Scientists have discovered a new planet TOI-1338 c (also known as BEBOP-1 c) — the second-ever known planetary system orbiting twin stars. Only two worlds are known in the TOI-1338/BEBOP-1 circumbinary system so far.
Astronomers have pondered the existence of twin-sun planets like Tatooine, the fabled home planet of Luke Skywalker, for many years. Now, researchers have found a brand-new system that resembles Tatooine and has several worlds.
About half of the sun-like stars in the Milky Way galaxy are in binary systems, which are made up of two stars orbiting one another. Astronomers have so far confirmed the discovery of 14 circumbinary planets, or planets that revolve simultaneously around two stars in a binary system.
“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,” study lead author Matthew Standing, an astrophysicist at the Open University in England, told Space.com. “This all changed with the discovery of Kepler-16b in 2011 by the Kepler space telescope. This discovery showed that it must be possible for these planets to form.”
Up to this point, only Kepler-47, a binary system in the constellation Cygnus, the Swan, nearly 5,000 light-years away, was known to contain many planets. With Kepler-47 b, d, and c, this circumbinary multi-planetary system contains an astounding three known worlds.
The newly discovered planet is known as BEBOP-1c after the BEBOP project
The TOI-1338 binary system, which is around 1,320 light-years away from Earth in the constellation Pictor, was the subject of the recent study. The circumbinary planet TOI-1338b was discovered in 2020 by NASA‘s TESS satellite telescope, which is looking for exoplanets.
The researchers attempted to determine the mass of TOI-1338b using the European Southern Observatory and the Very Large Telescope, both of which are situated in Chile’s Atacama Desert. They tried their hardest, yet they were unable to succeed. Instead, they found another planet.
“With only 15 of these circumbinary planets known out of the over 5,200 total exoplanets discovered so far, it is exhilarating to be a part of this emerging branch of exoplanet science,” Standing said. “Our preliminary results show that circumbinary planets seem to exist as frequently as planets around single stars like our sun.”
The newly discovered planet is known as BEBOP-1c after the BEBOP project, which stands for Binaries Escorted By Orbiting Planets, and was responsible for gathering the data. (BEBOP-1 refers to the binary system TOI-1338 by another name.)
BEBOP-1c is a gas giant with a mass that is roughly 65 times that of Earth and five times that of Jupiter. It travels around its suns in about 215 days and orbits its stars at a distance of around 79% of an astronomical unit (AU; one AU is the average distance between the Earth and the sun).
In contrast, TOI-1338b takes 95 days to orbit its stars and is only 46% of an AU away from them. Its maximum mass, according to scientists, is 22 times that of the Earth.
A high school student assisted in the discovery of TOI-1338b as it repeatedly “transited” in front of the brighter of its two stars using the TESS satellite telescope. This aided in estimating its size, which is around the same as Saturn, but not it’s mass.
In contrast, in the present study, the scientists were keeping an eye on this binary system by searching for jitters in the stars’ orbits. This “radial velocity” technique can identify a planet’s gravitational pull. This trembling can assist disclose a planet’s mass because a planet’s gravity is proportional to its mass.
It is challenging to find circumbinary planets using the radial velocity method
According to research co-author Amaury Triaud, an astronomer at the University of Birmingham in England, BEBOP-1c is the first circumbinary planet discovered using only the radial velocity method. Its discovery would have occurred sooner, however, COVID caused the observatories that assisted in the detection of BEBOP-1c to temporarily close their doors, postponing these discoveries for a year.
“Until now, circumbinary planets have been discovered in transit by the Kepler and TESS space telescopes, which cost hundreds of millions of dollars,” Standing said. This new discovery is powerful because it shows “you don’t need expensive space telescopes to detect these planets.” Instead, they can also be discovered using the radial-velocity technique “from ground-based telescopes with careful planning and target selection.”
It is challenging to find circumbinary planets using the radial velocity method. Standing said it can be difficult to gather exact data on the movements of both stars to validate the existence of circumbinary worlds.
“BEBOP gets around this problem by choosing binary stars where the secondary star is far smaller and dimmer than the primary star. This means that the secondary star isn’t seen by our telescopes and so the two signals don’t interfere,” Standing said. “These types of binary star systems are rarer than ones where the two stars are of similar size, but with recent advancements in data analysis techniques, BEBOP will expand its search to planets around these equal-size binaries in the near future.”
There are currently just two known worlds in the circumbinary TOI-1338/BEBOP-1 system. However, the experts noted that more might be discovered in the future. Future studies may also help to corroborate the dimensions and mass of TOI-1338b and BEBOP-1c.
“We have an ongoing survey with telescopes in France and Chile to find more circumbinary planets and measure their properties more accurately,” Triaud said. “For instance, how often do they happen; are they the same or less or more massive than planets orbiting single stars; and so on.”
A crucial next step, in Triaud’s words, “would be to measure the atmospheric chemistry of circumbinary planets and compare them to planets orbiting single stars,” is to learn more about these worlds’ atmospheric chemistry.
“Telescopes like the James Webb Space Telescope are uniquely suited for it and these types of investigations would provide very novel evidence about planet formation.”