A group of researchers has discovered a new exoplanet that is unique because it’s orbiting a pair of stars. A planet of this type is called circumbinary, and for many years the planets were theorized but hadn’t been discovered. The discovery of circumbinary planets was enabled thanks to powerful instruments such as the Kepler space telescope and the Transiting Exoplanet Survey Satellite (TESS). So far, astronomers have detected 14 circumbinary exoplanets.
According to researcher Nader Haghighipour, discovering a circumbinary planet is significantly more difficult than detecting exoplanets orbiting individual stars. One of the best ways to discover exoplanets orbiting binary stars is a technique called transit photometry, able to measure a decrease in starlight caused when planets orbiting a distant star pass between the star and the telescope observing it. At least three transits are required to determine the orbital path of the planet.
It’s more complicated to identify exoplanets when they orbit a pair of stars because transits don’t happen over the same intervals as they do for planets orbiting single stars. Kepler is particularly well-suited to discover exoplanets orbiting binary stars because it views one region in the sky for 3.5 years at a time. However, TESS isn’t well-suited for discovering exoplanets around binary stars because it only observes a portion of the sky for 27 days.
Researchers have invented a new technique to discover circumbinary planets utilizing TESS. Utilizing the new procedure, study authors can demonstrate during the TESS 27-day observation window if the planet showed two transits, moving in front of each star in the binary once. Utilizing that technique, the astronomers detected an exoplanet orbiting a binary called TIC 172900988.
The binary was observed in a single sector by TESS after its light curve showed two transits, with one across each star during the same conjunction. The project allowed the astronomers to show it was possible to use TESS data to detect circumbinary planets. The discovery of the planet orbiting the binary proves the validity and success of the new technique. In this instance, the exoplanet passed in front of the primary star, and then five days later passed in front of the second star. The stars in the binary are almost identical in size and are about 30 percent larger than the sun.
The newly discovered planet is called TIC 172900988b, and it’s about the same diameter as Jupiter but several times more massive. It orbits the binary in less than one year. Astronomers on the project see the planet as extremely hot and vastly different from anything in our solar system.
Astronomers have been working to detect exoplanets for a long time and have discovered many. Last month, astronomers discovered an exoplanet candidate in Messier 51. What was notable about that discovery is that it was the first exoplanet discovered transiting a star outside the Milky Way. The exoplanet is a galaxy about 28 million light-years away.
In August 2021, astronomers announced the discovery of a new type of potentially habitable exoplanet. The new type of habitable planet is known as a “Hycean” planet. Planets of this type are covered entirely by ocean and feature hydrogen-rich atmospheres. Project researchers believe Hycean planets are more numerous and easier to observe than planets like Earth. Astronomers have identified multiple Hycean candidates, all larger and warmer than Earth, with the potential to support microbial life.