TOI-2535 b\u2019s transits became shorter and shallower before disappearing from TESS observations in 2026.Large timing shifts and changing transit geometry point to an inclined planetary companion pulling on its orbit.Several orbital arrangements remain possible, making further measurements essential to identifying the unseen neighbor.<\/p>\n
A giant planet about 1,000 light-years away has stopped crossing the face of its star from Earth\u2019s 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.<\/p>\n
Researchers led by Samuel Yee and Erik Petigura at UCLA<\/a> describe the discovery in The Astrophysical Journal Letters<\/a>. 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.<\/p>\n 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.<\/p>\n 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>. A nearby companion that strongly perturbs one adds another clue about how such unusual systems develop and move inward.<\/p>\n An artist\u2019s impression of the 10 hot Jupiter exoplanets studied using the Hubble and Spitzer space telescopes. Top row, from left: WASP-12b, WASP-6b, WASP-31b, WASP-39b and HD 189733. Bottom row, from left: HAT-P-12b, WASP-17b, WASP-19b, HAT-P-1b and HD 209458b. (CREDIT: UCLA) How TOI-2535 b disappeared from the transit record<\/p>\n NASA\u2019s 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\u2019s brightness. A transit appears as a small dip when the planet blocks part of the stellar disk.<\/p>\n 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\u2019s edge, shorten the crossing and eventually remove it altogether. A missing transit therefore need not mean a missing planet.<\/p>\n 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.<\/p>\n Other TESS discoveries<\/a> demonstrate how brightness measurements reveal unfamiliar worlds. Studies of irregular transits<\/a> also show that departures from a regular schedule can carry information about planets that are not themselves seen crossing the star.<\/p>\n A wobbling orbit explains the changing view<\/p>\n 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.<\/p>\n<\/p>\n \u201cThis is the most extreme example we\u2019ve seen because the two planets are interacting so strongly,\u201d Yee said. \u201cThe planet\u2019s orbit is tilting so quickly that its transit disappeared while we were watching.\u201d The paper identifies it as the first planet directly observed to cease transiting through this process around a single star.<\/p>\n 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<\/a> provides useful comparisons without making every changing transit the same phenomenon.<\/p>\n The modeled precession timescales are about 30 to 50 years. UCLA\u2019s announcement suggests the planet\u2019s transits may return on roughly that horizon, but the system\u2019s architecture remains uncertain. Future observations could refine the forecast. Its hot Jupiter<\/a> classification describes the world itself, not whether a transit happens to be visible today.<\/p>\n The unseen companion is not fully identified<\/p>\n 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\u2019s motion. These radial-velocity observations detect gravitational tugs through shifts in its spectrum, providing a way to investigate planets even when transits are unavailable.<\/p>\n Comparable work using radial velocities<\/a> 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.<\/p>\n Schematic showing definition of angles used. \u03a9inv is the longitude of ascending node measured in the invariable plane, with the reference direction chosen to be along the intersection between the sky and invariable planes. (CREDIT: Samuel Yee et al, The Astrophysical Journal Letters 2026) <\/p>\n 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.<\/p>\n 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<\/a> around other hot Jupiters make such architectures interesting, while reinforcing the need to measure each system rather than assume they share one history.<\/p>\n A rare clue to how hot Jupiters migrated<\/p>\n 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.<\/p>\n Another route involves migration through the young system\u2019s 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.<\/p>\n \u201cBecause TOI-2535 b has a close neighbor, it probably migrated by slowly spiraling in instead of getting flung in,\u201d Yee said. That interpretation connects the discovery to broader research into planetary migration<\/a>, while remaining dependent on the companion\u2019s eventual characterization.<\/p>\n SOAR HRCam observation of TOI-2535. The black line shows the detection limits as a function of separation, while the inset image shows the speckle autocorrelation function (ACF). (CREDIT: Samuel Yee et al, The Astrophysical Journal Letters 2026) <\/p>\n 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<\/a> help researchers investigate those possibilities, but the present study does not reconstruct one confirmed sequence of formation events.<\/p>\n Practical implications for exoplanet research<\/p>\n 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.<\/p>\n 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.<\/p>\n