Planet 9 – the first exoplanet within our home solar system


The newest computer simulation, conducted by researchers from the Lund University in Sweden, suggests the so-called Planet 9 is most likely an exoplanet. If the discovery proves correct, it will make it the first exoplanet revealed inside our home solar system and, possibly, the only exoplanet we could reach by using a space probe.

Caltech scientists announced late January 2016 they have found evidence of a giant planet, 10 times the mass of Earth, tracing an unusual, highly elongated orbit, 20 times farther from the Sun than Neptune's in our outer solar system. And now it seems the large Planet 9 is, in fact, an exoplanet or an extrasolar planet, located outside of our solar system.

According to the experts from Lund, the planet was captured by our, at the time still young, Sun about 4.5 billion years ago, and had remained undetected so far.

"It is almost ironic that while astronomers often find exoplanets hundreds of light years away in other solar systems, there's probably one hiding in our own backyard," said Alexander Mustill, an astronomer at Lund University.

Video credit: Lund University

Stars are born in clusters and often pass by one another. During their encounter, it is possible that one star "steals" the planets that are orbiting the other star, and this may have happened to the Planet 9, as well, according to the computer simulation Alexander performed in cooperation with astronomers from Lund and Bordeaux.

"Planet 9 may very well have been 'shoved' by other planets, and when it ended up in an orbit that was too wide around its own star, our Sun may have taken the opportunity to steal and capture Planet 9 from its original star. When the Sun later departed from the stellar cluster in which it was born, Planet 9 was stuck in an orbit around the Sun," explained Alexander.

"There is still no image of Planet 9, not even a point of light. We don't know if it is made up of rock, ice, or gas. All we know is that its mass is probably around ten times the mass of Earth."

However, as exciting as the discovery may be, it will take further research to establish whether the Planet 9 is, indeed, the first exoplanet found in our solar system.

"This is the only exoplanet that we, realistically, would be able to reach using a space probe," Alexander concluded.


  • "Is there an exoplanet in the Solar System?" – Alexander J. Mustill1, Sean N. Raymond, and Melvyn B. Davies – Monthly Notices Letters of the Royal Astronomical Society (2016) – doi: 10.1093/mnrasl/slw075

Featured image credit: Lund University


Commenting rules and guidelines

We value the thoughts and opinions of our readers and welcome healthy discussions on our website. In order to maintain a respectful and positive community, we ask that all commenters follow these rules.

One Comment

Leave a reply

Your email address will not be published. Required fields are marked *