By Stephen Beech
An “extra exceptional” Tatooine-like exoplanet, orbiting two suns, has been discovered.
Astronomers say the “huge” new world is six times the size of Jupiter despite only forming 50 million years after the dinosaurs went extinct.
And it hugs its twin stars more tightly than any other directly imaged planet in a binary system.
While obtaining an image of a planet beyond our solar system is already rare, finding one that circles two suns is even rarer.
The new exoplanet is six times closer to its suns than other previously discovered exoplanets, according to a study published in The Astrophysical Journal Letters.
Many people are familiar with the iconic scene from the movie Star Wars when Luke Skywalker gazes up at the binary stars that his home planet Tatooine orbits.
Now, the new discovery provides an unprecedented look at how planets move and form around multiple stars.
Study senior author Dr. Jason Wang, of Northwestern University in Illinois, US, said: “Of the 6,000 exoplanets that we know of, only a very small fraction of them orbit binaries.
“Of those, we only have a direct image of a handful of them, meaning we can have an image of the binary and the planet itself.
“Imaging both the planet and the binary is interesting because it’s the only type of planetary system where we can trace both the orbit of the binary star and the planet in the sky at the same time.
“We’re excited to keep watching it in the future as they move, so we can see how the three bodies move across the sky.”
A team from Northwestern found the new exoplanet hidden within years-old data.
When Wang was a doctoral student, he helped commission the Gemini Planet Imager (GPI), a specialized instrument designed to capture images of distant worlds by blocking out the overwhelming glare of their stars.
Originally operated at the Gemini South telescope in Chile, GPI used adaptive optics and a coronagraph to sharpen images of faint planets orbiting bright stars.
Dr. Wang said: “We undertook this big survey, and I travelled to Chile several times.
“I spent most of my time during my Ph.D. just looking for planets.
“During the instrument’s lifetime, we observed more than 500 stars and found only one new planet.
“It would have been nice to have seen more, but it did tell us something about just how rare exoplanets are.”
Nearly a decade later, Dr. Wang asked study lead author Nathalie Jones to revisit the data.
He said: “I didn’t think we’d find any new planets.
“But I thought we should do our due diligence and check carefully anyway.”
Research fellow Jones analysed GPI data taken between 2016 and 2019 and cross-referenced it with data from the W.M. Keck Observatory.
She noticed something suspicious – a faint object appeared to be consistently following the motion of a star as it moved across the sky.
Dr. Wang said: “Stars don’t stand still in a galaxy, they move around.
“We look for objects and then revisit them later to see if they have moved elsewhere.
“If a planet is bound to a star, then it will move with the star.
“Sometimes, when we revisit a ‘planet,’ we find it’s not moving with its star.
“Then, we know it was just a photobombing star passing through.
“If they are both moving together, then that’s a sign that it’s an orbiting planet.”
Jones said: “We also look at the light coming off an object.
“We know what light from a star looks like versus what light from a planet looks like.
“We compared them and decided it better matched what we expect to see from a planet.”
To the team’s surprise, Jones verified the suspicious object was a planet, which GPI captured in 2016, but it had gone unnoticed in earlier analysis.
At around the same time, a European team led by University of Exeter astronomers independently found the same planet in its own reanalysis of the data, confirming Jones’ discovery.
While hotter than any planet in our solar system, it’s relatively cool compared to other directly imaged exoplanets.
It’s located around 446 light-years away from Earth, which Wang describes as “not within our local solar neighborhood but like the next town over.”
Having formed just about 13 million years ago, the new exoplanet is also quite youthful.
Dr. Wang said: “That sounds like a long time ago, but it’s 50 million years after dinosaurs went extinct.
“That’s relatively young in universe speak, so it still retains some of the heat from when it formed.”
The research team was also struck by how close the exoplanet orbited around its host stars.
The stars themselves tightly revolve around one another – taking just 18 Earth days to complete one revolution.
The planet, however, takes 300 years to orbit the pair. That’s a little longer than Pluto takes to orbit our sun.
Dr Wang said: “You have this really tight binary, where stars are dancing around each other really fast.
“Then there is this really slow planet, orbiting around them from far away.”
The Northwestern team don’t know how the system formed, but believe the binary stars formed first and then the planet formed around them.
Dr. Wang said: “Exactly how it works is still uncertain.
“Because we have only detected a few dozen planets like this, we don’t have enough data yet to put the picture together.”
The team plans to continue studying the system, so they can learn more about how it formed and how it works.
Jones said: “We want to track the planet and monitor its orbit, as well as the orbit of the binary stars, so we can learn more about the interactions between binary stars and planets.”
She is also continuing to reanalyse the old data, to see if previous astronomers missed anything else, adding: “There are a couple suspicious objects.
“But what they are, exactly, remains to be seen.”
