To us, Earth seems vast and limitless, with mountains and valleys, deserts and seas, and many places that remain largely unexplored. However, our planet is only a tiny part of the universe, which has countless stars and planets we don’t even know exist. Astronomers using the James Webb Space Telescope recently uncovered a planet in the Kepler-51 system, located 2,615 light years from Earth. The new planet called Kepler-51e is the fourth planet in a unique system, which stands out with its three previous planets all being ultralight “super puffs.”
As their name suggests, super puff planets have extremely low densities. Those in the Kepler system are about Saturn’s volume, yet just a few times Earth’s mass. As a result, they have cotton-candy-like densities. The Kepler-51 planets supposedly have minute cores, with enormous atmospheres containing hydrogen and helium. Astronomers speculate about how they formed and continue to withstand their star’s radiation.
The discovery of another planet may create even more questions, but also might provide answers about this enigmatic system. According to Jessica Libby-Roberts of Penn State’s Center for Exoplanets and Habitable Worlds, “Super puff planets are fairly rare, and when they do occur, they tend to be the only one in a planetary system.” The Kepler-51 system defies this trend by having three, as well as another planet that might be a super puff as well. The researchers are still studying data to understand how super puff planets form.
Researchers from Penn State and Osaka Universities discovered Kepler-51e while trying to analyze another planet in the system, Kepler-51d. Kepler-51d seemed to transit (or pass in front of) its parent star two hours prior to the expected time. When starlight filters through a planet’s atmosphere as it makes a transit, different elements absorb the light at different wavelengths. This helps astronomers study these “fingerprints” to decipher the atmosphere’s composition. Additionally, the duration and magnitude of the star’s reduced brightness can indicate a planet’s size.
The astronomers had successfully predicted Kepler-51d’s transit in 2023 using their model composed of just three planets. They expected the planet to transit again at 2 a.m. EDT in June 2023, but it was two hours early. Their calculations had been uncertain by only fifteen minutes, so the discrepancy made it clear that something was off.
Archived data revealed that another planet was the only viable explanation, marking the first time the James Webb Space Telescope and transit timing variations unveiled an undiscovered world. The four-planet model that the scientists found explains data collected throughout the last fourteen years.
Kepler-51e likely has a mass about the same as the others in the system, with an approximately 264-day circular orbit. The new model of the Kepler system involves the three previously known planets having slightly different masses than originally believed, but they are still categorized as super puffs. Kepler-51e has a slight impact on other planets in the system, which is why Kepler-51d made an early transit. As the researchers have yet to observe a transit of Kepler-51e itself, they are unable to find its radius or density. Consequently, whether or not it is a super puff is unknown.
Kepler-51e is just within its parent star’s habitable zone. As it was only just discovered, it is unknown whether or not it can actually support life. Nonetheless, there may still be even more planets in the Kepler-51 system and beyond that are yet to be discovered, and the possibility of life beyond our boundless yet tiny Earth remains a mystery.
