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First Earth-sized planet in star’s "habitable zone"

First Earth-sized planet in star’s

In a long-awaited first, as­tro­no­mers say they have found an Earth-sized plan­et, out­side our own so­lar sys­tem, or­bit­ing a star at a dis­tance suit­a­ble to al­low liq­uid wa­ter on the plan­et's sur­face.
That means it could po­ten­tially host life-though no sig­nals have been de­tected from the body, des­ig­nat­ed Kep­ler-186f, as­tro­no­mers add. Kep­ler-186f is meas­ured to be so far away from us that even mov­ing at light speed, it would take al­most an es­ti­mat­ed five cen­turies to get there. Any radio or light signals reach­ing us from the plan­et would be that old also.

Still, “this is the first de­fin­i­tive Earth-sized plan­et found in the ‘hab­it­a­ble zone' around an­oth­er star,” said Elisa Quin­tana of the SETI In­sti­tute at NASA Ames Re­search Cen­ter in Moun­tain View, Ca­lif. She is the lead au­thor of a re­port on the find­ings pub­lished in the re­search jour­nal Sci­ence.

“Find­ing such plan­ets is a pri­ma­ry goal of the Kep­ler space tele­scope,” she added. “The star is a main-sequence M-dwarf, a very com­mon type. More than 70 per­cent of the hun­dreds of bil­lions of stars in our gal­axy are M-dwarfs.”

The finding will surely shape fu­ture in­ves­ti­ga­t­ions of exoplan­ets, or plan­ets out­side our own so­lar sys­tem, with pos­si­ble Earth-like sur­faces, sci­en­tists said. The body is the fifth and out­er­most world to be de­tected in the plan­etary sys­tem of a red dwarf star known as Kep­ler-186. The star lies ap­prox­i­mate­ly in the dir­ect­ion of the con­stell­ation Cyg­nus, the Swan, in the north­ern sky on the plane of the Mil­ky Way.

Of the nearly 1,800 con­firmed exoplan­ets found in the past two dec­ades, about 20 are thought to or­bit their host star in the hab­it­a­ble zone-a range of or­bital dis­tances at which sur­face wa­ter on a plan­et with an at­mos­phere would nei­ther freeze nor boil. But all of these are larg­er than Earth, so they might be gas­e­ous plan­ets, like the larg­er plan­ets of our own so­lar sys­tem. The au­thors es­ti­mate the new­found plan­et is less then 10 per­cent wider than Earth, based on a meas­ured dim­ming of star­light from Kep­ler-186 as the plan­et passes in front of it.

The­o­ret­i­cal mod­els sug­gest that plan­ets up to about 1.5 times as wide as Earth “are un­likely to be swathed in at­mos­pheres of hy­dro­gen and he­li­um, the fate that's be­fall­en the gas gi­ants of our own so­lar sys­tem,” ex­plained Thom­as Barc­lay, a staff sci­ent­ist for the Kep­ler mis­sion af­fil­i­at­ed with both NASA and the Bay Ar­ea En­vi­ron­men­tal Re­search In­sti­tute.

So “Kep­ler-186f is likely a rocky world, and in that sense si­m­i­lar to Ve­nus, Earth and Mars.”

Plan­ets or­bit­ing red dwarf stars were tra­di­tion­ally con­sid­ered not very hab­it­a­ble. This is be­cause they would have to cir­cle their stars quite closely to get warmth, but this would lead to “ti­dal lock­ing,” a situa­t­ion in which the same side of the plan­et al­ways faces the star. Then one side would pre­sumably get ex­tremely hot, the oth­er frig­idly cold.

Yet more re­cent mod­el­ing stud­ies sug­gest winds or ocean cur­rents could re­duce this prob­lem by evening out tem­per­a­ture varia­t­ions. Kep­ler-186f is al­so far enough away from its host star that it's probably not locked, the as­tro­no­mers said, and likely al­so not too vul­ner­a­ble to stel­lar flares, com­mon with dwarf stars.

As­tro­no­mers are look­ing for any sig­nals sug­gestive of life us­ing the SETI In­sti­tute's Al­len Tel­e­scope Ar­ray, which ob­serves Kep­ler can­di­date exo­plan­ets.

Ac­cord­ing to Quin­tana, at a dis­tance of 490 light-years away from us, Kep­ler-186f may be too dim for fol­low-up sur­veys to probe its at­mos­phere, even with next-genera­t­ion tele­scopes. A light-year is the dis­tance light trav­els in a year.

But “our re­search tells us that we should be able to find plan­ets around bright stars that will be ide­al tar­gets to ob­serve with James Web­b,” a NASA space-based tel­e­scope now un­der con­struc­tion, she said. That's ex­pected to be able to di­rectly im­age plan­ets around near­by dwarf stars, and break up their light to de­scribe their at­mos­pheres.



Source : http://www.world-science.net

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