Planets beyond our solar system

Shortly after NASA’s Kepler mission began operating in 2009, the space telescope spotted what was believed to be a planet about half the size of Saturn in a multi-star system. KOI-5Ab was only the second candidate planet to be found by the mission, and exciting as it was at the time, it was eventually set aside as Kepler amassed more and more discoveries from the planet.

By the end of the spacecraft’s operations in 2018, Kepler had discovered a whopping 2,394 exoplanets or planets orbiting stars beyond our sun and an additional 2,366 exoplanet candidates that would still need confirmation.

“The KOI-5Ab was abandoned because it was complicated and we had thousands of candidates,” said David Ciardi, chief scientist at NASA’s Exoplanet Science Institute. “There were easier selections than KOI-5Ab and every day we learned something new from Kepler, so KOI-5 was mostly forgotten.”

Now, after a long hunt that spanned many years and many telescopes, Ciardi said he has “resurrected KOI-5Ab from the dead.” Thanks to new observations from NASA’s second planetary hunting mission, the Transiting Exoplanet Survey Satellite, or TESS, and several ground-based telescopes, Ciardi was able to unravel all the evidence surrounding the KOI-5Ab and prove its existence. . There are some interesting details on this topic for reflection.

Most likely, a gas giant planet like Jupiter or Saturn in our solar system given its size, KOI-5Ab is unusual in the fact that it orbits one star in a system with two other companion stars, orbiting a plane that is outside. of alignment with at least one. of the stars. The arrangement calls into question how each member of this system was formed from the same clouds of gas and swirling dust. Ciardi, who is at Caltech in Pasadena, California, presented the findings at a virtual meeting of the American Astronomical Society.

Picking up the trail

After their initial detection by Kepler, Ciardi and other researchers picked up the trail on KOI-5Ab as part of a cache of candidates on the planet they were following. Using data from the WM Keck Observatory in Hawaii, the Caltech Palomar Observatory near San Diego, and the Gemini North in Hawaii, Ciardi and other astronomers determined that the KOI-5b appeared to circle a star in a three-star system. . However, they could not yet test whether the planet’s signal was actually a wrong error from one of the other two stars or, if the planet was real, which of the stars was orbiting.

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

“I thought‘ I remember that goal, ’” Ciardi said, after seeing the TESS data. “But we still couldn’t definitively determine if the planet was real or if the data information came from another star in the system: it could have been a fourth star.”

Tracks on the swings

He then went back and re-analyzed all the data and then looked for new clues from ground-based telescopes. Deploying an alternative technique to Kepler and TESS, the Keck Observatory is often used to search for exoplanets by measuring the slight oscillation of a star as a planet revolves around it and exerts a gravitational pull. Ciardi, teaming up with other scientists through a collaborative group with exoplanets called California Planet Search, looked for any oscillation in Keck’s data on the KOI-5 system. They were able to eliminate an oscillation produced by the inner companion star that orbits the primary star from the oscillation of the apparent planet as it orbits the primary star. Together, the various data collections from terrestrial 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 gone back and done all this detective work, “he said. But it really needed a lot of research into the data collected from many different telescopes to finally nail them to this planet. “

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.

A skewed orbit

The combined dataset also reveals that the planet’s orbital plane is not aligned with the orbital plane of star B, the second inner star as one might expect if the stars and the planet formed from the same disk of material that swirl. Astronomers are not sure what caused the misalignment of KOI-5Ab, but believe that the second star gravitationally hit the planet during its development, skewing its orbit and causing it to migrate inward. Three-star systems account for approximately 10% of all star systems.

This is not the first evidence of planets in double and triple star systems. A striking case is the three-star GW Orionis system, in which a planet-forming disk has been broken into different misaligned rings, where planets can form. However, despite the hundreds of planetary discoveries in multi-star systems, far fewer planets have been observed than in single-star systems. This could be due to an observational bias (single-star planets are easier to detect), or because planet formation is in fact less common in multi-star systems.

“This research highlights the importance of NASA’s entire fleet of space telescopes and their synergy with terrestrial systems,” said Jessie Dotson, the scientist for the Kepler space telescope at NASA’s Ames Research Center in Silicon. California Valley. “Discoveries like this can be a long journey.”

New and future instruments, such as the Palomar radial velocity instrument in the 200-inch Hale telescope in Palomar, the NASA NEID instrument and the National Science Foundation in southern Arizona, and the Keck Planet Finder will open new avenues for discovering the exoplanets.