This is the first time anyone has spotted a twin for our so-called 'ice giant' planets, Uranus and Neptune.
    
While Uranus and Neptune are mostly composed of hydrogen and helium, they both contain significant amounts of methane ice, which gives them their bluish appearance.
    
Given that the newly discovered planet is so far away, astronomers can't actually tell anything about its composition.
    
But its distance from its star suggests that it's an ice giant and since the planet's orbit resembles that of Uranus, the astronomers are considering it to be a Uranus analog.     

The newly discovered planet leads a turbulent existence: it orbits one star in a binary star system, with the other star close enough to disturb the planet's orbit.
    
The find may help solve a mystery about the origins of the ice giants in our solar system, said Andrew Gould, professor of astronomy at Ohio State University.
    
"Nobody knows for sure why Uranus and Neptune are located on the outskirts of our solar system, when our models suggest that they should have formed closer to the Sun," Gould said.    

"One idea is that they did form much closer, but were jostled around by Jupiter and Saturn and knocked farther out.
    
"Maybe the existence of this Uranus-like planet is connected to interference from the second star. Maybe you need some kind of jostling to make planets like Uranus and Neptune," he said.
    
The binary star system lies in our Milky Way galaxy, in the direction of Sagittarius. The first star is about two thirds as massive as our Sun, and the second star is about one sixth as massive.
    
The planet is four times as massive as Uranus, but it orbits the first star at almost exactly the same distance as Uranus orbits our Sun.
    
An international research team led by Radek Poleski, postdoctoral researcher at The Ohio State University, spotted the solar system due to a phenomenon called gravitational micro lensing when the gravity of a star focuses the light from a more distant star and magnifies it like a lens.
    
Very rarely, the signature of a planet orbiting the lens star appears within that magnified light signal.
    
In this case, there were two separate micro lensing events, one in 2008 that revealed the main star and suggested the presence of the planet, and one in 2010 that confirmed the presence of the planet and revealed the second star.
    
Both observations were done with the 1.3 metre Warsaw Telescope at Las Campanas Observatory in Chile as part of the Optical Gravitational Lensing Experiment (OGLE).     

The study was published in The Astrophysical Journal.

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