Astronomers have for the first time measured a “superstorm” in the atmosphere of a planet outside our solar system, according to a report.
Scientists say the planet, dubbed HD209458b, is similar to Jupiter in our system, but much hotter.
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Artist's concept of planet HD209458b, with its host star in the background. (Courtesy NASA)
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Carbon monoxide gas is continuously streaming at enormous speed from the planet’s scorching day side toward the cooler, night side, astronomers said. Their observations also allow another exciting “first,” they added: measuring the orbital speed of the planet itself. That provides a direct determination of its mass, the total amount of material that makes it up.
The findings are published this week in the research 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 5,000 to 10,000 km (3,000 to 6,000 miles) per hour‚” said Ignas Snellen of Leiden Observatory in The Netherlands, who led the group of astronomers.
The planet, with about 60 percent Jupiter’s mass, orbits a sun-like star located 150 light-years from Earth in the direction of the constellation Pegasus (the Winged Horse), researchers said. A light-year is the distance light travels in a year.
Circling the star at a distance of only one twentieth the distance between Sun and Earth, the planet’s hot side has a surface temperature estimated at a scalding 1,000 degrees Celsius. But as the planet always has its same side facing its star, one side is very hot; 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,” said team member Simon Albrecht of the Massachusetts Institute of Technology.
Every 3.5 days the planet moves in front of its host star from our point of view. It then blocks a bit of the starlight for three hours. This is the way the planet was originally detected.
During such events, a tiny fraction of the starlight filters through the planet’s atmosphere, which leaves an imprint on the star light. Snellen’s group analyzed this faint signature using European Southern Observatory’s Very Large Telescope and an attached spectrograph, or light analysis instrument.
Its “high precision allows us to measure the velocity of the carbon monoxide gas for the first time,” said another team member, Remco de Kok of the Netherlands Institute for Space Research. This measurement was based on the Doppler effect, in which characteristic dark lines that carbon monoxide leaves on the light’s spectrum are slightly shifted while the gas moves.
The astronomers said they achieved several other firsts. They directly measured the velocity of the planet as it orbits its home star. In general, the mass of a planet outside the solar system is determined by measuring the wobble of the star under the planet's influence, “and assuming a mass for the star, according to theory,” said co-author Ernst de Mooij of Leiden Observatory. “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.”
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,” said 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.”
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