ESO Science Release (eso1026) | 23 June 2010
Supersonic Winds Rip Alien WorldAstronomers have measured a superstorm for the first time in the atmosphere of an exoplanet, the well-studied “hot Jupiter” HD209458b. The very high-precision observations of carbon monoxide gas show that it is streaming at enormous speed from the extremely hot day side to the cooler night side of the planet. The observations also allow another exciting “first” — measuring the orbital speed of the exoplanet itself, providing a direct determination of its mass.
The results appear this week in the journal Nature.
“HD209458b is definitely not a place for the faint-hearted. By studying the poisonous carbon monoxide gas with great accuracy we found evidence for a super wind, blowing at a speed of 5000 to 10 000 km per hour‚” says Ignas Snellen, who led the team of astronomers.
HD209458b is an exoplanet of about 60% the mass of Jupiter orbiting a solar-like star located 150 light-years from Earth towards the constellation of Pegasus (the Winged Horse). Circling at a distance of only one twentieth the Sun–Earth distance, the planet is heated intensely by its parent star, and has a surface temperature of about 1000 degrees Celsius on the hot side. But as the planet always has the same side to its star, one side is very hot, while the other is much cooler. “On Earth, big temperature differences inevitably lead to fierce winds, and as our new measurements reveal, the situation is no different on HD209458b,” says team member Simon Albrecht.
HD209458b was the first exoplanet to be found transiting: every 3.5 days the planet moves in front of its host star, blocking a small portion of the starlight during a three-hour period. During such an event a tiny fraction of the starlight filters through the planet’s atmosphere, leaving an imprint. A team of astronomers from the Leiden University, the Netherlands Institute for Space Research (SRON), and MIT in the United States, have used ESO’s Very Large Telescope and its powerful CRIRES spectrograph to detect and analyse these faint fingerprints, observing the planet for about five hours, as it passed in front of its star. “CRIRES is the only instrument in the world that can deliver spectra that are sharp enough to determine the position of the carbon monoxide lines at a precision of 1 part in 100 000,” says another team member Remco de Kok. “This high precision allows us to measure the velocity of the carbon monoxide gas for the first time using the Doppler effect.”
The astronomers achieved several other firsts. They directly measured the velocity of the exoplanet as it orbits its home star. “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. 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,” says co-author Ernst de Mooij.
Also for the first time, the astronomers measured how much carbon is present in the atmosphere of this planet. “It seems that H209458b is actually as carbon-rich as Jupiter and Saturn. This could indicate that it was formed in the same way,” says Snellen. “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.”
ScienceNOW | ScienceShot | 23 June 2010
An exoplanet's massHurricane Katrina would be regarded as a gentle breeze on HD 209458b. The giant planet, located about 150 light-years away in the constellation Pegasus, is a hot Jupiter—nearly as big as our own gas giant, but orbiting very close to its parent star. Like Mercury and our moon, the planet is tidally locked, meaning it always shows the same face to its sun. As a result, HD 209458b's dayside surface temperature never dips below 1000˚C, while its night side temperatures are hundreds of degrees cooler. Such a large temperature gradient generates eye-popping wind speeds. How fast? By carefully analyzing the spectra of starlight streaming through its atmosphere when the planet passes in front of its star, researchers report online today in Nature that HD 209458b generates winds of toxic carbon monoxide reaching 7000 kilometers per hour. That's twice as fast as any aircraft has ever flown—not that anyone would want to fly across this world.
- Nature | Vol 465 (24 June 2010) | Editor's Summary
Astronomy: Exoplanet caught speedingMost of the known exoplanets were discovered using the radial velocity method, measuring the 'wobble' induced in the host stars by their orbiting companions. If the orbital velocity of the planet can also be determined, it becomes possible to calculate the masses of both the star and its exoplanet without the need for further assumptions or model dependencies. That has now been achieved for the well-studied 'hot Jupiter' HD 209458b, based on spectroscopic measurements of the changing Doppler shift of molecular absorption lines of carbon monoxide, observed as the planet passed between its host star and the Earth. The masses of the star and planet are 1.00±0.22 solar masses and 0.64±0.09 jovian masses respectively. Also revealed — as blueshift of the carbon monoxide signal with respect to host star velocity — a strong wind flowing at high altitude from the irradiated dayside to the non-irradiated nightside of the planet.
- Nature | Vol 465 (24 June 2010) | DOI: 10.1038/4651017a
The orbital motion, absolute mass and high-altitude winds of exoplanet HD 209458bThe masses of exoplanets have so far been inferred from the tiny gravitational pull they exert on the host stars. It is now possible to measure them from shifts in spectral lines arising from the planets' atmospheres.
- Nature, Vol 465 (24 June 2010), DOI: 10.1038/nature09111
Space.com | 23 June 2010
Extra-Stormy Weather: Exoplanet Atmosphere Roils with Superspeed WindsAcross the Milky Way lies a violent world with 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.
Scientific American | 23 June 2010
A new look at a well-observed extrasolar planet reveals winds whipping through its upper atmosphere at 7,000 kilometers per hour
A long-studied planet orbiting a star 150 light-years away has been given a new look, thanks to a novel method of studying extrasolar planets from Earth.
The planet, which goes by the unmemorable name of HD 209458 b, became in 1999 the first world spotted as it passed in front of its host star, an event known as a transit that reveals the fortuitously aligned planet's presence through the slight dimming of the star. Even though astronomers cannot see a transiting planet directly—its presence is inferred by shifts in the host star's apparent brightness and confirmed by other effects—they can track the spectrum of starlight through the object's orbit to isolate contributions from the planet.
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