TESS sees TOI-2535 b’s transits disappear after seven years
Researchers say a changing orbital alignment moved the planet out of view against its star. Their model suggests that a neighboring giant planet is pulling on its orbit.
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NASA’s TESS mission observed TOI-2535 b pass in front of its star over seven years before those crossings, known as transits, disappeared. Their timing and shape changed gradually before the signal vanished.
The researchers say the planet did not disappear. Instead, its orbit appears to have tilted enough that its path no longer crosses the visible disk of the star from Earth’s point of view. Their model points to the gravitational pull of a proposed neighboring planet, likely at least as massive as Saturn.
TOI-2535 b is a hot Jupiter—a giant planet with a short orbit close to its star—about 1,000 light-years away. The authors say it is the first confirmed planet orbiting a single star whose transits have been directly observed to disappear.
Analysis
A changing view of the orbit
A transit is visible only when a planet’s orbit lines up closely enough with the observer’s view. A small change in the orbit’s tilt can move the planet’s apparent path across the star and eventually beyond its edge. The researchers used changes in transit duration—how long each crossing took—as part of their analysis.
The authors say the system has the largest transit-duration variations and inclination change observed for a planet orbiting a single star, with a precession period of decades. Universe Today reports that its transit-timing variations are among the largest detected and the largest detected for a hot Jupiter.
The single-star distinction matters: planets orbiting two stars can have rapidly changing transit paths and may cross both, one or neither star at different times. The authors say such changes in orbital tilt are generally less dramatic and relatively rare around single stars.
The research, titled “A TESS Disappearing Act: The Vanishing Transits of TOI-2535 b,” was published in The Astrophysical Journal Letters, Universe Today said. Its corresponding author is Samuel Yee, a postdoctoral fellow at UCLA.
Analysis
What a neighboring planet could explain
The proposed neighbor’s mass and orbit come from the researchers’ model. They also infer that it is likely in a mean-motion resonance with TOI-2535 b, meaning the planets’ orbital periods follow a regular numerical relationship.
Yee said a close neighbor would favor a slow inward migration over a scenario in which the planet was flung inward. The authors argue that such systems could not have formed through high-eccentricity migration. But the authors say the disk of material in which planets form would also have reduced their orbital tilts, so a later disturbance would be needed to explain the tilt inferred from the transits. A more accurate picture of the system’s orbits is needed to assess other formation explanations.
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