'Mini-Neptune' discovered that has two stars in an orbit that puzzles astronomers

A fascinating discovery has emerged in the realm of planetary systems: a planet resembling a smaller version of Neptune (mini-Neptune) orbits one of two Sun-like stars in a binary system.

This intriguing planet resides in the “habitable zone,” where temperatures might be moderate, challenging current theories about planet formation.

Understanding binary star systems

A binary system consists of two stars orbiting a common center of mass. These systems are common in the universe, with many stars, including some visible to the naked eye, being part of binary systems.

The stars can vary in size, brightness, and distance from each other. Their interactions affect their evolution and can lead to phenomena such as stellar eclipses or even the merging of the stars.

Binary systems are crucial for understanding stellar dynamics and evolution, as they provide insights into the mass, structure, and life cycle of stars through their mutual gravitational influences.

Mini-Neptune in binary system TOI 4633

Astronomers once believed that our solar system, with its calm, middle-aged Sun hosting rocky planets nearby and gas giants further out, was the norm.

However, advanced planet-hunting technology has revealed that other planetary systems can be vastly different. The binary system known as TOI 4633 is particularly unusual. It features a “mini-Neptune” that follows an Earth-like orbit around one of two stars orbiting each other.

The unique arrangement of the stars and planets in this system raises questions about the stability and formation of planetary systems.

Among the thousands of confirmed exoplanets in our galaxy, most were discovered using the “transit” method, which detects the tiny dip in starlight as a planet passes in front of its star.

Typically, these detections involve planets with short orbits lasting only a few days or weeks. The discovery of planet TOI 4633 c, with its 272-day orbit, is a significant departure from this trend.

Detected using the Transiting Exoplanet Survey Satellite (TESS), TOI 4633 c, also known as Percival, is one of the few transiting planets with an orbit longer than 100 days. Only 40 of the discovered planets have orbits exceeding 250 days.

The mini-Neptune, situated in the habitable zone, might not have liquid water due to its dense atmosphere, similar to Neptune’s. However, the possibility of a habitable moon exists, making it a prime target for future exomoon searches.

“Weird” system should be unstable

Adding to the mystery, measurements using a second detection method, “radial velocity,” suggest a possible sibling planet with a 34-day orbit.

This planet does not transit its star from Earth’s perspective, so its presence was inferred from the gravitational pull it exerts on the star. Further investigations are required to confirm this sibling planet.

The binary system also offers valuable insights into binary star systems and planetary systems, where two stars orbit each other.

In this case, the companion star orbits the primary star in just 230 years. The stars’ close approach and oval-shaped orbit, combined with a transiting planet on a long orbit, make TOI 4633 a unique system.

Consequently, it allows scientists to test theories about planetary formation and the stability of unusual orbital configurations over billions of years.

Citizen scientists and historical data

Planet TOI 4633 c’s discovery is credited to 15 “citizen scientists” who analyzed TESS data through the Planet Hunters TESS project.

Approximately 40,000 volunteers regularly inspect light curves, looking for dips in starlight that indicate a planet crossing.

The investigation also benefited from archival data from the Washington Double Star Catalog, maintained by the U.S. Naval Observatory, dating back to between 1905 and 2011.

Still much to learn from “mini-Neptunes”

In summary, this discovery broadens our understanding of planetary systems while also highlighting the fact that science still has a lot to learn about the universe.

The collaboration between professional astronomers and dedicated citizen scientists demonstrates the power of collective effort in pushing the boundaries of scientific knowledge.

This remarkable find of the mini-Neptune TOI 4633 c underscores the importance of continued exploration and study, promising exciting new insights into the formation and stability of planetary systems in the universe.

The full study was published in the journal The Astronomical Journal.

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