The ex­ist­ence of a world with a dou­ble sun­set, as por­trayed in the film Star Wars more than 30 years ago, is now a known fact, as­tro­no­mers say.

Sci­en­tists an­nounced Sept. 15 that NASA’s Kep­ler mis­sion has made the first clear de­tec­tion of a “cir­cumbi­na­ry” plan­et, a plan­et or­bit­ing two stars. The body is 200 light-years from Earth; a light-year is the dis­tance light trav­els in a year.

Un­like Star Wars’ Tatooine, the plan­et is cold, gas­e­ous and not thought to har­bor life, but its dis­cov­ery demon­strates the di­vers­ity of plan­ets in our gal­axy, ac­cord­ing to re­search­ers. Pre­vi­ous re­search had hinted at the ex­ist­ence of cir­cum­bi­nary plan­ets, but clear con­firma­t­ion proved elu­sive. A 2005 study re­port­ed a planet in a three-star sys­tem, but it was ap­par­ently only or­bit­ing one of those stars.

Kep­ler de­tected the plan­et, known as Kep­ler-16b, by ob­serv­ing tran­sits, events in which the bright­ness of a par­ent star dims from the plan­et cross­ing in front of it. “This dis­cov­ery con­firms a new class of plan­etary sys­tems that could har­bor life,” Kep­ler prin­ci­pal in­ves­ti­ga­tor Wil­liam Borucki said. “Given that most stars in our gal­axy are part of a bi­na­ry sys­tem, this means the op­por­tun­i­ties for life are much broader than if plan­ets form only around sin­gle stars. This mile­stone dis­cov­ery con­firms a the­o­ry that sci­en­tists have had for dec­ades but could not prove un­til now.”

A re­search team led by Lau­rance Doyle of the SETI In­sti­tute in Moun­tain View, Calif., used da­ta from the Kep­ler space tel­e­scope, which meas­ures dips in the bright­ness of more than 150,000 stars, to search for tran­sit­ing plan­ets. Kep­ler is the first NASA mis­sion ca­pa­ble of find­ing Earth-size plan­ets in or near the “hab­it­able zone,” the re­gion in a plan­etary sys­tem where liq­uid wa­ter can ex­ist on the sur­face of the or­bit­ing plan­et.

Sci­en­tists de­tected the new plan­et in the Kep­ler-16 sys­tem, a pair of or­bit­ing stars that eclipse each oth­er from our van­tage point on Earth. When the smaller star par­tially blocks the larg­er star, a pri­ma­ry eclipse oc­curs, and a sec­ond­ary eclipse oc­curs when the smaller star is oc­culted, or com­pletely blocked, by the larg­er star.

As­tro­no­mers fur­ther ob­served that the bright­ness of the sys­tem dipped even when the stars were not eclips­ing one anoth­er, hint­ing at a third body. The ad­di­tion­al dim­ming in bright­ness events, called the ter­tiary and qua­ter­nary eclipses, reap­peared at ir­reg­u­lar in­ter­vals of time, in­di­cat­ing the stars were in dif­fer­ent po­si­tions in their or­bit each time the third body passed. This showed the third body was cir­cling, not just one, but both stars, in a wide cir­cumbi­nary or­bit.

The gravita­t­ional tug on the stars, meas­ured by changes in their eclipse times, was a good in­di­ca­tor of the mass of the third body. Only a very slight gravita­t­ional pull was de­tected, one that only could be caused by a small mass. The find­ings are de­scribed in a new study pub­lished Sept. 16 in the jour­nal Sci­ence.

“Most of what we know about the sizes of stars comes from such eclips­ing bi­na­ry sys­tems, and most of what we know about the size of plan­ets comes from tran­sits,” said Doyle, who al­so is the lead au­thor of the study and a Kep­ler par­ti­ci­pat­ing sci­ent­ist. “Kep­ler-16 com­bines the best of both worlds, with stel­lar eclipses and plan­etary tran­sits in one sys­tem.”

Kep­ler-16b is an in­hos­pi­ta­b, cold world about the size of Sat­urn and thought to be made up of about half rock and half gas, as­tro­no­mers said. The par­ent stars are smaller than our Sun. One is 69 per­cent the mass of the Sun and the oth­er only 20 per­cent. Kep­ler-16b or­bits around both stars every 229 days, si­m­i­lar to Venus’ 225-day or­bit, but lies out­side the sys­tem’s hab­it­a­ble zone, where liq­uid wa­ter could ex­ist on the sur­face, be­cause the stars are cool­er than our Sun.

“Work­ing in film, we of­ten are tasked with cre­at­ing some­thing nev­er be­fore seen,” said vis­u­al ef­fects su­per­vi­sor John Knoll of In­dus­t­ri­al Light & Mag­ic, a di­vi­sion of Lu­cas­film Ltd., in San Fran­cis­co. “How­ever, more of­ten than not, sci­en­tif­ic dis­cov­er­ies prove to be more spec­tac­u­lar than an­y­thing we dare im­ag­ine. There is no doubt these dis­cov­er­ies in­flu­ence and in­spire sto­ry­tellers. Their very ex­ist­ence serves as cause to dream big­ger and open our minds to new pos­si­bil­i­ties be­yond what we think we ‘know.’”

Story taken from World Science
http://www.world-science.net/othernews/110915_circumbinary

It has to be called Tatooine!