NASA’s TESS spacecraft discovers its first habitable planet, first world with two stars

The planet, which is nearly seven times larger than Earth, lies in the constellation Pictor. Its two stars orbit each other every 15 days. One star is about 10% more massive than our sun, while the other is cooler, dimmer and only one-third the sun’s mass. 

TOI 1338 b, as it is now called, is TESS’s first circumbinary planet—the term for a world orbiting two stars. TOI 1338 b is the only known planet in the system; it orbits in almost exactly the same plane as the stars, so it experiences regular stellar eclipses. 

But 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,” said lead author Veselin Kostov, a research scientist at the SETI Institute and Goddard. “The human eye is extremely good at finding patterns in data, especially non-periodic patterns like those we see in transits from these systems.”

Luckily, high school senior Wolf Cukier was combing through data taken by TESS as a summer intern at Goddard.

“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 in our plane of view,” 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.”

After Cukier flagged TOI 1338 b, the research team used a software package called eleanor, named after Eleanor Arroway, the central character in the novel Contact by Carl Sagan (a UChicago alum), to confirm the transits were real and not a result of instrumental artifacts. 

“Throughout all of its images, TESS is monitoring millions of stars,” said Adina Feinstein, a graduate student at the University of Chicago. “That’s why our team created eleanor. It’s an accessible way to download, analyze and visualize transit data. We designed it with planets in mind, but other members of the community use it to study stars, asteroids and even galaxies.”

David Martin, who was a postdoctoral researcher at UChicago at the time of the discovery (now at Ohio State), noted that as they dug through the data, they found that TOI 1338 b had also been surveyed by a mission called BEBOP, which measures the wobble induced in stars by the mass of orbiting planets. This measurement, an entirely different type from TESS’s transit method, offers a complementary set of information. 

“We could combine the two types of data to get a much better characterization of the planet,” he said. “That’s one of the really cool things about TESS; it’s targeting bright, well-known stars, many of which have already been observed for years, even decades!”

In addition to Gilbert and Feinstein, other UChicago co-authors on the papers included Assoc. Prof. Daniel Fabrycky and Benjamin Montet, then a postdoctoral researcher at UChicago, now with The University of New South Wales. 

More than a dozen universities, research institutes and observatories worldwide are participants in the TESS mission.

—Adapted from two articles by Jeanette Kazmierczak originally posted on the NASA Goddard Space Flight Center website.