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First map of planet outside our system

May 9, 2007
Special to World Science  

As­tro­no­mers are de­vis­ing ways to make maps of the dis­tant plan­ets that are being found out­side our so­lar sys­tem. Re­search­ers an­nounced Wednes­day that they had cre­at­ed the first such map.

The hope is to one day chart Earth-like worlds that may have oceans, con­ti­nents and life. For now, the plan­et just mapped—and on­ly rough­ly—is a gas gi­ant with no sol­id sur­face, so the map shows cloud-top fea­tures on­ly. It in­cludes a bright hot spot off­set from “high noon,” where heat­ing is great­est.

A map of the "hot Jupi­ter" plan­et HD 189733b. The map shows a "hot spot" off­set from the sub­stel­lar point (high noon) by about 30 de­grees. (Cred­it: NA­SA/JPL-Cal­tech/Hea­ther Knut­son (CfA))


“We are get­ting our first good look at a com­plete­ly al­ien world,” said Heath­er Knut­son, a grad­u­ate stu­dent at Har­vard Uni­ver­si­ty in Cam­b­ridge, Mass. and lead au­thor of a pa­pe­r on the map in the May 10 is­sue of the re­search jour­nal Na­ture.

“We felt a lit­tle like Gal­i­le­o must have felt when he first glimpsed Ju­pi­ter” through his tele­scope, she added.

The team ex­am­ined the plan­et, known as HD 189733b, us­ing the In­fra­red Ar­ray Cam­era on NA­SA’s Spitzer Space Tel­e­scope. The cam­era records in­fra­red light emis­sions on­ly, an ad­van­tage be­cause the great bright­ness dif­fer­ence be­tween star and plan­et is re­duced in this form of light. That makes it eas­i­er to tease out the plan­et’s sig­nal.

Spitzer can on­ly map large, hot worlds, too hot for liq­uid wa­ter or life. But the James Webb Space Tel­e­scope sched­uled for launch in 2013 may be able to map Earth-like worlds us­ing the tech­nique Knut­son and her col­leagues pi­o­neered, the group said.

By meas­ur­ing changes as the plan­et turned, the team cre­at­ed a sim­ple lon­gi­tu­di­nal map. That is, they meas­ured the plan­et’s bright­ness in a se­ries of pole-to-pole strips across the vis­i­ble cloud-tops, then com­bined the re­sults. “We can see the changes in bright­ness” as the ob­ject spins, Knut­son ex­plained.

The map re­vealed one “hot spot” about twice as big as Ju­pi­ter’s Great Red Spot and much hot­ter, she added, a scorch­ing 1,700 de­grees Fahr­en­heit. Cu­ri­ous­ly, re­search­ers found the plan­et’s hot­test point is­n’t the one di­rect­ly be­low its sun—where it’s “high noon” on the plan­et—but rath­er is off­set by about 30 de­grees. They spec­u­late that the shift is due to winds re­dis­trib­ut­ing heat.

Artist's con­cep­tion of HD 189733b, which some have dubbed the "Bulls-eye" plan­et be­cause of the bright "hot spot" shown here. (Cred­it: Da­vid A. Aguilar [CfA])


“This plan­et has pow­er­ful je­t streams. While Earth’s je­t stream b­lows at around 200 miles per hour, the je­t stream on HD 189733b may b­low as fast as 6,000 miles per hour,” said co-au­thor Da­vid Char­bon­neau of the Har­vard-Smithsonian Cen­ter for As­t­ro­phys­ics in Cam­bridge, Mass.

The strong, hot winds may al­so help keep the plan­et’s night side warm, re­search­ers added. With­out these, that side would freeze while the side fac­ing the star would broil; but “ev­ery night is hot on this world,” which is slight­ly larg­er than Ju­pi­ter, Knut­son said. 

The planet is tidally locked, mean­ing one side always faces the star and the other is al­ways dark, just as the moon is ti­dally locked to Earth. The as­tro­no­mers meas­ured a max­i­mum tempe­rature dif­fer­ence of about 500 de­grees Fahr­en­heit, with the night side’s cold­est re­gions re­main­ing a balmy 1200 de­grees.

An­oth­er as­tron­o­mer has pro­posed a meth­od for map­ping Earth-like plan­ets by de­tect­ing the “glint” from their oceans. The idea is that as the world spins, this glint changes or dis­ap­pears, giv­ing ob­servers a rough idea of the width of oceans and in­ter­ven­ing con­ti­nents. 

