for National Geographic News
A Neptune-size planet likely covered in hot—but solid—water has been discovered in a snug orbit around a nearby star, a team of astronomers announced today.
While this planet is not fit for life, the finding suggests astronomers may soon detect habitable planets in similar alien solar systems, said Michaël Gillon of the University of Liège in Belgium.
"We are just at the door of a very exciting era," he said in an email interview.
The exotic water detected on the planet is known to form under extremely high pressure—conditions that can only be replicated on Earth in laboratories.
The planet, called GJ 436 b, orbits a cool, red star at a distance of only 2.5 million miles (4 million kilometers).
By contrast, Mercury, the innermost planet in our solar system, is 29 million miles (47 million kilometers) from the sun at its closest approach.
The "hot ice world" is about 30 light-years from the sun.
Four Times Earth's Size
GJ 436 b was first detected in 2004 by the way it tugs on its parent star during orbit. This telltale sign allowed astronomers to determine it is at least 22 times as massive as Earth.
Gillon and his colleagues re-examined the planet this year with several ground-based telescopes as the world passed in front of its host star.
This "transit" dims the light from the star, indicating the planet's presence.
Careful observations of the transit allowed the team to calculate the size of the planet —about four times the diameter of Earth—and also pinned its mass as 22 times that of Earth.
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