The five top places to look for ex­trater­res­trial life

It’s a mighty big uni­verse, but ET hunters are ze­ro­ing in on these prime can­di­dates, re­ports AN­DREW MASTER­SON.

Cosmos - - Digest -

For all the hope and ex­pec­ta­tion, it is sober­ing to re­call that, de­spite the best ef­forts of sci­en­tists and en­gi­neers, there is still no ev­i­dence that life ex­ists any­where be­yond our own planet.

There are, how­ever, some plan­e­tary prime sus­pects. Here are the five places astronomers and as­tro­bi­ol­o­gists think are the best chances for har­bour­ing ET.

LHS 1140b. News of this planet, a “rocky su­per-earth”, was an­nounced in the jour­nal Na­ture in April. Or­bit­ing a red dwarf 39 light-years from Earth, the planet sits in its star’s hab­it­able zone and has an es­ti­mated mass al­most seven times that of our own planet, lead­ing to the as­sump­tion that it com­prises rock en­cas­ing a solid iron core.

Ac­cord­ing to Ja­son Dittmann of the Har­vard Smith­so­nian Cen­tre for Astro­physics in Mas­sachusetts, US, LHS 1140b’s den­sity means it might have sur­vived the run­away global warm­ing thought to de­nude many red dwarf plan­ets. If so, it might now boast a sta­ble at­mos­phere and liq­uid wa­ter.

“This is the most ex­cit­ing ex­o­planet I’ve seen in the past decade,” he said. “We could hardly hope for a bet­ter tar­get to per­form one of the big­gest quests in sci­ence – search­ing for ev­i­dence of life be­yond Earth.”

Enceladus. Thanks to data from NASA’S Cassini space­craft, Saturn’s moon Enceladus has emerged as ev­ery Et-hunter’s favourite tar­get – mainly due to the strong like­li­hood that it fea­tures a subterranean ocean.

In April this year, a team of sci­en­tists from the South West Re­search In­sti­tute (SWRI) in Texas, US, re­vealed a plume of hy­dro­gen erupt­ing from the moon’s sur­face. The plume may well be ev­i­dence of hy­dro­ther­mal vents in the sub­sur­face ocean – the same type of vents that sup­port ex­tremophile life on earth.

“The dis­cov­ery of hy­dro­gen gas and the ev­i­dence for on­go­ing hy­dro­ther­mal ac­tiv­ity of­fer a tan­ta­lis­ing sug­ges­tion that hab­it­able con­di­tions could ex­ist be­neath the moon’s icy crust,” says prin­ci­pal in­ves­ti­ga­tor Hunter Waite.

Ti­tan. An­other of Saturn’s 53 moons, Ti­tan is known to have per­ma­nent hy­dro­car­bon lakes, a ni­tro­gen-heavy at­mos­phere, and pos­si­bly a sub­sur­face ocean be­neath a salty crust. It is a pos­si­ble host for ei­ther wa­ter-de­pen­dent or meth­ane-de­pen­dent life.

Prox­ima-b. This planet, dis­cov­ered in Au­gust 2016, or­bits the star Prox­ima Cen­tauri, 4.2 mil­lion light-years away from our sun, and is the near­est can­di­date be­yond the so­lar sys­tem for host­ing ET.

Re­search in May’s Astron­omy Astro­physics jour­nal found the chances of life ex­ist­ing on the planet may hinge on its or­bital speed.

Astro­physi­cists at the Univer­sity of Ex­eter cal­cu­lated that if Prox­ima-b ro­tates on its axis three times for ev­ery two times it or­bits its sun, then the chances of it be­ing hab­it­able are sub­stan­tially im­proved.

Trap­pist-1. The an­nounce­ment of the Trap­pist-1 sys­tem in Fe­bru­ary, with seven rocky plan­ets or­bit­ing an ul­tra­cool dwarf star, sent rip­ples of ex­cite­ment through as­tro­bi­ol­o­gists ev­ery­where. At least three of the plan­ets looked like they were within the star’s hab­it­able zone.

The lat­est anal­y­sis, by Eric Wolf from the Lab­o­ra­tory for At­mo­spheric and Space Physics at the Univer­sity of Colorado, Boul­der, US, has some­what damp­ened ex­pec­ta­tions, sug­gest­ing that only one of the group has life-sus­tain­ing po­ten­tial. But never mind: one chance in seven is still bet­ter than no chance at all.

“ENCELADUS HAS EMERGED AS EV­ERY ET- HUNTER’S FAVOURITE TAR­GET – MAINLY DUE TO THE LIKE­LI­HOOD IT FEA­TURES A SUBTERRANEAN OCEAN.”

CREDIT: M. WEISS/ CFA

An artist’s im­pres­sion of “rocky su­perEarth” LHS 1140b and its red dwarf host.

CREDIT: ESO/ M. KORNMESSER / GETTY

Artist’s im­pres­sion of the planet or­bit­ing Prox­ima Cen­tauri.

CREDIT: UNI­VER­SAL HIS­TORY ARCHIVE / GETTY IMAGES

Brightly il­lu­mi­nated Enceladus.

CREDIT: NASA

Hov­er­ing over Ti­tan.

CREDIT: NASA

TRAP­PIST-1 Planet Lineup.

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