ircumbinary planets, also known as binary star planets or Tatooine planets (named after the fictional planet in the “Star Wars” franchise), are a type of exoplanets that orbit around two stars in a binary star system. Unlike most planets in our solar system that orbit around a single star, circumbinary planets have a more complex orbital configuration.
In a binary star system, two stars orbit around a common center of mass. A circumbinary planet, in turn, orbits this center of mass, maintaining a stable gravitational relationship with both stars. This arrangement can be challenging for planets due to the gravitational forces exerted by the two stars, which can lead to unstable orbits.
Binary star systems, where two stars orbit each other, are prevalent throughout the Milky Way galaxy, with approximately half of the stars similar to our Sun existing in such configurations. However, until recently, only a single binary system had been identified as harboring multiple planets.
“Circumbinary planets were originally thought not to exist, since the binary stars stir up the planet-forming disks, creating a harsh environment for planets to form. This all changed with the discovery of Kepler-16b in 2011 by the Kepler space telescope.”
~ Matthew Standing, Study Lead Author
Utilizing the advanced capabilities of the European Southern Observatory and the Very Large Telescope, both located in Chile’s Atacama Desert, astronomers aimed to determine the mass of TOI-1338b. Despite their concerted efforts, they were unable to achieve that specific goal. Instead, an unexpected outcome emerged — a second planet was uncovered during their observations.
Named in honor of the data collection project, BEBOP (Binaries Escorted By Orbiting Planets), the newly discovered celestial body has been designated as BEBOP-1c. BEBOP-1c is a gas giant with a mass of approx. 65 times that of Earth, but around five times less massive than Jupiter. It gracefully revolves around its stellar counterparts, maintaining a distance of roughly 79% of an astronomical unit (AU) — a unit equivalent to the average distance between Earth and the sun.
Completing its orbit in approximately 215 days, BEBOP-1c embarks on a captivating journey around its dual suns. In comparison, TOI-1338b, located at a distance of about 46% of an AU from its stars, completes its orbit in around 95 days. Scientists estimate that TOI-1338b possesses a mass no more than 22 times that of Earth, adding further intrigue to its celestial nature.
According to researchers, previous discoveries of circumbinary planets relied on expensive space telescopes like Kepler and TESS, costing hundreds of millions of dollars. However, this recent breakthrough holds significant importance as it demonstrates that detecting such planets doesn’t necessarily require costly space telescopes.
Instead, ground-based telescopes can be utilized along with the radial-velocity technique, provided there is meticulous planning and careful target selection. However, detecting circumbinary planets using the radial-velocity technique poses challenges due to the combined light emitted by both stars. This makes it intricate to gather precise data on the motions of the stars, essential for confirming the existence of these captivating circumbinary worlds.
To date, the TOI-1338/BEBOP-1 circumbinary system has revealed the existence of just two known worlds. Nonetheless, the scientists highlighted the potential for further identifications in the future. Ongoing research endeavors hold the promise of confirming the size of BEBOP-1c and determining the mass of TOI-1338b.
Equally crucial is the next phase, which involves measuring the atmospheric chemistry of circumbinary planets and drawing comparisons with planets orbiting single stars. This avenue of investigation opens doors to gaining a deeper understanding of these unique celestial bodies and their distinctive characteristics. Webb telescope is very well suited for these kinds of observations.