The planet, which the researchers believe is still growing, was glimpsed while scientists looked at the young double star CS Cha.
Double or binary stars are systems in which two stars are orbiting around each other – or technically around a special place in between both called the barycentre.
More details on their findings about the planet will soon be published in the journal Astronomy & Astrophysics.
The binary star CS Cha and the toddler planet are located 600 light years away from Earth in the southern hemisphere constellation Chameleon.
The star is just two to three million years old, and is at such an early stage in the development of its binary solar system that the scientists wanted to search for a dust disc and for planets being born.
How planets are formed is still not fully understood by scientists, and NASA recently launched a mission to Mars to help us learn why it is so different from Earth.
The planet was spotted by chance as the astronomers were investigating the binary star and noticed a dot at the edge of their images.
After diving into the archives of the telescope data, the scientists discovered the dot again in 19-year-old photographs taken with the Hubble Space Telescope, as well as in 11-year-old photographs from the Very Large Telescope.
These images helped prove that the companion dot was moving with the binary star system, although what it looks like and where it came from is not clear.
There is a chance that the companion is just a small brown dwarf star – but it could also be an enormous super-Jupiter style gas giant.
Lead author Christian Ginski of Leiden University explained: “The most exciting part is that the light of the companion is highly polarised.
“Such a preference in the direction of polaristion usually occurs when light is scattered along the way. We suspect that the companion is surrounded by his own dust disc.
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“The tricky part is that the disc blocks a large part of the light and that is why we can hardly determine the mass of the companion.
“So it could be a brown dwarf but also a super-Jupiter in his toddler years. The classical planet-forming-models can’t help us.”