A Hot Jupiter Vanished From View After Seven Years. A Hidden Planet Did It

A giant planet that astronomers had tracked for seven years has dropped out of sight, and a new study says the cause is a second, unseen planet pulling it off course. The world, called TOI-2535 b, is about 1,000 light-years away. According to Space.com, it did not disappear. Its orbit tilted so quickly that it no longer passes in front of its star.

The research was published Monday, Nov. 9, in the Astrophysical Journal Letters.

How a planet slipped out of view

NASA's Transiting Exoplanet Survey Satellite, known as TESS, observed TOI-2535 b between April 2019 and March 2026. The planet circles its star every 8.25 Earth days. Space.com reported that this is 10 times quicker than Mercury's orbit around the sun, which makes the planet a so-called hot Jupiter: a gas giant that is blisteringly hot because it sits so close to its star.

TESS finds planets by watching for small dips in starlight. Each time a planet crosses, or transits, the face of its star, the star briefly dims. For TOI-2535 b, those dips did not arrive on a steady schedule. The planet often showed up six hours early or six hours late. Then, in March this year, the dips stopped altogether.

What the astronomers found

The research team used TESS data to show that TOI-2535 b is being tugged by an unseen neighbor, and that it tugs back. The pull makes the orbits of both worlds wobble. The planet vanished from view when that wobble tilted its path out of line with the star, as seen from Earth.

Samuel Yee of the University of California, Los Angeles, a member of the team, said in a statement that people often imagine the universe as clockwork, but planets in the same system can affect one another's orbits. He said astronomers know of a few systems like this, yet TOI-2535 is the most extreme example seen so far because the two planets interact so strongly. The tilt changed fast enough, he said, that the transit disappeared while the team was watching.

The hidden planet has not been seen directly. Space.com reported that TOI-2535 b is not expected to cross its star again for at least 30 years, though the neighbor tugging on it may cross the star sooner than that.

Why it matters: a clue to how hot Jupiters form

Hot Jupiters are puzzling. Current ideas about planet formation suggest that gas giants like this one need to build up around a great deal of ice, and ice is unlikely to be plentiful so close to a star. That points to the planets forming far from their stars and then moving inward. Space.com described two ways this could happen.

A violent event, such as a near-collision with another planetary object, throws the planet into an elliptical orbit, and interactions with the star then pull it inward.
The planet drifts inward, along with other planets, within the flattened cloud of gas and dust around a young star, called a protoplanetary disk.

The second, calmer route should leave a very flat system, with no extreme tilts between the orbits of its planets. TOI-2535 does have a strong tilt, but the new finding suggests that a flat system can be twisted into more tilted orbits later in its life. That keeps the slow-migration route possible even in a system like this one.

Yee said that because TOI-2535 b has a close neighbor, it probably spiraled in slowly rather than being flung inward. He added that the team may be seeing a way of forming such planets that does not happen very often but is very interesting.

What scientists will do next

In the meantime, researchers plan to try to work out what this extremely wobbling system can reveal about how it formed. For readers, the result is a reminder that the orbits of distant planets are not always as regular as they seem, and that a planet can vanish from view without going anywhere. As with any single study, the explanation rests on the team's analysis of the TESS observations, and the hidden planet itself has yet to be spotted.

Around Prague, based on reporting by Space.com

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