"Long before it's in the papers"
January 27, 2015

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Star found to have little planets over twice as old as our own

Jan. 27, 2015
Courtesy of Iowa State University
and World Science staff

As­tro­no­mers say they have found at least five smaller-than-Earth plan­ets or­bit­ing a star in a so­lar sys­tem over twice as old as our so­lar sys­tem.

Al­though the plan­ets are un­in­hab­it­a­ble due to heat, the find sug­gests life could have formed long be­fore our Earth formed, they add. The study shows that roughly “Earth-size plan­ets have formed through­out most of the uni­verse’s 13.8-bil­lion-year his­to­ry,” the as­tro­no­mers wrote in a re­port pub­lished to­day in The As­t­ro­phys­i­cal Jour­nal.

Artist's conception of Kep­ler-444. (Il­lus­tra­tion by Tia­go Cam­pan­te/Pe­ter De­vine)


As­tro­no­mers are in­ter­est­ed in find­ing plan­ets around Earth’s size or smaller, as these are con­sid­ered more likely to have a si­m­i­lar make­up to Earth than the easier-to-find gi­ant plan­ets.

The find­ing leaves “open the pos­si­bil­ity for the ex­ist­ence of an­cient life” in our gal­axy, the sci­en­tists wrote. They iden­ti­fied the star, called Kep­ler-444, us­ing da­ta from NASA’s now-defunct Kep­ler space­craft and es­ti­mat­ed its age as 11.2 bil­lion years.

The star is an es­ti­mat­ed 25 per­cent smaller than our Sun and is 117 light-years from Earth. A light-year is the dis­tance light trav­els in a year. The star is very bright and easily vis­i­ble with bin­oc­u­lars, said study co-author Steve Ka­waler of Io­wa State Uni­vers­ity.

Ac­cord­ing to the paper, its five known plan­ets have sizes be­tween those of Mer­cu­ry and Ve­nus, and are so close to their star that they go around it in few­er than 10 days. At that dis­tance, they’re all much hot­ter than Mer­cu­ry and aren’t hab­it­a­ble.

Kawaler and col­leagues as­sessed the size of the star by stu­dying sound waves with­in it. These af­fect its tem­per­a­ture, cre­at­ing pul­sat­ing changes in bright­ness that of­fer clues to its size, weight and age. Kep­ler takes pre­cise mea­sure­ments of those changes in bright­ness. These al­so re­veal wheth­er there are plan­ets, be­cause plan­ets cause ti­ny dips in a star’s bright­ness if they pass in front of it.

“This is one of the old­est sys­tems in the gal­axy,” Kawaler said of the new find­ing, not­ing that our Sun is 4.5 bil­lion years old. “Kep­ler-444 came from the first genera­t­ion of stars. This sys­tem tells us that plan­ets were form­ing around stars nearly 7 bil­lion years be­fore our own so­lar sys­tem.”

According to current theo­ries, plan­ets begin to form around the same time as their host star, out of a gas-and-dust cloud sur­round­ing the star.

“Plan­e­tary sys­tems around stars have been a com­mon fea­ture of our gal­axy for a long, long time,” Kawaler said.

The find­ing will help as­tro­no­mers learn even more about the his­to­ry of our Milky Way, he added. “We are now get­ting first glimpses of the va­ri­e­ty of ga­lac­tic en­vi­ron­ments con­du­cive to the forma­t­ion of these small worlds,” the as­tro­no­mers wrote. “As a re­sult, the path to­ward a more com­plete un­der­stand­ing of early plan­et forma­t­ion in the gal­axy starts un­fold­ing be­fore us.”


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Astronomers say they have found at least five smaller-than-Earth planets orbiting a star in a solar system over twice as old as our solar system. Although the planets are uninhabitable due to heat, the find suggests life could have formed long before our Earth formed, they add. The study shows that roughly “Earth-size planets have formed throughout most of the universe’s 13.8-billion-year history,” the astronomers wrote in a report published today in the Astrophysical Journal. Astronomers are interested in finding planets around Earth’s size or smaller, as these are considered more likely to have a similar makeup to Earth than the easier-to-find giant planets. The finding leaves “open the possibility for the existence of ancient life” in our galaxy, added the scientists. They identified the star, called Kepler-444, using data from NASA’s now-defunct Kepler spacecraft and estimated its age as 11.2 billion years. The star is an estimated 25 percent smaller than our Sun and is 117 light-years from Earth. A light-year is the distance light travels in a year. The star is very bright and easily visible with binoculars, said study co-author Steve Kawaler of Iowa State University. According to the study, the five known planets have sizes between those of Mercury and Venus, and are so close to their star that they go around it in fewer than 10 days. At that distance, they’re all much hotter than Mercury and aren’t habitable. Kawaler and colleagues assessed the size of the star by studying sound waves within it. These affect its temperature, creating pulsating changes in brightness that offer clues to its size, weight and age. Kepler takes precise measurements of those changes in brightness. These also reveal whether there are planets, because planets cause tiny dips in a star’s brightness if they pass in front of it. “This is one of the oldest systems in the galaxy,” Kawaler said of the new finding, noting that our Sun is 4.5 billion years old. “Kepler-444 came from the first generation of stars. This system tells us that planets were forming around stars nearly 7 billion years before our own solar system. “Planetary systems around stars have been a common feature of our galaxy for a long, long time.” The finding will help astronomers learn even more about the history of our Milky Way, he added. “We are now getting first glimpses of the variety of galactic environments conducive to the formation of these small worlds,” the astronomers wrote. “As a result, the path toward a more complete understanding of early planet formation in the galaxy starts unfolding before us.”