Kepler Space Telescope’s Mission
Launched by NASA back in 2009, the Kepler telescope was on a mission to look for Earth-sized planets in orbit of other stars. It was shut down in 2018 having discovered 2,662 exoplanets and observed 530,506 stars. It repeatedly recorded the brightness of thousands of stars and the data was checked to look for dips that could be explained by a planet partially blocking the light. If consistent dips indicated a likely planet, it was considered a planet candidate. Without being added to the catalog of known exoplanets, over 5,000 such candidates were identified in Kepler and TESS data.
Three “Planets” Were Actually Stars
Follow-up research of the collected data was conducted to rule out alternative explanations before the candidates could be listed as exoplanets. This was initially done by looking for movement under the presumed planet’s gravitational influence. However, this method required a lot of time and equipment to do, so scientists moved to statistical verification techniques. During the reevaluation of the data, it was found that Kepler-854b, Kepler-840b, and Kepler-699b were more likely small stars rather than planets.
How the Error Was Discovered
According to the research authors, the aforementioned objects were simply too large to be planets. Prajwal Niraula, an MIT graduate student, stated that most exoplanets are Jupiter-sized or smaller, and what they found exceeded twice the size of Jupiter, which meant they couldn’t be planets. One of the study authors, Dr. Avi Shporer, states that making sure that the list of planets is not contaminated by incorrect data, as people will rely on it for future research when studying the population of planets as a whole.