Astronomers have located an exoplanet they say is a long lost -- and long way away -- twin brother of Uranus, kind of. Until the new discovery, Uranus and Neptune were the only known "ice giants" in the Milky Way galaxy. Not any more, Ohio State researchers say.
Most planets are either rocky and solid, like Earth, or composed entirely of gas, like Saturn or Jupiter. Uranus, on the other hand, is both -- with a mostly gaseous outer layer and a rock-and-ice core. And while Uranus will remain cold and distant, it may not be as lonely, knowing it's got at least one twin sibling out there somewhere.
The newly discovered other Uranus is some 25,000 light years away, so astronomers can't exactly get a closeup. Thus, they can't be exactly sure of its composition. But because of its distance from its host star and its size, they estimate that it's quite similar to the light blue ice giant back home.
In fact, that astronomers can see this unusual exoplanet at all is quite lucky; it relies on a nifty little process called microlensing.
"Only microlensing can detect these cold ice giants that, like Uranus and Neptune, are far away from their host stars," Radek Poleski, a postdoctoral researcher at Ohio State University, said in a recent press release. "This discovery demonstrates that microlensing is capable of discovering planets in very wide orbits."
Microlensing is what happens in a binary star solar system when the light of one star (the one farther away from Earth) is bent by the gravity of the other, magnifying it like a lens. Occasionally, an orbiting planet will pass through this lens and become magnified inside the light beams, allowing astronomers to see what would normally be invisible.
Researchers say the binary star system (and its subsequent microlensing) didn't just allow them to see a hart-to-spot exoplanet, it offered clues as to how ice giants come to exist in the first place.
"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," explained Andrew Gould, an astronomy professor at Ohio State. "One idea is that they did form much closer, but were jostled around by Jupiter and Saturn and knocked farther out."
Gould says this new Uranus, the long lost twin, may offer credence to that idea.
"Maybe the existence of this Uranus-like planet is connected to interference from the second star," he said. "Maybe you need some kind of jostling to make planets like Uranus and Neptune."
The discovery of the faraway Uranus was detailed online this week in The Astrophysical Journal.