Scientists using NASA’s Transiting Exoplanet Survey Satellite (TESS) telescope have used a new method to find an unusual planet that orbits two stars. The planet TIC 172900988b has two stars, making it a type of planet called a circumbinary, and it is the first-of-its-kind to be discovered using TESS observing two transits.
Exoplanets, or planets outside our solar system, are usually too small to be observed directly. But scientists can infer their existence with the help of several techniques including transits. A transit is an event when an exoplanet passes between Earth and its sun, temporarily blocking out some of the star’s light. Astronomers look for such drops in light and use them to predict the presence of a planet.
Process gets difficult in this particular case
However, this is more complex when a planet orbits two stars, as one of the researchers who found out this planet, Planetary Science Institute Senior Scientist Nader Haghighipour explained:
“Detecting circumbinary planets is much more complicated than detecting planets orbiting single stars,” Haghighiour said. “The most promising technique for detecting circumbinary planets is transit photometry, which measures drops in starlight caused by those planets whose orbits are oriented in space such that they periodically pass between their stars and the telescope. In this technique, the measurements of the decrease in the intensity of the light of a star are used to infer the existence of a planet.
Two transits helped discover the planet
“To determine the orbit of the planet, precisely, at least three transit events are required. This becomes complicated when a planet orbits a double-star system because transits will not happen with the same interval over the same star. The planet may transit one star and then transit the other before transiting the first star again, and so on.”
The issue here is that three transits can take a long time – and TESS only observes a given portion of the sky for 27 days, which is less time to observe three transits. But in the case of TIC 172900988b, a planet having a size similar to Jupiter, the team managed to detect it with the help of just two transits — one transit of each of its host stars.
