detailed stellar observations can reveal far more than the presence of planets. Scientists have also used its measurements to study stellar oscillations and investigate unusual stars, including a peculiar star whose apparent age conflicts with its chemical composition. These different applications emphasize the scientific value of collecting precise observations over extended periods.
A Rare Glimpse of Planetary Orbits Changing in Real Time
The disappearance of TOI-2535 b's transit signal represents an important development in exoplanet research because astronomers have directly tracked a dramatic orbital change within a relatively short observational period. Rather than relying entirely on theoretical predictions or snapshots of distant planetary systems, researchers now have evidence of gravitational interactions changing an exoplanet's visibility over just seven years.
The suspected companion still requires further investigation, and questions remain about the system's formation history. Nevertheless, the observations demonstrate that planetary systems are not always the predictable arrangements they initially appear to be. TOI-2535 b may have disappeared from TESS's view, but its unusual behavior has revealed a potentially complex planetary system and opened a new opportunity to understand how giant worlds influence one another.
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| An illustration showing the hot Jupiters observed by the Hubble and Spitzer space telescopes. |