Exomoons may be missing from planet data

When a planet crosses in front of its star, it blocks some of the starlight. The Kepler telescope used these small drops in brightness to find thousands of exoplanets. A moon is smaller than its planet and may cross before or after it. The moon’s dip can be so faint that software classifies it as noise. The moon also pulls the planet around the pair’s shared centre of mass. As a result, the planet’s transit can happen a few minutes early or late.

In 2018, David Kipping’s astronomy team studied the transits of Kepler-1625b. They saw an extra dip and a shift in timing, then named the candidate Kepler-1625b-i. A later Hubble observation did not make every group accept it as a discovery. The candidate Kepler-1708b-i later drew debate as well. Neither name is confirmed. Still, they show how a moon’s signal can sit in the data used to find a planet, then disappear when the model looks for only one body.