by Staff Writers
Paris (AFP) June 23, 2010
A planet named after ancient Egypt's Lord of the Dead is a place where human beings would be simultaneously boiled, poisoned and ripped apart by superstorms, astronomers reported on Wednesday.
The distant world, orbiting a bright star in the constellation of Pegasus 150 light years from Earth, is known officially as HD 209458b, but has been nicknamed Osiris, the god of the Egyptian underworld.
The label is especially fitting, given insights into the planet's climate system reported in the science journal Nature.
Osiris races around its yellow, Sun-like star at a distance of around seven million kilometres (4.37 million miles) -- less than a twentieth of the distance between Earth and the Sun -- which means its "year" is just three and a half days.
On one side its surface is heated to a scorching 1,100 degrees Celsius (1,800 degrees Fahrenheit), although the other side is far cooler.
The planet's atmosphere is laced with poisonous carbon monoxide and prey to storm winds that blow from 5,000 to 10,000 kph (3,100-6,200 mph), says the paper.
"HD 209458b is definitely not a place for the faint-hearted," quipped Ignas Snellen of Leiden Observatory, the Netherlands, who led a team of astronomers in the probe of the planet.
Snellen's team observed Osiris for five hours last August, using the European Southern Observatory's Very Large Telescope (VLT) in the desert of Chile.
The mission was to get a snapshot of the planet's atmosphere, using the VLT's infrared spectrograph, as the far-off world swung between its host star and Earth.
For three precious hours, the planet's transit in front of its sun caused telltale changes in starlight received by the Earth-bound telescope. These tiny alterations were then transcribed as signatures of atmospheric physics and chemistry.
A total of 462 exoplanets -- worlds in solar systems other than our own -- have been logged since the first was detected in 1995. None, though, is even remotely similar to our own planet, which is rocky and has water existing in liquid form.
HD 209458b is one of the most-studied exoplanets. It has previously been measured at 60 percent the mass of Jupiter, the gas giant that is the biggest planet of our own star system.
But it is far hotter, given its searing proximity to its own sun.
The very precise measurements of carbon monoxide shows that the gas flows at extraordinary speed from the hot side to the cool side of the planet.
"On Earth, big temperature differences inevitably lead to fierce winds and, as our new measurements reveal, the situation is no different on HD 209458b," said team member Simon Albrecht.
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