An international team of astronomers has announced the second-ever discovery of a circular, multi-planetary system.
Circular systems have planets orbiting two stars at the center instead of just one, as is the case in our solar system. Circular planets orbit both stars simultaneously. The discovery, which was led by researchers at the University of Birmingham, is reported in the journal natural astronomy.
The newly discovered planet is called BEBOP-1c, after the project that collected the data. BEBOP stands for Binaries with Orbiting Planets. The BEBOP-1 system is also known as TOI-1338.
In 2020, a round planet called TOI-1338b was discovered in the same system using data from NASA’s TESS Space Telescope, to which the Birmingham team also contributed. This planet was discovered by the transit method and was observed because it passed in front of the two brighter stars on several occasions.
“The transit method allowed us to measure the size of TOI-1338b, but not its mass, which is the primary metric for a planet,” said lead author Dr. Matthew Standing, who completed his PhD. at the University of Birmingham and is now a researcher at the Open University.
The BEBOP team was already monitoring this system using another detection method at the time, called the Doppler method. This method, also called the “wobble” method, or the radial velocity method, relies on accurately measuring the velocity of stars.
“This is the same method that led to the first detection of exoplanets, and Mayor and Kelos received the Nobel Prize in 2019,” said Amory Triaud, Matthew’s supervisor, a professor at the University of Birmingham.
Using state-of-the-art instruments mounted on two telescopes located in Chile’s Atacama Desert, the team attempted to measure the mass of the planet observed by TESS. Despite their best efforts and years of work, the team couldn’t make it, but instead discovered the second planet, BEBOP-1c, and measured its mass.
“Only 12 ring systems are known to date, and this is only the second to host more than one planet,” said David Martin, an astronomer and Sagan Fellow at Ohio State University.
“BEBOP-1c has an orbital period of 215 days, a mass 65 times greater than Earth’s and about five times less than that of Jupiter,” Dr. Standing continues. “This was a difficult system to confirm, and our observations were interrupted by the COVID pandemic when telescopes in Chile were closed for six months during an important part of the planet’s orbit. That part of the orbit only became visible again last year, when we finished the detection.”
Currently, only two planets are known in the TOI-1338/BEBOP-1 rotation system but more may be identified in the future, with similar observations as made by the team.
Although circular planets are rare, they are important in advancing understanding of what happens when a planet forms.
“Planets are born in a disk of material surrounding a young star, where mass gradually coalesces into planets,” explains Dr Lalitha Sairam, a researcher at the University of Birmingham and second author of the study.
“In the case of circular geometry, the disk surrounds both stars. Since both stars orbit each other, they act like a giant paddle that disturbs the disk close to them and prevents planet formation except for the quiet and distant regions of the Earth. The binary. It is easier to determine the location and conditions of planet formation in the systems circular compared to single stars such as the sun.
The team doesn’t yet know the size of BEBOP-1c, only its mass, however the researchers will try using the transit method now to measure the size of BEBOP-1c.
Although the inner planet TOI-1338b was not detected, the team was able to place strict upper limits on its mass. The planet’s density is now known to be less than that of a Victoria sponge cake, a rarity that makes this planet ideal for further studies with the James Webb Space Telescope. If these observations occur, they could reveal the chemical environment in which this rare round planet formed.
Discovery of the radial velocity of a second planet in the TOI-1338/BEBOP-1 ring system, natural astronomy (2023). DOI: 10.1038/s41550-023-01948-4.
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