Astronomers Unveil Second Multiplanetary Circumbinary System: BEBOP-1c Joins TOI-1338

An international team of astronomers, led by researchers at the University of Birmingham, has made an extraordinary breakthrough in the field of astronomy. Their latest discovery involves the identification of a second-ever multiplanetary circumbinary system, shedding light on the unique dynamics of planet formation in systems where two stars take center stage. This remarkable finding, named BEBOP-1c, has been published in the esteemed journal Nature Astronomy.

The TOI-1338 system, where BEBOP-1c resides, first gained attention in 2020 with the discovery of its first planet, TOI-1338b, using data from NASA's TESS space telescope. The transit method, which detects a planet as it passes in front of one of the binary stars, was used to identify TOI-1338b, providing valuable information about its size. However, determining the planet's mass, a crucial parameter for understanding its nature, remained a challenge.

Undeterred, the industrious BEBOP team employed a different method called the Doppler or radial-velocity method. This groundbreaking approach, which won the 2019 Nobel Prize in Physics, involves precise measurements of stellar velocities. With state-of-the-art instruments installed on telescopes in Chile's Atacama Desert, the team embarked on a mission to determine the mass of TOI-1338b. While their efforts to measure TOI-1338b's mass were unsuccessful, they stumbled upon an unexpected treasure—a second planet, BEBOP-1c, whose mass they successfully measured.

BEBOP-1c orbits the TOI-1338 system with a period of 215 days and has a mass approximately 65 times that of Earth, but significantly smaller than Jupiter. This intriguing addition adds a new dimension to the enigmatic TOI-1338 system. Detecting BEBOP-1c was no easy task, as the COVID-19 pandemic interrupted observations for six critical months during a crucial phase of its orbit. However, when observations resumed, the team finalized their remarkable discovery.

The TOI-1338/BEBOP-1 circumbinary system now boasts two known planets, with the potential for further discoveries through future observations. These rare circumbinary planets play a vital role in expanding our understanding of planetary formation mechanisms.

Dr. Lalitha Sairam, a researcher at the University of Birmingham and the study's second author, explains the intricate interplay between planets and their binary star hosts. In circumbinary systems, planets typically form within a disk of matter encircling a nascent star. However, in these systems, the disk encompasses both stars, creating an environment where the binary motion disrupts and inhibits planet formation, except in remote regions far from the stars. This unique configuration makes circumbinary systems ideal for pinpointing precise locations and conditions conducive to planet formation, contrasting with the complexity surrounding single-star systems like our Sun.

Future efforts will focus on using the transit method to determine the size of BEBOP-1c, which currently remains unknown despite its measured mass. Although the inner planet, TOI-1338b, was not detected in this study, the team successfully established stringent upper limits on its mass. Notably, TOI-1338b possesses a density lower than that of a Victoria sponge cake, making it an enticing prospect for further investigations using the upcoming James Webb Space Telescope. These anticipated observations hold the promise of unraveling the chemical intricacies of this rare circumbinary planet's formative environment.

In conclusion, the groundbreaking discovery of the second-ever multiplanetary circumbinary system, BEBOP-1c, by the University

of Birmingham-led team of astronomers opens up new avenues of exploration in our understanding of planet formation. The TOI-1338/BEBOP-1 system's unique dynamics and the presence of two known planets provide valuable insights into the intricacies of planetary systems in binary star configurations. With future observations and the advent of advanced telescopes, scientists eagerly anticipate unraveling the mysteries surrounding these rare celestial companions and the secrets they hold about the formation of planets.