BBC Earth (Asia) - - Update -

Three plan­ets dis­cov­ered last year could have liq­uid wa­ter – the key to life as we know it – sloshing around on their sur­faces. The plan­ets sit in the ‘Goldilocks zone’ of TRAPPIST-1, an ul­tra-cool dwarf star lo­cated 40 light-years from Earth in the con­stel­la­tion of Aquar­ius.

In to­tal, four plan­ets in the TRAPPIST-1 sys­tem or­bit within this hab­it­able zone, where the tem­per­a­ture’s just right for liq­uid wa­ter, and life, to ex­ist. Astronomers searched all four plan­ets for a hy­dro­gen-rich and cloud-free at­mos­phere, which would in­di­cate that the plan­ets are likely to be gaseous, like Nep­tune. This type of at­mos­phere was only found on one of the four plan­ets. The other three lacked hy­dro­gen in their at­mos­phere, mean­ing they could hold sur­face wa­ter, just like Earth.

“This dis­cov­ery is an im­por­tant step to­wards de­ter­min­ing if the plan­ets might har­bour liq­uid wa­ter on their sur­faces, which could en­able them to sup­port liv­ing or­gan­isms,” said lead re­searcher Julien de Wit, from the

Mas­sachusetts In­sti­tute of Tech­nol­ogy.

The re­searchers used the Hub­ble Space Tele­scope to mea­sure light emit­ted from the star TRAPPIST-1 as it passed through each of the plan­ets’ at­mos­pheres. As light in­ter­acts with atoms and mol­e­cules in the plan­ets’ at­mos­pheres, slight changes oc­cur in its dis­tri­bu­tion of fre­quen­cies, or spec­trum. By study­ing these changes, the re­searchers were able to de­ter­mine some of the chem­i­cals present in the TRAPPIST plan­ets’ at­mos­pheres.

A few dif­fer­ent pos­si­bil­i­ties ex­ist as to what kind of at­mos­pheres these plan­ets might have, but more pow­er­ful tele­scopes are needed to help us un­der­stand more.

“The next gen­er­a­tion of tele­scopes – in­clud­ing the James Webb Space Tele­scope – will al­low us to probe deeper into their at­mos­pheres,” said lead au­thor Prof Michael Gil­lon, from the Univer­sity of Líege,

Bel­gium. “This will al­low us to search for heav­ier gases such as car­bon, meth­ane, wa­ter, and oxy­gen, which could of­fer biosig­na­tures for life.”

Artist’s im­pres­sion of the TRAPPIST-1 dwarf star, as viewed from one of its plan­ets

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