A var­i­ant of that tech­nique might be used to chart the sup­pos­ed­ly Earth-like plan­et Gliese 581c, whose dis­cov­ery was an­nounced last month, said Pe­ter R. Mc­Cul­lough of the Space Tel­e­scope Sci­ence In­sti­tute in Bal­ti­more. He has sub­mit­ted the map­ping idea in a pa­pe­r to The As­t­ro­phys­i­cal Jour­nal. But he added that the meth­od as cur­rent­ly en­vi­sioned would have dif­fi­cul­ty with Gliese 581c be­cause it’s very close to its par­ent star so its light is hard to dis­tin­guish. Var­i­ous re­search pro­jects un­der­way could over­come that prob­lem, he added.

The tech­nique is “the next step we sci­en­tists need to make to go from ‘could have wa­ter on its sur­face’ to ‘wa­ter IS on its sur­face,’ he wrote in an e­mail. Gliese 581c “is just the first of many such sys­tems that will be found and oth­ers may be more suita­ble.”


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Astronomers are devising ways to make maps of the distant planets that lie outside our solar system, and announced Wednesday that they had created the first such map. The hope is to one day chart Earth-like worlds that may have oceans, continents and life. For now, the planet just mapped—and only roughly—is a gas giant with no solid surface, so the map shows cloud-top features only. It includes a bright hot spot offset from “high noon,” where heating is greatest. “We are getting our first good look at a completely alien world,” said Heather Knutson, a graduate student at Harvard University and lead author of a paper about the research appearing in the May 10 issue of the research journal Nature. “We felt a little like Galileo must have felt when he first glimpsed Jupiter through the eyepiece of his telescope,” she added. The team examined the planet, known as HD 189733b, using the Infrared Array Camera on NASA’s Spitzer Space Telescope. The camera records infrared light emissions only, an advantage because the great brightness difference between star and planet is reduced in this form of light. That makes it easier to tease out the planet’s signal. Spitzer can only map large, hot worlds, too hot for liquid water or life. However, the upcoming James Webb Space Telescope scheduled for launch in 2013 may be able to map Earth-like worlds using the technique Knutson and her colleagues pioneered, the group said. By measuring changes as the planet rotated, the team created a simple longitudinal map. That is, they measured the planet’s brightness in a series of pole-to-pole strips across the planet’s visible cloud-tops, then combined the results. “We can see the changes in brightness” as the object spins, Knutson explained. The map revealed a single “hot spot” that is about twice as big as the Great Red Spot on Jupiter and much hotter, she added, a scorching 1700 degrees Fahrenheit. Curiously, researchers found the planet’s hottest point isn’t the one directly below its sun—where it’s “high noon” on the planet—but rather is offset by about 30 degrees. They speculate that the shift is due to winds redistributing heat. “This planet has powerful jet streams. While Earth’s jet stream blows at around 200 miles per hour, the jet stream on HD 189733b may blow as fast as 6,000 miles per hour,” said co author David Charbonneau of the Harvard-Smithsonian Center for Astro physics in Cambridge, Mass. The strong, hot winds may also help keep the planet’s night side warm, researchers added. Without these, that side would freeze while the side facing the star would broil; but “every night is hot on this world,” which is slightly larger than Jupiter, Knutson said. The astronomers measured a maximum temperature difference of about 500 degrees Fahrenheit, with the night side’s coldest regions remaining a balmy 1200 degrees F. Another astronomer has proposed a method for mapping Earth-like planets by detecting the “glint” from their oceans. The idea is that as the world spins, this glint changes, giving observers a rough idea of the approximate width of oceans and intervening continents. A variant of that technique might be used to chart the supposedly Earth-like planet Gliese 581c, whose discovery was announced last month, said Peter R. McCullough of the Space Telescope Science Institute in Baltimore. He submitted the mapping idea last October in a paper to The Astro physical Journal. But he added that the method as currently envisioned would have difficulty with the planet because it’s very close to its parent star and thus hard to distinguish. Various research projects underway could change that, he added. The technique “is exactly the next step we scientists need to make to go from ‘could have water on its surface’ to ‘water IS on its surface,’ he wrote in an email. Gliese 581C “is just the first of many such systems that will be found and others may be more suitable.”