A hidden giant planet may explain TOI-2535 b’s strange disappearing act

A giant planet about 1,000 light-years away has stopped crossing the face of its star from Earth’s viewpoint. Astronomers watched its transits change over seven years before the familiar dips in starlight disappeared. The planet itself remains in orbit. What changed was the alignment that allowed telescopes to detect those crossings.

Researchers led by Samuel Yee and Erik Petigura at UCLA describe the discovery in The Astrophysical Journal Letters. Their subject, TOI-2535 b, is a Jupiter-sized planet orbiting its star every 8.236 days. Its behavior makes it an unusual example of interacting planets.

The observations point to another planet whose gravity makes the orbit wobble. Researchers also measured transits arriving as much as six hours early or late compared with a regular schedule. Together, the timing and shape changes reveal a system whose movements are far less predictable than a simple planetary clock.

TOI-2535 b belongs to the class called hot Jupiters, gas giants found close to their stars. These worlds already challenge simple accounts of planet formation. A nearby companion that strongly perturbs one adds another clue about how such unusual systems develop and move inward.

NASA’s Transiting Exoplanet Survey Satellite, or TESS, observed the system in five sectors between April 2019 and March 2026. Rather than photographing the planet directly, it measured the star’s brightness. A transit appears as a small dip when the planet blocks part of the stellar disk.

That technique requires precise geometry. A planet may orbit normally without ever crossing its star along our line of sight. Changing the orbital plane can move a previously visible transit toward the star’s edge, shorten the crossing and eventually remove it altogether. A missing transit therefore need not mean a missing planet.

The earlier observations showed progressively changing transit shapes. By the final TESS observations, no clear events remained. Researchers searched across possible timing offsets and tested whether inserted artificial transits could be recovered. These checks helped distinguish a genuinely weakened or absent transit from one simply arriving at an unexpected time.

Other TESS discoveries demonstrate how brightness measurements reveal unfamiliar worlds. Studies of irregular transits also show that departures from a regular schedule can carry information about planets that are not themselves seen crossing the star.

The proposed mechanism is nodal precession: the orientation of an orbit changes, rather like the axis of a spinning top tracing a circle. Gravity from an inclined companion can drive that motion. The planet continues circling its star while the path it traces across the sky shifts relative to Earth.

“This is the most extreme example we’ve seen because the two planets are interacting so strongly,” Yee said. “The planet’s orbit is tilting so quickly that its transit disappeared while we were watching.” The paper identifies it as the first planet directly observed to cease transiting through this process around a single star.

That qualification matters. Planets orbiting two stars can show dramatic transit changes because their orbital geometry evolves and the stars themselves move. TOI-2535 b demonstrates an especially rapid change around one star. Other research on orbital interactions provides useful comparisons without making every changing transit the same phenomenon.

The modeled precession timescales are about 30 to 50 years. UCLA’s announcement suggests the planet’s transits may return on roughly that horizon, but the system’s architecture remains uncertain. Future observations could refine the forecast. Its hot Jupiter classification describes the world itself, not whether a transit happens to be visible today.

The team combined space-based observations with ground-based follow-up. The NEID spectrograph on the WIYN 3.5-meter telescope measured changes in the star’s motion. These radial-velocity observations detect gravitational tugs through shifts in its spectrum, providing a way to investigate planets even when transits are unavailable.

Comparable work using radial velocities shows how the method complements transit measurements. In this system, follow-up also helped rule out explanations involving an eclipsing stellar companion or an unrelated nearby source. The researchers established the transiting object as a planet before exploring the perturbations.

Their simulations did not identify one unique solution for the neighboring planet. Long-term stability tests favored arrangements near 2:1 or 3:2 orbital resonances, where orbital periods have simple numerical relationships. Viable models generally favored a giant companion, but its precise mass, location and mutual inclination remain uncertain.

Residual timing and velocity scatter leaves open the possibility of more than one unseen planet. This is not a fully solved two-world portrait. Discoveries of nearby companions around other hot Jupiters make such architectures interesting, while reinforcing the need to measure each system rather than assume they share one history.

Gas giants are generally thought to form farther from their stars than the tight orbits occupied by hot Jupiters. Researchers therefore investigate ways they could move inward. One route involves a highly elongated orbit, followed by tidal interactions that gradually shrink and circularize it close to the star.

Another route involves migration through the young system’s gas disk. The planet exchanges angular momentum with the surrounding material and drifts inward. A close planetary companion is easier to preserve through this process than through a highly disruptive migration history. Resonant configurations can also develop as migrating planets interact.

“Because TOI-2535 b has a close neighbor, it probably migrated by slowly spiraling in instead of getting flung in,” Yee said. That interpretation connects the discovery to broader research into planetary migration, while remaining dependent on the companion’s eventual characterization.

There is still a puzzle: a gas disk normally damps orbital tilts. Some later interaction may have increased the mutual inclination, perhaps through resonant evolution rather than a literal collision. Systems with unusual orbital motion help researchers investigate those possibilities, but the present study does not reconstruct one confirmed sequence of formation events.

The immediate priority is a more densely sampled radial-velocity campaign. With the planet no longer providing regular transit measurements, stellar-motion data offer the best route to locating its companion. Better constraints would help distinguish the viable orbital models and test whether additional bodies contribute to the remaining unexplained signals.

The discovery also demonstrates the value of returning to the same stars. The authors report that four years of TESS data alone would not have securely established the transit-duration changes. A longer baseline revealed the trajectory. Continued surveys can therefore uncover dynamics that a shorter observing program would miss.

Changing transit geometry affects opportunities to characterize planets, including measurements of their atmospheres. It also reminds astronomers that the planets detected in a system depend partly on viewing angle. A world that does not transit can still strongly influence a visible neighbor.

TOI-2535 b’s disappearing signal turns an observational loss into evidence about a hidden system. Its future study will combine planet detection methods rather than rely on a single recurring shadow. The planet has not vanished, but its changing alignment has exposed a gravitational story that would otherwise remain difficult to see.

These resources examine orbital precession, resonant planets and possible hot Jupiter migration pathways, listed newest first.

Time’s running out to catch giant planet’s strange orbit
Researchers describe TOI-1355 b, another giant planet predicted to leave a transiting configuration as its orbit evolves. (University of Tokyo, September 2026)

Photodynamical analysis of the TOI-4504 system
Orbital precession brings a previously nontransiting planet into view, revealing a resonant planetary arrangement. (Astronomy & Astrophysics, July 2026)

Discovery of a cold giant planet and mass measurement of a hot super-Earth in the multi-planetary system WASP-132
A hot Jupiter with inner and outer companions provides evidence relevant to less disruptive migration histories. (Astronomy & Astrophysics, January 2025)

A hot-Jupiter progenitor on a super-eccentric retrograde orbit
Observations of an extremely elongated orbit explore a possible high-eccentricity route toward hot Jupiter formation. (Nature, July 2024)

Transit Depth Variations Reveal TOI-216 b to be a Super-Puff
The authors’ preprint describes a shift from grazing to full transits that enabled a better planetary-radius measurement. (arXiv preprint, December 2022)

Research findings are available online in The Astrophysical Journal Letters.

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