Exoplanet found in the habitable zone of a binary star system

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In a major advancement in space science, astronomers and citizen scientists have discovered an exoplanet within the habitable zone of a binary star system. This system features not only two stars but potentially another exoplanet as well.

As it passed in front of one of its stars, the planet, similar in size and composition to Neptune, momentarily blocked the star's light in an event resembling a solar eclipse on Earth.

Scientists typically use this discovery method, known as the "transit method," to find planets that orbit close to their host stars.

Transiting planets on long orbital periods

The new planet, officially named TOI 4633 c but also known as Percival, breaks the mold with its lengthy 272-day orbit. This makes it a rare find due to its relatively distant position from its star.

"Transiting planets on long orbital periods, in particular, allow for new investigations into the formation, migration, and long-term stability of planetary systems," wrote the study authors. "The comparison between planets with short and long orbital periods, for example, allows us to probe how equilibrium temperatures affect planet formation."

Citizen scientists and exoplanet discoveries

Citizen scientists participating in the Planet Hunters TESS program first brought this discovery to light as they sifted through data from NASA's Transiting Exoplanet Survey Satellite (TESS).

These volunteers, from all corners of the globe, play a crucial role in identifying celestial bodies that might otherwise be missed by automated systems.

Simon Bentzen, a Danish citizen scientist and an active participant since 2018, shared his excitement about the discovery. "Every time I spot a possible transit, I can feel my heart beat faster and my excitement rise extensively. I'm very happy that I helped find the new system. I hope that the new planets can help contribute to our understanding of planet formation and help answer other interesting planetary questions," said Bentzen.

Exoplanet in a binary star system

Further investigations show the planet orbits the brighter star of a tight binary system, so close that the stars appear as one from Earth. Historical data over 119 years confirmed their binary nature.

The lead researcher and principal investigator of the Planet Hunters TESS project, Nora Eisner, elaborated on the significance of this system.

"Finding planets in multi-star systems is crucial for our understanding of how you can make different planets out of the same material," said Eisner. "It's quite exciting that we found this one because planets are estimated to be half as likely to form in a binary star system compared to single-star systems."

Prospects for moon discovery and life potential

The excitement surrounding this discovery does not stop at the planet itself. Since TOI 4633 c is in the habitable zone and orbits a particularly bright star, it becomes a prime candidate for future exomoon detection campaigns.

While TOI 4633 c lacks a solid surface and is likely enveloped in a thick atmosphere of water vapor, hydrogen, and methane, any potential moons could offer solid surfaces possibly capable of supporting water and, by extension, life.

"If this planet were to have a moon, that moon would likely have a solid surface, which could then be a great place to find water," said Eisner. She further noted that the unique orbital dynamics and brightness of the system enhance the feasibility of detecting moons around this exoplanet.

Exploring multi-star systems

Nearly half of all sunlike stars in our galaxy are part of multi-star systems, and the research presents a broader implication for the study of these systems.

"If we were able to constrain where the planets orbit, it would really offer a stepping stone to open up our understanding of exoplanet formation," noted Eisner. Such insights could eventually allow scientists to make educated guesses about potential planetary bodies around other stars based on their observable properties.

Exoplanet discovery: Inspiring collaboration

The discovery of the exoplanet TOI 4633 c not only expands our knowledge of planetary systems but also underscores the invaluable contributions of citizen scientists in pushing the boundaries of space exploration.

It's a testament to the synergy between professional scientists and enthusiastic amateurs, and a vivid reminder of the mysteries that still await us in the cosmic expanse.

The study is published in The Astrophysical Journal.

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