Using an infrared camera, astronomers at the University of Montreal have discovered and directly imaged GU Psc b, a planet with a mass 10 times greater than Jupiter's and orbiting its star at 2,000 times the distance between Earth and our sun. This very rare find will encourage scientists to start looking for exoplanets in places where, thus far, they hadn't even thought to look.

Current theories predict that the vast majority of planets orbit their star at a distance up to 100 astronomical units (AU) – that is to say, one hundred times the distance between Earth and our sun. So, in their search for exoplanets, astronomers have mostly focused well within this boundary. They detect new planets indirectly by looking at how they affect their star's gravitational field or, very rarely, by imaging them directly with infrared light, using adaptive optics to tell them apart from their own star.

A research team led by PhD student Marie-Ève Naud set out to look for distant planets with a new approach. Using an infrared camera, Naud and colleagues attempted to detect new planets directly, without adaptive optics, and looking well beyond the usual 100 AU boundary. To do so, they relied on patterns of infrared wavelengths that distinguish planets from galaxies and other celestial bodies. After surveying dozens of stars in this way, they finally laid their eyes on GU Psc b, a planet 155 light years away from our solar system, in the Pisces constellation.

What they saw puzzled them. As they soon found out, the planet GU Psc b is a huge gas giant orbiting around a small star with a mass only one third that of our sun, at a distance of 2,000 AUs and with a revolution period of 80,000 Earth years.

"It’s not a type of exoplanet we had previously found and it's certainly not one that the theorists were expecting, especially not around low-mass stars like GU Psc," said Naud.

With a mass 9 to 13 time greater than that of Jupiter and a surface temperature of around 800° C (1500° F), the planet is close to the critical mass beyond which a gas giant begins to experience nuclear fusion reactions in its core to become a brown dwarf.

According to the researchers, GU Psc b is a true diamond in the rough. Because it is so far from its own star, it can be studied in detail without the danger of nearby celestial bodies interfering with the measurements. This will allow astronomers to better characterize giant exoplanets and learn where and how they can find more of the same type.

Using the data they've gathered, the scientists have already started observing hundreds of stars looking for planets that are smaller than GU Psc, but orbiting at similar distances. Then, in the near future, they will switch to looking for giant exoplanets similar to GU Psc, but which are orbiting much closer to its star.

A study detailing the discovery was recently published in The Astrophysical Journal.

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