Scientists accidentally discover a Tatooine-like exoplanet that orbits two stars

BEBOP-1c is the newly discovered planet, while the first one in this system is TOI-1338b.
Mrigakshi Dixit
In this illustration, TOI 1338 b is silhouetted by its host stars.
In this illustration, TOI 1338 b is silhouetted by its host stars.

NASA's Goddard Space Flight Center/Chris Smith 

The term 'Tatooine' is pretty popular in science fiction series such as Star Wars. It refers to a planet that is circling two stars at the same time.  

Now, in a huge breakthrough, scientists have discovered a new exoplanet in an already known Tatooine system or circumbinary system. 

BEBOP-1c is the newly discovered exoplanet, while the first one in this system is TOI-1338b. According to scientists at the University of Birmingham, this is just the second known “Tatooine-like multi-planetary system.”

“Only 12 circumbinary systems are known so far, and this is only the second that hosts more than one planet,” said David Martin, an astronomer and Sagan Fellow at the Ohio State University, in an official release. 

The two planets orbit the pair of stars at once. The newly discovered exoplanet is named after the BEBOP (Binaries Escorted By Orbiting Planets) program.

The accidental discovery 

The team discovered this new exoplanet by chance while studying the circumbinary system's first known planet (TOI-1338b). 

TOI-1338b was spotted in 2020 using NASA's TESS space telescope.

“The transit method permitted us to measure the size of TOI-1338b, but not its mass which is the planet’s most fundamental parameter,” said Dr. Matthew Standing, who is the lead author of this study. Dr. Standing earned his Ph.D. at the University of Birmingham and is currently a researcher at The Open University.

The BEBOP team continued to investigate this system by employing a technique known as the Doppler method, which measures the velocity of stars.

The researchers utilized two telescopes in Chile's Atacama Desert to determine the mass of TOI-1338b. Despite years of effort, the BEBOP team was unable to precisely determine the mass of TOI-1338b. 

However, their efforts were rewarded in a different way when they discovered a second planet in the same system. And, fortunately, they were able to determine the mass of BEBOP-1c. “BEBOP-1c has an orbital period of 215 days, and a mass 65 times larger than Earth, which is about five times less than Jupiter’s mass,” said Dr Standing.

Only two exoplanets are known to exist in this circumbinary system at present, but scientists predict that there may be others waiting to be discovered. 

The team aims to use the James Webb space telescope to collect data on the atmospheric chemistry of this peculiar system. 

The study has been published in the journal Nature Astronomy

Study abstract:

Circumbinary planets, those that orbit around both stars of a central binary star system, challenge our understanding of planet formation. With only 12 binary systems known to host circumbinary planets, identifying more of these planets, along with their physical properties, could help to discern some of the physical processes that govern planet formation. Here we analyse radial-velocity data obtained by the HARPS and ESPRESSO spectrographs and report the detection of BEBOP-1 c, a gas giant planet with a mass of 65.2 ± 11.8 Earth masses (M⊕) orbiting around both stars of an eclipsing binary star system with a period of 215.5 ± 3.3 days. The system TOI-1338, hereafter referred to as BEBOP-1, which also hosts the smaller and inner transiting planet TOI-1338 b, is only the second confirmed multiplanetary circumbinary system. We do not detect TOI-1338 b with radial-velocity data alone, and we can place an upper limit on its mass of 21.8 M⊕ with 99% confidence. TOI-1338 b is amenable to atmospheric characterization using JWST, so the BEBOP-1 system has the potential to act as a benchmark for circumbinary exo-atmospheric studies.

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