NASA’s TESS mission uncovers its first world with two stars

NASA/Goddard Space Flight Center

 TOI 1338 b is silhouetted by its host stars. TESS only detects transits from the larger star. Credit: NASA's Goddard Space Flight Center/Chris Smith

TOI 1338 b is silhouetted by its host stars. TESS only detects transits from the larger star. Credit: NASA’s Goddard Space Flight Center/Chris Smit

In 2019, when Wolf Cukier finished his junior year at Scarsdale High School in New York, he joined NASA’s Goddard Space Flight Center in Greenbelt, Maryland, as a summer intern. His job was to examine variations in star brightness captured by NASA’s Transiting Exoplanet Survey Satellite (TESS) and uploaded to the Planet Hunters TESS citizen science project.

“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.”

TOI 1338 b, as it is now called, is TESS’s first circumbinary planet, a world orbiting two stars. The discovery was featured in a panel discussion on Monday, Jan. 6, at the 235th American Astronomical Society meeting in Honolulu. A paper, which Cukier co-authored along with scientists from Goddard, San Diego State University, the University of Chicago and other institutions, has been submitted to a scientific journal.

The TOI 1338 system lies 1,300 light-years away in the constellation Pictor. The two stars orbit each other every 15 days. One 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 is the only known planet in the system. It’s around 6.9 times larger than Earth, or between the sizes of Neptune and Saturn. The planet orbits in almost exactly the same plane as the stars, so it experiences regular stellar eclipses.

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.

But planets orbiting two stars 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,” 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.”

This explains why 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.

“Throughout all of its images, TESS is monitoring millions of stars,” said co-author 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.”

TOI 1338 had already been studied from the ground by radial velocity surveys, which measure motion along our line of sight. Kostov’s team used this archival data to analyze the system and confirm the planet. Its orbit is stable for at least the next 10 million years. The orbit’s angle to us, however, changes enough that the planet transit will cease after November 2023 and resume eight years later.

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. Transits of smaller bodies don’t have as big an effect on the stars’ brightness. TESS is expected to observe hundreds of thousands of eclipsing binaries during its initial two-year mission, so many more of these circumbinary planets should be waiting for discovery.


TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA’s Goddard Space Flight Center. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT’s Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.?

Banner: TOI 1338 b is silhouetted by its host stars. TESS only detects transits from the larger star. Credit: NASA’s Goddard Space Flight Center/Chris Smith

By Jeanette Kazmierczak
NASA’s Goddard Space Flight Center, Greenbelt, Md.

Media contact:

Claire Andreoli
NASA’s Goddard Space Flight Center, Greenbelt, Md.

From EurekAlert!

39 thoughts on “NASA’s TESS mission uncovers its first world with two stars

    • I remember the sunsets on Tatooine, as if it were yesterday…. or something. Well, it was a while back, anyway.

    • Forget Tatooine and other such juvenilia. The real hero of binary star science-fi is Fredric Brown whose short story ‘Placet is a crazy place’ is a wonderfully-plotted and beautiful example of the genre.

      If you have not read it, I urge you to track it down and spend 10 hugely entertaining and amusing minutes reading this perfectly-crafted gem. It also contains one of the best examples of getting hold of the wrong end of the stick in 20th century science fiction.

      I think this newly-found planet in its binary star system should be named Placet in his honour.

  1. So, this planet, TOI 1338 b, if it has oceans, must have 500 meter high tides, and people regularly weigh 20 lilos or 300 kilos, and the inhabitants, commonly known as #$=?$%&wookies, are in the final phase of destroying their planet due to CO2 emissions, and we should send Algore directly there, no matter the distance, to try to save them? Otherwise this is nothing more than a trivial footnote in the universe.

  2. I guess the planet is too small to offer a solution to the 3 body gravitational problem or has this mathematical problem already been solved?

    • One pair of binary stars with a large planet orbiting gives a problem with taking the initial positions and velocities (or momenta)

      – of three point masses

      and solving for their subsequent motion.

      “In physics and classical mechanics, the three-body problem is the problem of taking the initial positions and velocities (or momenta) of three point masses and solving for their subsequent motion according to Newton’s laws of motion and Newton’s law of universal gravitation.[1]”

  3. This is the TESS team’s first observation of such a system.

    “NASA’s Kepler and K2 missions previously discovered 12 circumbinary planets in 10 systems, all similar to TOI 1338 b.”

    Find me a Earth-size exoplanet around a unitary G1-G4 class star in the “habitable zone” please.
    A system where the gas giants stayed beyond the frost line to mostly deflect the inner planets from comets.
    Then does it have a large moon? (effectively Earth and Luna are a binary planet system, probably exceedingly rare in its own right)
    Then does the earth-size rocky exoplanet have an oxygen spectral line and a blue appearance?

