Jul 10, 2010

“Superstorm” detected on planet outside our system

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.

Artist's con­cept of plan­et HD209458b, with its host star in the back­ground. (Courtesy NA­SA)

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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