Scientists using the **James Webb Space Telescope (JWST)** and the **Apache Point Observatory (APO)** have made an exciting discovery—a new planet, **Kepler-51e**, orbiting within the habitable zone of the distant star **Kepler-51**. This marks the first time researchers have found a planet in this system with conditions that could potentially support life.


Previously, astronomers had identified three unusual, low-density planets in the Kepler-51 system—**Kepler-51a**, **Kepler-51b**, and **Kepler-51c**. These planets, often referred to as "super puff" or "cotton candy" planets due to their large size and extremely low density, puzzled researchers. Now, the discovery of Kepler-51e adds a new layer of intrigue to this already mysterious system.


### A Chance Discovery


The finding was a happy accident. The research team originally aimed to study Kepler-51a more closely using the JWST and APO. However, their observations didn’t go as planned.  


“By 2 a.m., then 3 a.m., we hadn’t seen any changes in the star’s brightness,” explained **Jessica Libby-Roberts**, a postdoctoral fellow at Penn State’s Center for Exoplanets and Habitable Worlds and co-lead author of the study.  


When the team reviewed their data, they noticed an unexpected dip in the star’s brightness—two hours earlier than anticipated. This discrepancy led them to re-examine their models, ultimately revealing the presence of a previously unknown planet.


### Gravitational Clues and a Four-Planet Model


The researchers were initially baffled by why Kepler-51d, one of the known planets, appeared earlier than expected during its transit. No adjustments to the three-planet model could account for the timing mismatch.  


**Kento Masuda**, an associate professor at Osaka University and co-lead author, explained that the team conducted a "brute force" search, running numerous simulations to find an explanation. They eventually identified a four-planet model that fit the data best. This model suggested that **Kepler-51e** is a low-mass planet with a circular orbit of about 264 days—placing it just inside the star’s habitable zone.


“This is the first time JWST has discovered a planet using transit timing variations,” Masuda noted.


### What Makes Kepler-51e Special?


Kepler-51e’s orbit is slightly larger than Venus’s orbit around the Sun, but its location within the habitable zone is especially noteworthy. Although it is difficult to study the planet directly due to its distance from Earth—about **2,556 light-years away**—its detection highlights a promising method for finding potentially habitable exoplanets by studying their gravitational influence on other planets.


### Challenges of the Kepler-51 System


The discovery of Kepler-51e deepens the mystery of the system. The three previously known "super puff" planets are massive, about the size of Saturn, but with densities similar to cotton candy. Their low density is likely due to small cores surrounded by thick atmospheres of hydrogen and helium. However, it remains unclear how these planets formed and why their atmospheres haven’t been stripped away by their young star’s intense radiation.


Adding Kepler-51e to the mix raises even more questions. Is it another super puff, or does it have different characteristics? And are there even more undiscovered planets in the system?  


“If explaining three super puffs in one system wasn’t hard enough, now we have to figure out how a fourth planet fits in,” Libby-Roberts said.


### What’s Next?


The research team plans to refine their measurements of Kepler-51e’s size and orbit using further observations. Since this planet does not transit its star, researchers will rely on its gravitational effects on the other planets to learn more. They also hope to search for additional planets farther from the star.  


“A lot more could be happening in the outer parts of this system if we take the time to look,” Libby-Roberts said.


By unraveling the dynamics of the Kepler-51 system, scientists hope to better understand the formation of "cotton candy" planets and refine techniques for identifying planets in habitable zones—key steps in the search for extraterrestrial life.