At­mos­phere de­tected around Earth-like planet

Could sim­i­lar plan­ets ex­ist around other red dwarf stars?

Sky at Night Magazine - - BULLETIN -

The first de­tec­tion of an at­mos­phere around an ex­o­planet with a mass and ra­dius close to that of Earth’s has been made. The planet ap­pears to be rich in wa­ter, rais­ing hopes of one day find­ing a ‘sec­ond Earth’.

The planet, GJ 1132b, is 1.6 Earth masses and 1.4 Earth radii in size, and or­bits a red dwarf star 39 lightyears away. Un­til now as­tronomers have con­cen­trated on ob­serv­ing at­mo­spheres around larger, Jupiter-like plan­ets and su­perEarths. When these plan­ets pass in front of their stars, their large at­mo­spheres block out cer­tain wave­lengths of the starlight, al­low­ing as­tronomers to ex­am­ine the gases that sur­round them.

How­ever, when ob­serv­ing red dwarfs, as­tronomers can ex­am­ine the at­mo­spheres of much smaller plan­ets, as the changes in bright­ness are much clearer against the dim­mer star. Sci­en­tists also have more pre­cise mod­els of red dwarfs than most stars, al­low­ing them to cal­cu­late a star’s size more ac­cu­rately and so work out the size of any plan­ets or­bit­ing them equally well.

It had pre­vi­ously been thought that strong stel­lar ac­tiv­ity could blast away the at­mo­spheres of plan­ets around red dwarfs, how­ever GJ 1132b’s at­mos­phere ap­pears to have sur­vived for bil­lions of years. As these are the most com­mon type of stars in the Galaxy, the find boosts hopes that many more Earth-like plan­ets with at­mo­spheres could be found.

Ini­tial ob­ser­va­tions taken by the Euro­pean South­ern Ob­ser­va­tory’s 2.2m ESO/MPG tele­scope showed that the planet is larger at in­frared wave­lengths, sug­gest­ing that there is wa­ter in the at­mos­phere to make it opaque to this light. But it is likely to be the next gen­er­a­tion of tele­scopes, such as the Gi­ant Mag­el­lan Tele­scope and the James Webb Space Tele­scope, which will con­firm the pres­ence of wa­ter in the planet’s at­mos­phere.

It is un­likely that the planet is hab­it­able since it is only 3.7 mil­lion km from its star – around 10 times the Earth-Moon dis­tance. The high lev­els of ul­tra­vi­o­let ra­di­a­tion at this dis­tance would break the wa­ter apart into hy­dro­gen and oxy­gen.

“On cooler plan­ets, oxy­gen could be a sign of alien life and hab­it­abil­ity. But on a hot planet like GJ 1132b, it’s a sign of the ex­act op­po­site – a planet that’s be­ing baked and ster­ilised,” says Laura Schae­fer from the Har­vard Smith­so­nian Cen­tre for Astro­physics, who took part in the study. www.eso.org

GJ 1132b has an at­mos­phere, but don’t ex­pect life. Its sur­face tem­per­a­ture is a staggering 227ºC

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