Astronomers have uncovered a remarkable fourth planet, Kepler-51e, orbiting within the habitable zone of the star Kepler-51.
This discovery, made possible by the James Webb Space Telescope (JWST) and the Apache Point Observatory (APO), sheds new light on one of the most perplexing planetary systems ever studied.
The Kepler-51 system has long intrigued scientists due to its three previously discovered “super puff” planets—Kepler-51a, Kepler-51b, and Kepler-51c. These planets, with densities as low as cotton candy, defy conventional models of planet formation. Now, Kepler-51e has joined the mix, marking the first planet identified within the star’s habitable zone.
“Kepler-51e has an orbit slightly larger than Venus and is positioned just inside the habitable zone,” revealed Jessica Libby-Roberts, a postdoctoral researcher at Penn State’s Center for Exoplanets and Habitable Worlds and co-first author of the discovery paper.
Although 2,556 light-years separate Earth from Kepler-51e, the team’s work highlights how gravitational influences between planets can reveal the existence of worlds that don’t transit their stars. This approach could transform how scientists hunt for planets where life might thrive.
A Chance Discovery Sparks Curiosity
Kepler-51e’s discovery was unexpected. Researchers were initially focused on observing Kepler-51a using JWST and APO, but their simulations didn’t align with real-time observations. Instead of appearing at the predicted time, the star’s brightness dipped earlier than anticipated, signaling something extraordinary.
“At first, we were puzzled by the early appearance of Kepler-51d,” said Kento Masuda, an associate professor at Osaka University and co-first author. “After rechecking our models, we realized that a fourth planet provided the best explanation for the observed gravitational anomalies.”
Through extensive simulations, the team found that Kepler-51e likely shares a mass similar to its cotton candy-like siblings and completes a circular orbit around its star in about 264 days.
“This marks the first time a planet has been discovered through transit timing variations using JWST,” Masuda noted.
The Mysteries of Cotton Candy Planets Deepen
While the discovery of Kepler-51e excites the possibility of finding habitable planets, it also raises more questions. The previously known planets in the system are exceptionally large, low-density bodies with hydrogen-helium atmospheres that have somehow survived the harsh radiation of their young star.
“The three super puffs are about the size of Saturn but weigh only a few times more than Earth,” Libby-Roberts explained. “Their formation and the stability of their atmospheres remain mysteries, and now we have to add Kepler-51e to the equation.”
The team suspects Kepler-51e could offer new insights into these enigmatic worlds. Could it share their low density, or does it defy the pattern?
Looking Beyond Kepler-51e
The discovery of Kepler-51e opens new doors for exploring the system. Researchers aim to refine measurements of its size and orbit through further observations of its gravitational effects on the visible planets. They also plan to extend their search beyond the system’s known boundaries, suspecting that additional hidden planets might await discovery.
“A lot more could be happening farther from the star if we take the time to investigate,” Libby-Roberts said.
The Kepler-51 system remains a cosmic enigma, with its “cotton candy” planets challenging established planetary science theories. As astronomers continue their search, these discoveries could help refine techniques for finding habitable planets and, perhaps, life beyond Earth.
