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"Long before it's in the papers"
February 20, 2013

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Tiny planet found

Feb. 20, 2013
Courtesy of Iowa State University
and World Science staff

As­tro­no­mers have made what they say are the first ob­serva­t­ions of a plan­et out­side our so­lar sys­tem smaller than Mer­cu­ry, the small­est plan­et or­bit­ing our sun.

Iden­ti­fied by studying nearly three years of high-pre­ci­sion da­ta from NASA’s Kep­ler space­craft, the plan­et is es­ti­mat­ed as be­ing about the size of the Earth’s moon. It is one of three plan­ets or­bit­ing a star des­ig­nat­ed Kep­ler-37 in the Cygnus-Lyra re­gion of the Milky Way.

The Kep­ler craft, shown in space in this artist's con­cep­tion,  finds plan­ets be­yond our so­lar sys­tem by de­tect­ing changes in star bright­ness when a plan­et passes in front of a star. (Im­age by NA­SA/Kep­ler Mis­sion/Wendy Sten­zel)
“The de­tec­tion of such a small plan­et shows for the first time that stel­lar sys­tems host plan­ets much smaller as well as much larg­er than an­y­thing we see in our own So­lar Sys­tem,”  the as­tron­o­mers wrote in a sum­mary of their find­ings. 

“Ow­ing to its ex­tremely small size, si­m­i­lar to that of the Earth’s moon,” and ra­di­ation-blasted sur­face, they added, it’s “very likely a rocky plan­et with no at­mos­phere or wa­ter, si­m­i­lar to Mer­cu­ry.”

The finding shows “we have a prov­en tech­nol­o­gy for find­ing small plan­ets around oth­er stars,” said study col­la­bo­ra­tor Steve Ka­wa­ler, an Io­wa State Uni­vers­ity as­tron­o­mer.

The find­ings were pub­lished on­line on Feb. 20 by the jour­nal Na­ture.

The re­search­ers first stud­ied the os­cilla­t­ions of the host star to learn its size, Ka­wa­ler ex­plained. “That’s bas­ic­ally lis­ten­ing to the star by meas­ur­ing sound waves,” he said. “The big­ger the star, the low­er the fre­quen­cy, or ‘pitch’ of its song.” The team de­ter­mined Kep­ler-37 weighs about four-fifths of our sun, the light­est star as­tron­o­mers have been able to meas­ure us­ing os­cilla­t­ion da­ta for an or­di­nary star.

This information al­lowed the main re­search team to bet­ter meas­ure the three plan­ets or­bit­ing Kep­ler-37, in­clud­ing the ti­ny one, Kep­ler-37b, the sci­en­tists said.

Kawaler said the dis­cov­ery is ex­cit­ing be­cause of what it says about the Kep­ler mis­sion’s ca­pa­bil­i­ties to dis­cov­er new plan­etary sys­tems. Kep­ler launched March 6, 2009, from Flori­da’s Cape Ca­nav­er­al Air Force Sta­t­ion. The space­craft cir­cles the sun car­ry­ing a pho­tom­e­ter, or light me­ter, to check changes in the bright­ness of thou­sands of stars. It de­tects ti­ny varia­t­ions in bright­ness to in­di­cate plan­ets pass­ing in front of the star. As­tro­no­mers with the Kep­ler team are look­ing for earth-like, habita­ble plan­ets.

The lat­est find­ing could have im­plica­t­ions for some wid­er dis­cov­eries: “while a sam­ple of only one plan­et is too small to use for de­ter­mina­t­ion of oc­cur­rence rates,” the as­tron­o­mers wrote, “it does lend weight” to the idea that small plan­ets are far more com­mon than large ones.

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Astronomers have used NASA’s Kepler spacecraft to make the first observations of a planet outside our solar system that’s smaller than Mercury, the smallest planet orbiting our sun. Identified by compiling nearly three years of high precision data from Kepler, the planet is estimated as being about the size of the Earth’s moon. It is one of three planets orbiting a star designated Kepler-37 in the Cygnus-Lyra region of the Milky Way. The findings were published online on Feb. 20 by the journal Nature. Researchers studied the oscillations of Kepler-37 to determine its size, explained study collaborator Steve Kawaler, an Iowa State University astronomer. “That’s basically listening to the star by measuring sound waves,” he said. “The bigger the star, the lower the frequency, or ‘pitch’ of its song.” The team determined Kepler-37 weighs about four-fifths of our sun, the lowest weight star astronomers have been able to measure using oscillation data for an ordinary star. Thoe measurements also allowed the main research team to better measure the three planets orbiting Kepler-37, including tiny Kepler-37b, the scientists said. “Owing to its extremely small size, similar to that of the Earth’s moon, and highly irradiated surface, Kepler-37b is very likely a rocky planet with no atmosphere or water, similar to Mercury,” the astronomers wrote in a summary of their findings. “The detection of such a small planet shows for the first time that stellar systems host planets much smaller as well as much larger than anything we see in our own Solar System.” Kawaler said the discovery is exciting because of what it said about the Kepler mission’s capabilities to discover new planetary systems. Kepler launched March 6, 2009, from Florida’s Cape Canaveral Air Force Station. The spacecraft circles the sun carrying a photometer, or light meter, to check changes in the brightness of thousands of stars. Its main job is to detect tiny variations in brightness to indicate planets passing in front of the star. Astronomers with the Kepler team are looking for earth-like, habitable planets. The latest finding shows “we have a proven technology for finding small planets around other stars,” Kawaler said. That could have implications for some wider discoveries: “While a sample of only one planet is too small to use for determination of occurrence rates,” the astronomers wrote in the Nature paper, “it does lend weight” to the idea that small planets are far more common than large ones.