A high school senior from Scarsdale in New York helped NASA’s planet hunter satellite TESS (Transiting Exoplanet Survey Satellite) discover a new intriguing planet that circles two stars and is about as large as Neptune or Saturn.
The student, Wolf Cukier, 17, was poring through data from TESS, archived at the Infrared Processing and Analysis Center (IPAC) at Caltech in Pasadena, when he saw something that caught his attention.
“I was looking through the data for everything the volunteers had flagged as an eclipsing binary, a system where two stars circle around each other and from our view eclipse each other every orbit,” Cukier said. “About three days into my internship, I saw a signal from a system called TOI 1338. At first I thought it was a stellar eclipse, but the timing was wrong. It turned out to be a planet.”
The planet, which Cukier now compares to Tatooine in the Star Wars film series, is the first of its kind for the TESS mission. Now called TOI 1338 b, the planet was found 1,300 light-years away in the Pictor constellation. It’s the only planet in the system with two stars and experiences regular eclipses from its stars. The smaller star circles the larger star which is over 10 times bigger than the sun.
Cukier was interning for NASA’s Goddard Space Flight Center over the summer when he spotted TOI 1338 b.
TESS has four cameras, which each take a full-frame image of a patch of the sky every 30 minutes for 27 days. Scientists use the observations to generate graphs of how the brightness of stars change over time. When a planet crosses in front of its star from our perspective, an event called a transit, its passage causes a distinct dip in the star’s brightness.
NASA said planets orbiting two stars (circumbinary) are more difficult to detect than those orbiting one. TOI 1338 b’s transits are irregular, between every 93 and 95 days, and vary in depth and duration thanks to the orbital motion of its stars. TESS only sees the transits crossing the larger star; the transits of the smaller star are too faint to detect.
“These are the types of signals that algorithms really struggle with,” Veselin Kostov, a research scientist at the SETI Institute and Goddard, said. “The human eye is extremely good at finding patterns in data, especially non-periodic patterns like those we see in transits from these systems.”
Cukier had to visually examine each potential transit. For example, he initially thought TOI 1338 b’s transit was a result of the smaller star in the system passing in front of the larger one – both cause similar dips in brightness. But the timing was wrong for an eclipse.
After identifying TOI 1338 b, the research team used a software package called eleanor, named after Eleanor Arroway, the central character in Carl Sagan’s novel “Contact,” to confirm the transits were real and not a result of instrumental artifacts.
NASA’s Kepler and K2 missions previously discovered 12 circumbinary planets in 10 systems, all similar to TOI 1338 b. Observations of binary systems are biased toward finding larger planets, Kostov said.
TESS is expected to observe hundreds of thousands of eclipsing binaries during its initial two-year mission. Many more of these circumbinary planets could simply be awaiting discovery.