European astronomers have discovered one of the smallest planets known outside our solar system, a world about 14 times the mass of our own. It could be a rocky planet with a thin atmosphere, a sort of "super Earth," the researchers said today.

But this is no typical Earth. It completes its tight orbit in less than 10 days, compared to the 365 required for our year. Its daytime face would be scorched.

It is not possible to know exact surface conditions of the planet, said Portuguese researcher Nuno Santos, who led the discovery. "However, we can expect it to be quite hot, given the proximity to the star."

Hot as in around 1,160 degrees Fahrenheit (900 Kelvin), Santos told SPACE.com.

Still, the discovery is a significant advance in technology: No planet so small has ever been detected around a normal star. And the finding reveals a solar system slightly similar to our own in ways not seen until now.

Terrestrial in nature

The star is like our Sun and just 50 light-years away. A light-year is the distance light travels in a year, about 6 trillion miles (10 trillion kilometers). Most of the known extrasolar planets are hundreds or thousands of light-years distant.

The star, mu Arae, is visible under dark skies from the Southern Hemisphere. It harbors two other planets. One is Jupiter-sized and takes 650 days to make its annual trip around the star. The other planet, whose existence was confirmed with the help of the new observations, is farther out.

Nearly all of the more than 120 planets found beyond our solar system are gaseous worlds as big or larger than Jupiter, mostly in tight orbits that would not permit a rocky planet to survive. Search techniques have so far not allowed the discovery of anything smaller than Saturn around Sun-like stars.

A trio of roughly Earth-sized planets was found in 2002 to orbit a dense stellar corpse known as a neutron star. They are oddballs, however, circling rapidly around a dark star that would not support life. Some planet hunters don't consider these three to be as important as planets around normal stars.

At 14 times the mass of Earth, the newfound planet -- circling a star similar in size and brightness to our Sun -- is about as heavy as Uranus, a world of gas and ice and the smallest giant planet in our solar system. Theorists say 14 Earth-masses is roughly the upper limit for a planet to possibly remain rocky, however. And because this planet is so close to its host star, it likely had a much different formation history than Uranus.

In our solar system, the four innermost planets are all rocky.

Rock and air

The leading theory of planet formation has the gas giants forming from a rocky core, a process in which the core develops over time, then reaches a tipping point when gravity can rapidly collect a huge envelope of gas. This theory suggests the newfound planet never reached that critical mass, said Santos, of the Centro de Astronomia e Astrofisica da Universidade de Lisboa, Portugal.

"Otherwise the planet would have become much more massive," Santos said via e-mail.

"This object is therefore likely to be a planet with a rocky core surrounded by a small gaseous envelope and would therefore qualify as a super-Earth," the European team said in a statement.

"This makes mu Arae a very exciting planetary system," said French researcher Francois Bouchy, another member of the search team.

The discovery was made with a European Southern Observatory telescope at La Silla, Chile. There are no conventional pictures of the object, as it was detected by noting it gravitational effect on the star. The search project leading to the discovery is led by Michel Mayor of the Geneva Observatory in Switzerland.

While researchers do not know the full range of conditions under which life can survive, the newly discovered world, with its hot surface, is not the sort of place biologists would expect to find life as we know it.

Santos said life on the large world is not likely. But, he added, "one never knows."

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