A planet resembling a smaller version of Neptune orbits one of two Sun-like stars that also orbit each other. This planet, located in the “habitable zone,” poses new questions to existing theories of planetary formation due to its moderate temperature and unique characteristics.
Key Facts
Astronomers once believed that our solar system—with its small, rocky planets close to the Sun and gas giants farther out—was typical. However, recent discoveries suggest otherwise. The TOI 4633 system, featuring a “mini-Neptune” with an Earth-like, 272-day orbit around one of two stars, challenges these ideas. The unusual orbits of this mini-Neptune and a possible sibling planet raise questions about the stability and formation of such planetary systems.
Unique Characteristics of TOI 4633
Among the thousands of exoplanets confirmed in our galaxy, most are detected using the “transit” method, which measures the dip in starlight as a planet crosses its star. Most transit detections involve planets with short orbits, lasting only a few days or weeks. However, TOI 4633 c’s 272-day orbit makes it part of a select group of 175 planets with orbits longer than 100 days, and one of only 40 with orbits over 250 days.
Detected by TESS (Transiting Exoplanet Survey Satellite), TOI 4633 c orbits within the habitable zone, where liquid water could potentially form on a planetary surface. Despite its placement, the planet likely has a dense atmosphere similar to Neptune’s, ruling out surface water. However, it might host a habitable moon, a concept reminiscent of the fictional Pandora. The system’s brightness makes it a prime target for the search for such “exomoons.”
Additional Mysteries
The system has more intriguing features. Another detection method revealed a potential sibling planet with a 34-day orbit, identified through “radial velocity” measurements. This method tracks the slight shifts in starlight caused by a planet’s gravitational pull on its star. Further investigations are required to confirm the presence of this sibling planet.
This system is also significant for understanding binary star systems, where two stars orbit each other. In this case, a companion star orbits the primary star every 230 years, allowing them to come relatively close. The combination of an oval-shaped mutual orbit, close stellar approach, and a transiting planet on a long orbit provides a unique opportunity to test theories on the formation and stability of planetary systems.
Fun Facts
Planet TOI 4633 c was discovered by 15 citizen scientists through the Planet Hunters TESS citizen science project. These volunteers examined TESS data, identifying “light curves” that indicate planetary transits. Additionally, archival data from the Washington Double Star Catalog, maintained by the U.S. Naval Observatory and collected between 1905 and 2011, assisted in this discovery.
