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“Clear signs” of water on foreign solar system

July 11, 2007
Courtesy Caltech
and World Science staff

Re­search­ers say they have found the best ev­i­dence to date that plan­ets out­side our so­lar sys­tem have wa­ter.

“Wa­ter is the quin­tes­sence of life as we know it,” said Yuk Yung, a pro­fes­sor of plan­e­tary sci­ence at the Cal­i­for­nia In­sti­tute of Tech­nol­o­gy in Pas­a­de­na, Ca­lif. It’s “ex­cit­ing to find that it is as abun­dant in an­oth­er so­lar sys­tem as it is in ours.” Yung is co-au­thor of a pa­per on the find­ing, ap­pear­ing in this week’s is­sue of the re­search jour­nal Na­ture

Artist's con­cep­tion of HD 189733b. (Cred­it: Da­vid A. Aguilar [CfA])


As­tro­no­mers wrote that they found wa­ter’s chem­i­cal sig­na­ture in the at­mos­phere of a swel­t­er­ing plan­et called HD 189733b, sixty-three light-years away in the con­stella­t­ion Vul­pec­u­la. A light-year is the dis­tance light trav­els in a year.

The planet also re­cent­ly be­came the first to have its cli­mate mapped by hu­mans.

Re­search­ers had pre­dicted that plan­ets of its class, called “hot Jupiters,” would con­tain wa­ter va­por; re­cent ob­serva­t­ions had al­so sug­gested as much. The new re­search con­firmed this, us­ing the NASA Spitzer Space Tele­scope’s par­tic­u­larly keen abil­ity to study near­by stars and their plan­ets, sci­en­tists said.

They meas­ured changes in star­light as the plan­et slips in front of its star, fil­ter­ing star­light through its out­er at­mos­phere. The at­mos­phere was found to ab­sorb spe­cif­ic wave­lengths, or com­po­nents, of the light in a pat­tern char­ac­ter­is­tic of wa­ter con­tent.

“We’re thrilled to have iden­ti­fied clear signs of wa­ter on a plan­et that is tril­lions of miles away,” said Gio­van­na Ti­netti of the In­sti­tute d’As­tro­phy­sique de Par­is in France, lead au­thor of the Na­ture pa­per. “The dis­cov­ery of wa­ter is the key to the dis­cov­ery of al­ien life,” added co-au­thor Mao-Chang Liang of Cal­tech.

Al­though wa­ter is es­sen­tial to life as we know it, wet hot Ju­pi­ters probably don’t har­bor life. Temp­er­a­tures on HD 189733b are est­i­mated at a fiery 1,000 de­grees Kel­vin (1,340 de­grees Fahr­en­heit) on av­er­age. Ul­ti­mate­ly, as­tro­no­mers hope to use in­stru­ments like those on Spitzer to find wa­ter on rocky, hab­it­a­ble plan­ets like Earth.

“Find­ing wa­ter on this plan­et im­plies that oth­er plan­ets in the un­iverse, pos­sibly even rocky ones, could al­so have wa­ter,” said co-au­thor Sean Car­ey of the Spitzer Sci­ence Cen­ter at Cal­tech.


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Researchers say they have found the best evidence to date that planets outside our solar system have water. “Water is the quintessence of life as we know it,” said Yuk Yung, a professor of planetary science at the California Institute of Technology in Pasadena, Calif. It’s “exciting to find that it is as abundant in another solar system as it is in ours.” Yung is co-author of a paper on the finding, appearing in this week’s issue of the research journal Nature. Astronomers wrote that they found water’s chemical signature in the atmosphere of a hot planet called HD 189733b, located 63 light-years away in the constellation Vulpecula. A light-year is the distance light travels in a year. Researchers had predicted that planets of this class, called “hot Jupiters,” would contain water vapor; recent observations had also suggested as much. But the new research confirmed it, using the NASA Spitzer Space Telescope’s particularly keen ability to study nearby stars and their planets, scientists said. They measured changes in the starlight as the planet slips in front of the star, filtering starlight through its outer atmosphere. The atmosphere was found to absorb specific wavelengths, or components, of the starlight, in a pattern characteristic of water content. “We’re thrilled to have identified clear signs of water on a planet that is trillions of miles away,” said Giovanna Tinetti, a European Space Agency fellow at the Institute d’Astrophysique de Paris in France, and lead author of the Nature paper. “The discovery of water is the key to the discovery of alien life,” added coauthor Mao-Chang Liang of Caltech. Although water is an essential ingredient for life as we know it, wet hot Jupiters probably don’t harbor life. Previous measurements indicate that HD 189733b is a fiery 1,000 degrees Kelvin (1,340 degrees Fahrenheit) on average. Ultimately, astronomers hope to use instruments like those on Spitzer to find water on rocky, habitable planets like Earth. “Finding water on this planet implies that other planets in the universe, possibly even rocky ones, could also have water,” said co-author Sean Carey of the Spitzer Science Center, headquartered at Caltech. “I’m excited to tell my nephew and niece about the discovery.”