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“Earth-like,” possibly habitable planets identified

April 19, 2013
Courtesy of the University of Notre Dame
and World Science staff

Re­search­ers say they have iden­ti­fied the first fairly Earth-sized plan­ets in a Sun-like star’s “hab­it­able zone.”

Im­ages of the star tak­en by as­t­ro­phys­i­cist Jus­tin Crepp of the Uni­vers­ity of Notre Dame in In­di­ana con­firm that five plan­ets or­bit the star Kep­ler 62, as­t­ro­phys­i­cists said. Two of them are cal­cu­lat­ed to lie in the hab­it­a­ble zone—the re­gion at suit­a­ble dis­tances from the star for liq­uid wa­ter to per­sist. The find­ings are pub­lished in the re­search jour­nal Sci­ence this week.

This artist's con­cep­tion de­picts Kepler-62e, a super-Earth-size plan­et in the hab­it­a­ble zone of a star smaller and cool­er than the sun, lo­cat­ed about 1,200 light-years from Earth in the con­stel­la­tion Ly­ra. This world is be­lieved to or­bits its host star eve­ry 122 days and is rough­ly 60 per­cent larg­er than Earth. Sci­en­tists say it could be a wa­ter­world or have a sol­id sur­face, but that either way its dis­cov­ery sig­nals an­oth­er step clos­er to find­ing a place a bit like Earth. (Im­age cour­te­sy NA­SA/Ames/JPL-Caltech.)


The hab­it­a­ble-zone plan­ets are 40 per­cent and 60 per­cent wid­er than Earth, re­spec­tive­ly, the sci­en­tists said.

The find­ing has been “val­i­dated with high sta­tis­ti­cal con­fi­dence,” the pa­per as­serts. The two worlds, dubbed Kep­ler-62 e and f, are the out­er­most of the five de­tected plan­ets and are es­ti­mat­ed to get about as much light and oth­er radia­t­ion from their star as Ve­nus and Mars get from the Sun. 

Their size sug­gests that they’re ei­ther rocky, like Earth, or made mostly of ice, the re­search­ers said. A plan­et dis­cov­ered more than a year ago in the hab­it­a­ble zone of anoth­er Sun-like star, Kep­ler-22, is 2.4 times as wide as Earth, leav­ing re­search­ers less sure of its make­up.

Based on their width and the time they take to cir­cle the star, “these are the most si­m­i­lar ob­jects to Earth that we have found yet,” said Crepp. The da­ta come from NASA’s Kep­ler mis­sion, launched in 2009 to iden­ti­fy plan­ets around oth­er suns. The proj­ect has so far re­sulted in sev­er­al doz­en of some 3,000 “Kep­ler Ob­jects of In­ter­est” hav­ing been stud­ied in de­tail.

Re­search­ers use fluctua­t­ions in a star’s bright­ness to iden­ti­fy po­ten­tial plan­ets reg­u­larly pass­ing in front of the star as they or­bit. Crepp uses large ground-based tele­scopes to im­age the star and an­a­lyzes the sys­tem to make sure oth­er events—such as near­by eclips­ing com­pan­ion stars—aren’t caus­ing the ob­served ef­fect. Crepp no­ticed a faint dot near Kep­ler-62 a year ago, lead­ing to months of de­tailed study to con­firm the plan­et in­ter­preta­t­ion.

“What really helped is that this star has five plan­ets,” he said. “You can mim­ic one plan­et with anoth­er event, but when you have five of them and they’re all per­i­od­ic, that helps to put the nail in the cof­fin. It’s hard to make that kind of sig­na­ture with an­y­thing else that you can dream up.”


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Researchers say they have identified the first Earth-sized planets in a Sun-like star’s “habitable zone.” Images of the star taken by astrophysicist Justin Crepp of the University of Notre Dame in Indiana confirm that five planets orbit the star Kepler 62, astrophysicists said. Two of them are calculated to lie in the habitable zone—the region at suitable distances from the star for liquid water to persist. The findings are published in the research journal Science this week. The habitable-zone planets are 40% and 60% wider than Earth, respectively, the scientists said. The finding has been “validated with high statistical confidence,” the paper asserts. The two worlds, dubbed Kepler-62 e and f, are the outermost of the five detected planets and are estimated to get about as much light and other radiation from their star as Venus and Mars get from the Sun. Their size suggests that they’re either rocky, like Earth, or made mostly of ice, the researchers said. A planet discovered more than a year ago in the habitable zone of another Sun-like star, Kepler-22, is 2.4 times as wide as Earth, leaving researchers less sure of its makeup. Based on their width and the time they take to circle the star, “these are the most similar objects to Earth that we have found yet,” said Crepp. The data come from NASA’s Kepler mission, launched in 2009 to identify planets around other suns. The project has so far resulted in several dozen of some 3,000 “Kepler Objects of Interest” having been studied in detail. Researchers use fluctuations in a star’s brightness to identify potential planets regularly passing in front of the star as they orbit. Crepp uses large ground-based telescopes to image the star and analyzes the system to make sure other events—such as nearby eclipsing companion stars—aren’t causing the observed effect. Crepp noticed a faint dot near Kepler-62 a year ago, leading to months of detailed study to confirm the planet interpretation. “What really helped is that this star has five planets,” he said. “You can mimic one planet with another event, but when you have five of them and they’re all periodic, that helps to put the nail in the coffin. It’s hard to make that kind of signature with anything else that you can dream up.”