I found this when having a gander at new scientist, its about Extrasolar planets. and it's pretty interesting, dunno if aliens could survive on this thing though.
Astronomers have found an extrasolar planet with the largest solid core ever detected. The core is so immense - as massive as 70 Earths - that astronomers believe it might have formed through collisions with other planets.
The planet was discovered around a star called HD 149026, which is rich in elements heavier than hydrogen and helium. Such "metal-rich" stars are three times more likely than their Sun-like cousins to harbour detectable planets.
Astronomers using Japan's powerful Subaru Telescope in Hawaii first detected the planet, called HD 149026b, in July 2004 by the gravitational tugs it exerted on its host star. Subsequent measurements taken by the Keck Observatory in Hawaii confirmed the star's resultant wobble, revealing the planet orbits its star every 2.87 days.
But in May 2005, astronomers using a relatively small robotic telescope in Arizona noticed a 0.3% dip in the star's brightness every 2.87 days. That dimming showed the planet was among an elite group of eight which are known to pass directly between their host stars and Earth during their orbits. Such transits can reveal the planet's exact physical size and mass, from which its density can be calculated.
“Weird object”
The results were surprising. The planet's diameter was about three-quarters that of Jupiter. But its density suggested that half to two-thirds of its mass was locked in heavy elements - mostly in a solid core.
That differs strikingly from other transiting extrasolar planets which, like Jupiter, are mostly hydrogen and helium gas with no more than a quarter of their mass taken up by their cores."This is a very weird object," says team member Greg Laughlin, an astronomer at the University of California in Santa Cruz, US.
Indeed, the discovery strains the two main planet-formation theories. In the “core accretion model”, planets form in a snowball effect by gradually building up a rocky core as a result of random collisions. The increasing gravity of the growing core then begins to attract more material and the gases that make up an atmosphere.
In the alternative “gravitational instability model”, gas giant planets form quickly by condensing directly from a cloud of gas and dust surrounding a young star.
Pushed to the limit
"We have no rigorous model for how this planet formed," Laughlin told New Scientist. He says gas giants in the gravitational instability model could gain heavy elements through collisions with comets or asteroids, but would not be able to swallow enough material to explain this observation.
"I'm a long-term cheerleader for the core accretion model," he says. "But this really pushes the model to its limits."
Laughlin says the new discovery suggests "something extra", such as a collision with one or more planets in the past, could explain the dense core. If so, the collision might have knocked the planet out of the star's equatorial plane. Astronomers have re-observed the star to check its axis of rotation and are currently processing this data.
Inward migration
The planet is a scalding 1200°C and lies about 25 times closer to its star than Earth does to the Sun. It probably migrated towards the star from a more distant orbit when friction with material in a disc around the star slowed it down, allowing the star's gravity to pull it closer.
Laughlin hopes to find more transiting planets to see how unusual this object is. The best data so far is on three extrasolar planets that transit bright stars, but all three are quite different. One is about a third larger in diameter than expected by theory, one is the predicted size, and this object is smaller and denser than expected.
That suggests planets lying very close to their stars - which are easiest for astronomers to detect - "are most likely to have suffered problems in the past", says Laughlin. "The fact you see oddballs all close to the star is telling us we're seeing the ruined fringes of the planetary distribution."
A paper on the newly discovered planet will be published in the Astrophysical Journal.
mmmm....computer....