Photo by: NASA


A Jupiter-Sized Exoplanet Orbiting Two Stars

One of my favorite things about exoplanet systems is just how weird they can get. It seems that every few months we are treated to another surprise. This time around, NASA's TESS observatory delivered a planet almost three times more massive than Jupiter orbiting around not one, but two stars. As an added bonus: that planet orbits its twin suns closer than the Earth does around the sun. Who wants to take a trip?

July 26, 2021

Finding exoplanets -planets orbiting other stars - is pretty much routine nowadays. All you have to do is stare at stars long enough. If you're lucky, an exoplanet will have just the right orbit so that it crosses the face of its parent star as viewed from the Earth. We don't get to see the planet itself, but we do see the subtle dip in brightness from the exoplanet blocking some of its parent star’s light. With this technique, called the transit method, astronomers have discovered thousands upon thousands of worlds outside of our solar system.

And in the case of TIC 172900988b (I’m sorry it’s not a very romantic name, but that’s all we’ve got), astronomers saw this transit happen twice in the same observation. Staring at a star 824 light-years away in the direction of the constellation Cancer with NASA’s Transiting Exoplanet Survey Satellite (TESS), astronomers noticed the characteristic dip in brightness from an exoplanet crossing our line of sight. And then 5 days later, they saw the exact same thing happen again.

Illustration of NASA's Transiting Exoplanet Survey Satellite: TESS

Photo by: NASA's Goddard Space Flight Center

NASA's Goddard Space Flight Center

Illustration of NASA's Transiting Exoplanet Survey Satellite: TESS

The astronomers concluded that they found a case of a planet orbiting a binary star system, and the real treat was that this was the most massive known planet to do that.

And what a wonderful system it is. In the center of the system there are two stars orbiting each other every 19.7 days. And around them sits a giant planet, 2.9 times the mass of Jupiter. That giant planet has an orbit around the binary pair lasting around a couple hundred days. Placed in our own solar system for comparison, that would place that giant world just within the orbit of Venus.

The stars in the system make an eclipsing binary, which occurs when the stellar companions circle each other in our plane of view.

Photo by: NASA/Goddard Space Flight Center

NASA/Goddard Space Flight Center

The stars in the system make an eclipsing binary, which occurs when the stellar companions circle each other in our plane of view.

Imagine coming up on this world for yourself. You see a planet like Jupiter orbiting where Venus ought to be. And instead of a single star you have two stars rapidly rotating around each other.

It's better than anything any science fiction writer could possibly come up with, and the more we observe exoplanets the more we find out just how weird and wonderful our universe is.

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Paul M. Sutter

Paul M. Sutter is an astrophysicist at Stony Brook University and the Flatiron Institute, host of Ask a Spaceman and Space Radio, and author of How to Die in Space.

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