A giant exoplanet located approximately 1,000 light-years from Earth has stopped transiting its parent star, leaving astronomers without the characteristic drops in starlight recorded over seven years of observation, Space reported.
The planet, designated TOI-2535 b, is classified as a “hot Jupiter” that orbits its star in an 8.25-day cycle. NASA’s Transiting Exoplanet Survey Satellite (TESS) first began examining the system in April 2019, according to Popular Science.
Researchers noticed that the planet’s transits did not follow a regular schedule, arriving up to six hours early or late. Over time, the transits also grew progressively shorter and shallower before failing to appear entirely in 2026, as detailed by researchers including UCLA astronomers.
Scientists determined that the strange orbital behavior stems from an invisible second planet in the system. The two bodies pull on each other gravitationally, causing their orbits to tilt and wobble like a pair of tops, as reported by Ars Technica.
Samuel Yee, a 51 Pegasi b Postdoctoral Fellow at UCLA and the study’s corresponding author, explained in a profile published by Popular Science that “We think of the universe as resembling clockwork, where everything is regular, but that’s not true.” Yee also said that “If there are multiple planets in a system, they can affect each other’s orbits.”
This extreme tilting pushed TOI-2535 b out of alignment with Earth’s line of sight to the star. The research team published their findings on Monday, November 9, in the Astrophysical Journal Letters.
To understand how such rapid changes could occur, researchers modeled 300,000 different starting configurations. They found that the system remains stable over short periods as long as the planets maintain an orbital resonance, according to Ars Technica.
Running the top 100 solutions forward for a million years revealed that about two-thirds of the configurations became unstable. The surviving third indicated that the hidden neighbor must be at least Saturn-sized, and the mutual angle between their orbits must remain relatively small to prevent a close, disruptive approach. The second, unseen planet “would need to be either extremely massive or on a highly eccentric orbit,” the researchers said.
Yee told UCLA Newsroom that “This is the most extreme example we’ve seen because the two planets are interacting so strongly. The planet’s orbit is tilting so quickly that its transit disappeared while we were watching.”
The mechanics behind the disappearing planet mirror the geometry that makes eclipses on Earth infrequent. UCLA astrophysicist and co-author Erik Petigura said that if the moon’s orbit were perfectly aligned with Earth’s path around the sun, an eclipse would occur every month, as reported by UCLA Newsroom.
Petigura explained that “If the moon’s orbit around the Earth was perfectly aligned with the Earth’s orbit around the sun, we would see an eclipse every month,” adding that “But because the moon’s orbit is tilted, eclipses are less common.”
Calculations indicate that TOI-2535 b will not cross the face of its star again for another 30 to 50 years, though the hidden companion might emerge sooner, according to Popular Science.
Yee told Space that “Because TOI-2535 b has a close neighbor, it probably migrated by slowly spiraling in instead of getting flung in. We may be seeing a formation channel that doesn’t happen very often but is very interesting.”
