Planetary research finds a world of three suns

This illustration shows the planet KOI-5Ab transiting the face of a Sun-like star, which is part of a triple star system located 1,800 light-years away in the constellation Cygnus. – CALTECH/R. HURT


New observations of a planet candidate from the Kepler mission have revealed that it orbits a star in a triple system, circling in a misaligned plane with at least one of them.

Most likely a gas giant like Jupiter or Saturn in our solar system given its size, KOI-5Ab is unusual in that the arrangement of its star system calls into question how each member of it formed from the same swirling clouds of gas and dust.

David Ciardi, chief scientist at NASA’s Institute for Exoplanet Sciences, presented the findings of the study of this alien world with the TESS mission at a virtual meeting of the American Astronomical Society.

“We don’t know of many planets that exist in triple star systems, and this one is very special because its orbit is skewed,” Ciardi said in a statement. “We still have many questions about how and when planets in multiple-star systems can form and how their properties compare to those of planets in single-star systems. By studying this system in greater detail, perhaps we can understand how the universe forms planets “.

After its initial detection by Kepler, Ciardi and other researchers followed the KOI-5Ab trail as part of a cache of planet candidates they were tracking. Using data from the WM Keck Observatory in Hawaii, Caltech’s Palomar Observatory near San Diego, and Gemini North in Hawaii, Ciardi and other astronomers determined that KOI-5b appeared to be circling a star in a triple star system. However, they were still unable to determine whether the planet’s signal was actually a faulty glitch from one of the other two stars or, if the planet was real, which of the stars it orbited.

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Then in 2018, TESS appeared. Like Kepler, TESS looks for the flicker of starlight that occurs when a planet crosses in front of, or transits, a star. TESS observed a portion of Kepler’s field of view, including the KOI-5 system. Sure enough, TESS also identified KOI-5Ab as a candidate planet, although TESS calls it TOI-1241b. As Kepler had previously observed, TESS discovered that the planet orbited its star approximately every five days.

“I thought to myself, ‘I remember this goal,'” Ciardi said, after looking at the TESS data. “But we still couldn’t definitively determine if the planet was real or if the flare in the data came from another star in the system, it could have been a fourth star.”

Then he went back and re-analyzed all the data, and then looked for new ground-based telescope leads. Implementing an alternative technique to Kepler and TESS, the Keck Observatory is often used for tracking searches for exoplanets by measuring the slight wobble in a star when a planet rotates around it and exerts a gravitational pull.

Ciardi, partnering with other scientists through an exoplanet collaborative group called the California Planet Search, looked for any oscillations in Keck’s data in the KOI-5 system. They were able to detect a wobble produced by the inner companion star orbiting the primary star from the apparent planet’s wobble as it orbits the primary star. Together, the different data collections from ground and space telescopes helped confirm that KOI-5Ab is, in fact, a planet orbiting the primary star.

“Bingo – it was there! If it weren’t for TESS looking at the planet again, I would never have come back and done all this detective work,” he said. “But it really took a lot of research into the data collected from many different telescopes to finally nail on this planet. “

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KOI-5Ab orbits star A, which has a relatively close companion, star B. Star A and star B orbit each other every 30 years. A third gravitationally bound star, Star C, orbits stars A and B every 400 years.

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