Hidden Planet Tilted a Hot Jupiter Out of View of NASA’s TESS
Astronomers say hot Jupiter TOI-2535 b stopped crossing its star after an unseen planet tilted its orbit. The study is in Astrophysical Journal Letters.
A gas giant about 1,000 light-years away, TOI-2535 b, stopped passing in front of its star after seven years of observations, and astronomers now think a second, unseen planet tugged it out of line. The planet is still there, according to a study published Monday (Nov. 9) in the Astrophysical Journal Letters, as reported by Space.com.
The finding shows two planets pulling on each other so strongly that the orbit of one tilted within the span of the observations. It also bears on a long-running question about how giant planets end up so close to their stars.
How a planet slipped out of TESS’s view
NASA’s Transiting Exoplanet Survey Satellite (TESS) monitored TOI-2535 b between April 2019 and March 2026. The planet circles its star every 8.25 Earth days, about 10 times faster than Mercury orbits the sun. Planets that are this large and this hot are called hot Jupiters.
TESS finds such worlds by watching for small, repeating dips in a star’s light. Each dip happens when a planet crosses, or transits, the face of the star. For TOI-2535 b, the dips did not keep a steady schedule. The planet often showed up six hours early or six hours late. Then in March of this year, the dips were gone.
The research team used TESS data to conclude that an unseen neighbor is pulling on TOI-2535 b while the planet pulls back on it. Both orbits wobble as a result. The wobble tilted TOI-2535 b out of alignment with its star, so its path no longer crosses the star’s face from our point of view.
Team member Samuel Yee of the University of California, Los Angeles, said in a statement that planets in a multi-planet system can affect each other’s orbits and that a few such systems are known. “This is the most extreme example we’ve seen,” he said, because the two planets interact so strongly that the transit vanished while astronomers watched.
What happens next for TOI-2535 b
TOI-2535 b is not expected to transit its star again for at least 30 years. The hidden neighbor could cross the star’s face sooner than that, which would give astronomers a direct look at it. The team will now study what the extreme wobble reveals about how the system formed.
Why it matters: how hot Jupiters get close to their stars
Hot Jupiters have puzzled astronomers because current ideas of planet formation say giant planets need a lot of ice to grow, and ice is unlikely to be plentiful as near to a star as TOI-2535 b now sits. That points to a birth far from the star followed by a move inward. Space.com describes two possible routes.
- In the violent route, a near-collision with another planetary object throws the planet onto an elliptical orbit, and interactions with the star then pull it inward.
- In the gentle route, the planet moves inward along with other planets while still inside the flattened cloud of gas and dust around a young star, called a protoplanetary disk.
The gentle route should leave a flat system, with no extreme tilts between planetary orbits. TOI-2535 b is tilting sharply, which seems to rule that route out. But the tilt caused by its neighbor suggests a flat system can be twisted into more tilted orbits later in its life. That leaves slow migration possible even with the tilt.
Because the planet has a close neighbor, Yee said it probably spiraled in slowly instead of being flung in. “We may be seeing a formation channel that doesn’t happen very often,” he said, and he called it very interesting.
What is still unknown
The second planet has not been seen directly. Its presence is inferred from the timing changes and the tilt of TOI-2535 b’s orbit. Whether this path is common among hot Jupiters is also open, since Yee described the channel as one that may not happen very often.
Source: Space.com
