Across the Milky Way lies a violent world suffering through the first "superstorm" ever spotted on an alien planet.
Poisonous carbon monoxide gas is streaming at enormous speeds from the extremely hot day side to the cooler night side of the exoplanet, new observations show. This hot, gaseous Jupiter-like world is dubbed HD209458b, and lies about 150 light-years from Earth toward the constellation Pegasus.
"HD209458b is definitely not a place for the faint-hearted," said lead researcher Ignas Snellen of Leiden Observatory in the Netherlands. "By studying the poisonous carbon monoxide gas with great accuracy we found evidence for a super wind, blowing at a speed of 5,000 to 10,000 km per hour [3,100 to 6,200 mph]."
The new study, of a world first discovered in 1999, also enabled the astronomers to measure the planet's mass for the first time from calculations of its velocity. The researchers obtained new high-resolution views of the exoplanet using the European Southern Observatory's Very Large Telescope in Chile. [The Strangest Alien Planets]
HD209458b has about 60 percent the mass of Jupiter, yet orbits its star only one-twentieth the distance between the sun and Earth, which are separated by about 93 million miles (150 million km). These close quarters give the planet surface temperatures around 1,830 degrees Fahrenheit (1,000 degrees Celsius) on the hot side.
The researchers think radiation from the star is driving the strong winds and storms.
The tiny orbit also keeps one side of the world permanently facing its star – and thus very hot – while the dark side perpetually faces outward and is frigid.
"On Earth, big temperature differences inevitably lead to fierce winds, and as our new measurements reveal, the situation is no different on HD209458b," said co-researcher Simon Albrecht of MIT.
To learn about HD209458b, the astronomers observed it as it passed in front of its host star – a process that recurs every 3.5 days and is known as a transit. When this happens, the planet blocks most of the star's light, though a small fraction filters through the planet's atmosphere, which leaves an imprint on the light.
The researchers analyzed the faint fingerprints left by carbon monoxide to determine how fast the gas was moving on the surface of the planet. They could do this thanks to a phenomenon called the Doppler effect, which describes how light or sound waves will shift in frequency when their source moves.
The changes in Doppler shift over time also allowed the astronomers to calculate the velocity of the exoplanet as it moves around its star, which in turn enabled them to deduce its mass.
"In general, the mass of an exoplanet is determined by measuring the wobble of the star and assuming a mass for the star, according to theory," said co-researcher Ernst de Mooij. "Here, we have been able to measure the motion of the planet as well, and thus determine both the mass of the star and of the planet."
Previous studies of this planet also detected the basic molecules required for life in its atmosphere. The chemicals, including water, methane and carbon dioxide, are promising signs in the hunt for life beyond Earth, though no evidence has yet been found for extraterrestrials on HD209458b or anywhere in the universe.
The new observations provided more detail on the presence of carbon on the world.
"It seems that H209458b is actually as carbon-rich as Jupiter and Saturn," Snellen said. "This could indicate that it was formed in the same way. In the future, astronomers may be able to use this type of observation to study the atmospheres of Earth-like planets, to determine whether life also exists elsewhere in the Universe."
The findings are detailed in the June 24 issue of the journal Nature.
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