First Earth-sized planet in star’s “habitable zone” found

As­tro­no­mers said 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. But do not dream yet of living in the planet designated as Kepler-186F: 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.”

.Written by SETI Institute and World Science Staff