The first known exoplanet resembling Uranus in our own solar system has been detected orbiting a distant star 25,000 light years from earth, astronomers report.
Orbiting a double star system, the planet was detected with a technique known as microlensing, where the ability of massive stars to bend light can magnify objects behind them.
In a rare event, a planet around the lensing star can sometimes be detected within that magnified light signal, the researchers explain.
"Only microlensing can detect these cold ice giants that, like Uranus and Neptune, are far away from their host stars," says study leader Radek Poleski of Ohio State University. "This discovery demonstrates that microlensing is capable of discovering planets in very wide orbits."
Hundreds of exoplanets have been discovered to date, some rocky planets like the Earth, Mars or Venus, and some gas giants like Jupiter and Saturn, but the newly discovered world is the first found that resembles the third kind of planet orbiting in our solar system -- the "ice giants" Uranus and Neptune, part ice and part gas.
The distance of the exoplanet from its parent star suggests it's likely such an ice giant, possessing an orbit resembling that of Uranus, so it's considered an analog of the blue icy world in our solar system, an international team reported in The Astrophysical Journal.
Such ice giants are largely hydrogen and helium, but methane on their surfaces will freeze in cold temperatures, resulting in the characteristic blue appearance seen on Uranus and Neptune.
The discovery of the distant exoplanet may tell us more about the formation and of our solar system's own ice giants, researchers say.
"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," says research team member Andrew Gould. "One idea is that they did form much closer, but were jostled around by Jupiter and Saturn and knocked farther out."
Such jostling may be at work as the exoplanet orbits one star in the binary system but is close enough to the other for its orbit to be disturbed.
"Maybe the existence of this Uranus-like planet is connected to interference from the second star," Gould says. "Maybe you need some kind of jostling to make planets like Uranus and Neptune."
