Astronomers Uncover BEBOP-1c: Exoplanet in a Twin-Star, Multiplanetary System Mirrors Star Wars’ Tatooine

A global consortium of astronomers has made public the detection of an additional planet within the seldom-seen multiplanetary circumbinary system, referred to as either BEBOP-1 or TOI-1338. Designated as BEBOP-1c, this newly discovered planet was pinpointed using the Doppler technique, which involves determining the mass of the planet by gauging the velocity of stars. The planet orbits in a period of 215 days and boasts a mass that is 65 times greater than that of Earth.

The University of Birmingham’s astronomers have discovered BEBOP-1c, marking the second recorded instance of a multiplanetary circumbinary system. Circumbinary systems host planets that orbit two central stars simultaneously, rather than just one, as in our Solar System. The University of Birmingham led the research, which has been published in the current issue of the journal Nature Astronomy.

BEBOP-1c was named after the project that collected the data, BEBOP, which stands for Binaries Escorted By Orbiting Planets. BEBOP-1 is alternatively known as TOI-1338. Earlier in 2020, a circumbinary planet, TOI-1338b, was identified within the same system using data from NASA’s TESS space telescope, a project that the Birmingham team also contributed to.

A commemorative illustration marks the detection of BEBOP-1c using the radial-velocity method, demonstrating the shift in astronomy from manual telescope observations to digital data analysis and interpretation. BEBOP-1c was identified using the ESPRESSO instrument at the Very Large Telescope in Chile, and by HARPS, at the 3.6m telescope, both managed by the European Southern Observatory (ESO). Credit goes to Amanda Smith from the University of Birmingham.

Dr. Matthew Standing, lead author and a researcher at The Open University, explains that while the transit method allowed them to measure TOI-1338b’s size, they could not measure its most critical characteristic – its mass. At the time, the BEBOP team was monitoring the system using another detection technique known as the Doppler method, which led to the first exoplanet detection, a feat that earned Mayor and Queloz the Nobel Prize in 2019, says Amaury Triaud, a professor at the University of Birmingham.

Despite several years of hard work and advanced instruments installed on two telescopes located in the Atacama Desert in Chile, the team was not able to measure TOI-1338b’s mass. However, they discovered a second planet, BEBOP-1c, and determined its mass.

“Circumbinary systems are still quite rare, with only 12 known to date, and this one is only the second found to host more than one planet,” says David Martin, an astronomer and Sagan Fellow at the Ohio State University.

“BEBOP-1c orbits every 215 days and is 65 times larger than Earth, approximately five times less massive than Jupiter,” continues Dr. Standing. The COVID pandemic affected the process of confirming this complex system, as the Chilean telescopes were closed for six months during a crucial phase of the planet’s orbit.

While only two planets have been identified in the TOI-1338/BEBOP-1 circumbinary system so far, it’s possible more could be discovered in the future.

Circumbinary planets are crucial to advancing our understanding of planetary formation. “Planets form in a disc of material surrounding a young star, where mass progressively congregates into planets,” explains Dr. Lalitha Sairam, a researcher at the University of Birmingham. In circumbinary systems, this disc encompasses both stars, making it easier to pinpoint the location and conditions of planet formation.

The size of BEBOP-1c is yet to be determined, but the researchers intend to use the transit method to measure it. While the team did not detect the inner planet, TOI-1338b, they were able to ascertain its low density, which is less than that of a Victoria Sponge cake, making it a unique candidate for further study with the James Webb space telescope.

Reference: “Radial-velocity discovery of a second planet in the TOI-1338/BEBOP-1 circumbinary system” by Matthew R. Standing et al., 12 June 2023, Nature Astronomy.
DOI: 10.1038/s41550-023-01948-4

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More about BEBOP-1c discovery

• NASA’s TESS Space Telescope
• Very Large Telescope
• European Southern Observatory
• James Webb Space Telescope
• Nature Astronomy Journal
• University of Birmingham