    Until then, just a lot of dead rocks out there getting either baked by hard radiation or cryogenically frozen.

  4. Did anyone see this that Ned Nikolov just tweeted?:

    Black Hole theory was never my favourite, as they are neither black nor holes.
    Hawking Radiation will never be or likely to be detected either!

    An interesting critique of the first “black hole” image recently claimed to have been recorded by radio-telescopes. It appears that astronomers fabricate data just like climate scientists do to promote their favourite theory about the Universe:

    • Interesting.

      The big difference between the Climate Experts and the Astrophysicists would be the level of smarts required to gain meaningful entry to the field ?

      In the video above, are there maybe 10,000 folk worldwide who could address the facts contained in a knowledgeable manner ? With Climate Science as presented to the public the bar to entry is so low that really its a game anybody can join. 🙂

  5. Fascinating! What are the odds that the orbits of both suns of a binary system, and a major planet, lie in a plane close enough to the earth that we can observe regular eclipses? What does that say about the probability of systems like this in the galaxy/universe?

    • TESS is collecting data on many millions of star systems. So it will statistically find many edge-on viewed systems.

  6. If the two stars orbit each other every 15 days, and the planet orbits both of them every 95 days, then the smaller star is much closer to the larger star than the planet is to either star. If the larger star is 10% more massive than the Sun, and the planet orbits every 95 days, its distance from the larger star would be similar to that of Mercury from our Sun, which orbits every 88 days.

    If we assume that the radiant energy from a star is proportional to its mass, this planet TOI 1338 b would receive a similar amount of radiation from the larger star as Mercury receives from the Sun, meaning that it would be extremely hot on the side facing the star. However, since this planet is larger than Neptune, it would have a much stronger gravity than Earth, so it may be able to retain a gaseous atmosphere despite its proximity to the larger star.

    It is possible that other planets orbit this pair of stars, although they would be more difficult to detect if they are smaller, farther from the larger star, and/or outside the orbital plane of TOI 1338 b. It would be interesting if a planet was found orbiting about 100 million miles from the larger star…

    • TESS is biased to find both fast orbiting and large exoplanets. It would take a decade or more of data to detect an exoplanet like Earth at 1 AU from a solar mass star, if it could see it even at all due to extremely low dimming signal on Earth against the Sun at 100 Ly. Probably not detectable agaisnt solar cycles and other transits from Venus etc.

      TESS really isn’t geared to find an Earth like exoplanet. It will allow statistical approaches to be used to assess how many stars in our galaxy have explanets. The answer ts probably “all of them.” in fsome form or another.

    • “It would be interesting if a planet was found orbiting about 100 million miles from the larger star…”

      That would be interesting.

      So this solar system has an F-type main star and a K-type secondary. We have found that M-type stars produce lots of solar flares, probably making planets orbiting them uninhabitable. As far as flares go, how does an F-type and a K-type star compare to a G-type star like our home star?

      Star types from the hottest to the coolest: OBAFGKM Oh, Be A Fine Girl, Kiss Me! I guess that would be considered sexist by some nowadays. But not by me. 🙂

      • You forgot the last two (both dwarves) R and N [making the mnemonic out to be Oh Be A Fine Girl Kiss Me Right Now]

    • We have an n=1 example of life on 1 planet. We have no idea (from 0 to infinity) what the real range is on most of the variables in the equation. That still tells us nothing about the answer.

    • The Drake Equation is practically useless.

      Since more then 100 years we have radio:

      “The Drake equation is used to estimate the number of technical, intelligent civilizations in our galaxy , the Milky Way.”

      A technical, intelligent civilization in any case would emit signals, e.g. radio signals – at the speed of light.

      – when we first hear from that civilization e.g. “via radio” said civilization is min. 100 light years away from us. A long distance for a real, material civilization – at magnitudes slower speed than light.

  7. Helen Sharman, the first Briton to go into space: “Aliens exist and could be here on Earth. It’s possible they’re right here right now and we simply can’t see them.”
    Clear case of the cerebrum cogitamentum radiative forced induction by the KGB during her visit to the Mir space station in May 1991. 🙂

  8. Actually n=0 since n= number of EXTRATERRESTIAL civilizations.

    So, Drake invented postmodern science by formulating an equation with 7 variables and ZERO empirical data points.

    Shame on him.

  9. That system is certainely not to compare with the Sirius A, B, C, where C is probably not a planet, and if it is, than it rotates only around A or B, isn’t ?

  10. Pretty. Inference from signals of unknown fidelity. It will be meaningful when we possess the skill to travel beyond our solar system, clear the dark and brown matter, and fill in the missing links.

  11. Gary Pearse, believe it or not –

    Hans Erren January 9, 2020 at 10:00 pm

    claims to already have mathematical solved the 3 body gravitational problem.

    For 2 suns and a small planet.

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