TOI-2535 b: the exoplanet that vanished from TESS, and why

NASA's TESS space telescope tracked the planet from April 2019 to March this year. TESS finds planets by spotting tiny drops in a star's brightness. When a planet crosses in front of its star, it blocks a little light. That event is called a transit.

Why did TOI-2535 b disappear from TESS?

The transits began to misbehave. They arrived up to six hours early or late compared with a regular orbit. They also grew shorter and weaker, until in March the signal was gone.

A team led by researchers at the University of California, Los Angeles worked out the cause: another planet is pulling on TOI-2535 b. That second world has not shown up in transit observations so far, but its gravity clearly leaves a mark.

The two planets disturb each other's orbits. Their orbital planes slowly change tilt and wobble, a bit like a spinning top. For TOI-2535 b the tilt became large enough that, from Earth, it no longer passes directly in front of its star.

Will we see it transit again?

Not soon. The planet still exists and still orbits its star, but its path is now at an angle where telescopes cannot catch the brightness dips. Astronomers do not expect another transit for at least 30 years, and the estimate is 30 to 50 years.

The hidden companion may be the one to show itself first. It could cross in front of the star much sooner.