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That habitable planet might not be so far off

March 10, 2008
Courtesy U. California, Santa Cruz
and World Science staff

An Earth-like, hab­it­a­ble plan­et may be in our stel­lar neigh­bor­hood, and could be found with a ded­i­cat­ed tel­e­scope, new com­put­er sim­ula­t­ions sug­gest.

Astro­nom­ers have long been looking for potentially ha­bi­table planets, and one team fi­nal­ly re­ported a can­di­date pla­ne­tary sys­tem last year. But no place where re­search­ers have pinned their hopes is nearly as close where the new study points.

The Al­pha Cen­tau­ri tri­ple stel­lar sys­tem is our clos­est neigh­bour in space. It lies 4.36 light-years away in the di­rec­tion of the south­ern con­stel­la­tion Cen­tau­rus. In the above pho­to, the two brighter stars of the sys­tem ap­pear as merged to­geth­er due to their lu­mi­nos­i­ty and prox­im­i­ty. The small ar­row at low­er right in­di­cates the lo­ca­tion of the third, dim star, Prox­i­ma Cen­tau­ri. (Cred­it: 1-Meter Schmidt Tel­e­scope, ESO)


The near­est stars to our Sun are in the three-star sys­tem called Al­pha Cen­tau­ri—a pop­u­lar trav­el des­tina­t­ion in sci­ence fic­tion, though it’s un­likely hu­mans could get there an­y­time soon.

Us­ing sim­ula­t­ions based on cur­rent plan­et-forma­t­ion the­o­ries, re­search­ers con­clud­ed that Earth-like plan­ets should have formed around one mem­ber of this sys­tem, the star Al­pha Cen­tau­ri B. 

One of these worlds, they added, could well be or­bit­ing in the star’s “hab­it­a­ble zone,” a re­gion suitably warm for liq­uid wa­ter to ex­ist on a plan­et sur­face.

“If they ex­ist, we can ob­serve them,” said Ja­vie­ra Gue­des, a grad­u­ate stu­dent at the Uni­ver­s­ity of Cal­i­for­nia, San­ta Cruz. Gue­des is first au­thor of a pa­per de­tail­ing the find­ings, ac­cept­ed for pub­lica­t­ion by the re­search pub­lica­t­ion As­t­ro­phys­i­cal Jour­nal

“I think the plan­ets are the­re, and it’s worth a try to have a look,” added as­tron­o­mer Greg­o­ry Laugh­lin of the uni­ver­s­ity, a co-au­thor. The in­ves­ti­ga­tors said they ran the re-enactments re­peat­edly with dif­fer­ent start­ing as­sump­tions, and got at least one Earth-sized plan­et each time, and in the hab­it­a­ble zone much of the time.

Most of the 228 plan­ets dis­cov­ered out­side our so­lar sys­tem so far have been found through the Dop­pler meth­od, which an­a­lyzes star­light to de­tect ti­ny wob­bles in a star due to a plan­et’s gravita­t­ional pull. But it’s chal­leng­ing to de­tect rocky, Earth-sized plan­ets be­cause they cause only a ti­ny wob­ble.

But Laugh­lin said sev­er­al fac­tors make Al­pha Cen­tau­ri B an ex­cel­lent can­di­date for find­ing ter­res­tri­al plan­ets. These in­clude the bright­ness of the star and its po­si­tion in the sky, which gives it a long per­i­od of ob­serv­a­bil­ity each year from the South­ern Hem­i­sphe­re. Laugh­lin said it would take five years of watch­ing us­ing a ded­i­cat­ed tel­e­scope to de­tect an Earth-like plan­et around Al­pha Cen­tau­ri B.

Co-au­thor Deb­ra Fisch­er of San Fran­cis­co State Uni­ver­s­ity is lead­ing a pro­gram to in­ten­sively mon­i­tor Al­pha Cen­tau­ri B and neigh­bor­ing Al­pha Cen­tau­ri A. Her team is us­ing the 1.5-meter tel­e­scope at the Cerro Tololo In­ter-A­mer­i­can Ob­serv­a­to­ry in Chile. 

Vis­it­ing any hy­po­thet­i­c aliens in Al­pha Cen­tau­ri would not be an easy proj­ect, de­spite the stars’ rel­a­tive proxim­ity of about 4.36 light-years. A light-year is the dis­tance light trav­els in a year, so it would take about four years for light to get there from he­re. Our fastest space­crafts used to date would take about 60,000 years to go the­re, al­though some sci­en­tists pre­dict new tech­nol­o­gy could re­duce that time con­si­der­ably.

The planet astronomers fingered last year as a po­ten­tial site for life, called Gliese 581c, is about 20.5 light years away. Its ha­bit­a­bi­lity has since come under ques­tion, but some ast­ro­nomers say another planet or­bit­ing the same star might be liveable.  

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An Earth-like, habitable planet may be in our stellar neighborhood, and could be found with a dedicated telescope, new computer simulations suggest. The nearest stars to our Sun are in the three-star system called Alpha Centauri—a popular travel destination in science fiction, though it’s unlikely humans could get there anytime soon. Using simulations based on current planet-formation theories, researchers concluded that Earth-like planets should have formed around one member of this system, the star Alpha Centauri B. One of these, they added, could well be orbiting in the star’s “habitable zone,” a region suitably warm for liquid water to exist on a planet surface. “If they exist, we can observe them,” said Javiera Guedes, a graduate student at the University of California, Santa Cruz. Guedes is first author of a paper detailing the findings, accepted for publication by the research publication Astrophysical Journal. The investigators said they ran the re-enactments repeatedly with different starting assumptions, and got at least one Earth-sized planet each time, and in the habitable zone much of the time. Most of the 228 planets discovered outside our solar system so far have been found through the Doppler method, which analyzes starlight to detect tiny wobbles in a star due to a planet’s gravitational pull. But it’s challenging to detect rocky, Earth-sized planets because they induce only a tiny wobble. But astronomer Gregory Laughlin of the university, a co-author of the report, said several factors make Alpha Centauri B an excellent candidate for finding terrestrial planets. These include the brightness of the star and its position in the sky, which gives it a long period of observability each year from the Southern Hemisphere. Laughlin said it would take five years of watching using a dedicated telescope to detect an Earth-like planet around Alpha Centauri B. Co-author Debra Fischer of San Francisco State University is leading an observational program to intensively monitor Alpha Centauri A and B using the 1.5-meter telescope at the Cerro Tololo Inter-American Observatory in Chile. The researchers hope to detect real planets similar to the ones that emerged in the computer simulations. “I think the planets are there, and it’s worth a try to have a look,” Laughlin said. Visiting any hypothetical aliens in Alpha Centauri would not be an easy project, despite the stars’ relative proximity of 4.35 light-years. A light-year is the distance light travels in a year, so it would take about four years for light to get there from here. Our fastest spacecrafts used to date would take about 60,000 years to go there, although some scientists predict new technology could reduce that time considerably.