Icy 'super-Earth' around distant star
A cold, heavy 'super-Earth' has been found orbiting a distant star, using a method that holds promise for detecting faraway planets that closely resemble our own, astronomers say.
The planet weighs 13 times as much as Earth and is orbiting a star about 9000 light-years away.
But instead of circling close to its star, as Earth does, this super-Earth is about as distant from its star as Jupiter and Saturn are from the Sun.
An international team of scientists says the new planet probably has a temperature of minus 201°C, making it one of the coldest planets detected outside our solar system.
The discovery is billed as a super-Earth because it is thought to be a rocky, terrestrial planet like Earth, even though it is much more massive.
The planet was detected by astronomers using a project called OGLE, short for Optical Gravitational Lensing Experiment, which looks for changes in light coming from distant stars.
If another star passes between the faraway star and a telescope on Earth, the gravity of the intervening star acts like a lens and magnifies the incoming light.
When a planet is orbiting the closer star, the planet's gravity can add its own distinctive signature to the light.
This phenomenon is known as gravitational microlensing, and it has the potential to detect less massive planets than other methods of searching for planets around other stars.
Lots of super-Earths
The OGLE project detected the microlensing event in April; a total of 36 astronomers working with OGLE found the signs of a planet, 9000 light-years away in the direction of the Milky Way's central galactic bulge.
A light-year is about 10 trillion kilometres, the distance light travels in a year.
Professor Andrew Gould of Ohio State University who heads the planet-hunting group MicroFUN, short for Microlensing Follow-Up Network, says this discovery has two implications.
"First, this icy super-Earth dominates the region around its star that in our solar system is populated by the gas-giant planets, Jupiter and Saturn," Gould says.
"We've never seen a system like this before, because we've never had the means to find them.
"And second these icy super-Earths are pretty common. Roughly 35% of all stars have them."
In the past decade, scientists have detected some 170 so-called extrasolar planets, using a variety of techniques. The vast majority are gas giant planets like Jupiter that are hostile to life as it is known on Earth.
In January, a planet about five-and-a-half times Earth's mass circling a star near the center of the Milky Way was detected using gravitational microlensing.