Tem­per­a­tures rise 700 de­grees in 6 hours

An ex­traor­di­nar­ily skew or­bit causes ex­treme tem­per­a­ture fluc­tu­a­tions and vi­o­lent winds on the HD 80606b gas gi­ant.

Science Illustrated - - SPACE | PLANETS -

The HD 80606b ex­o­planet or­bits its star in an ex­tremely skew path. When the planet is far­thest away from its star, the dis­tance is 29 times longer than when it is clos­est. The comet-like or­bit means that the planet gets so close to the star that tem­per­a­tures rise from 530 °C to 1,230 °C in only six hours ev­ery 111. days, ac­cord­ing to sci­en­tists from the US Univer­sity of Cal­i­for­nia, Santa Cruz, who base their con­clu­sion on in­frared data from the Spitzer space tele­scope. The sud­den heat­ing makes the at­mos­phere ex­pand tremen­dously, caus­ing pres­sure waves, which trig­ger wind gusts of up to 18,000 km/h. More­over, the ex­pan­sion prob­a­bly means that the up­per at­mos­phere ex­plodes.

Based on the data, as­tronomers can cal­cu­late the con­di­tions on the sur­face of the planet. If an at­mos­phere with a high pres­sure con­tains iron atoms, and if tem­per­a­tures are higher than the melt­ing point of iron, sci­en­tists have strong in­di­ca­tions that iron drops could rain down over the planet. As­tronomers can also pre­dict the wind con­di­tions of the alien plan­ets. Some of the hot Jupiters – gas plan­ets or­bit­ing close to their stars – are locked in a bound ro­ta­tion, so the same side al­ways faces the star. The re­sult is ma­jor tem­per­a­ture dif­fer­ences be­tween the planet’s dark and bright sides. Sci­en­tists can con­vert the dif­fer­ences into ap­prox­i­mate wind speeds. As­tronomers use spec­troscopy to mea­sure wind speeds in an ex­o­planet’s at­mos­phere. In an at­mos­phere char­ac­ter­ized by pow­er­ful wind sys­tems, one half of the at­mos­phere will travel to­wards the ob­server, whereas the other will travel in the op­po­site di­rec­tion. Based on the shift­ing wave- lengths mea­sured via spec­troscopy in both sit­u­a­tions, sci­en­tists can cal­cu­late how quickly the winds have moved the at­mos­phere.

Shield blocks out the light

So far, space tele­scopes such as Ke­pler and Spitzer have pro­duced the most weather fore­cast data, but as the light from the ex­o­plan­ets is only 1/100,000,000 of the star’s, it is a tough job even for the sharpest of tele­scopes.

To make things eas­ier, as­tronomers could try to block out part of the star’s light and study the ex­o­planet’s at­mos­phere di­rectly. For this pur­pose, as­tronomers use a coro­n­a­graph. The de­vice was in­vented in 1931 by French as­tronomer Bernard Fer­di­nand Lyot, who aimed to take a close look at the Sun’s corona. The coro­n­a­graph causes an ar­ti­fi­cial so­lar eclipse by block­ing out the di­rect light from the Sun, so it is pos­si­ble to see the corona.

To­day, as­tronomers use coro­n­a­graphs to search for ex­o­plan­ets or­bit­ing other plan­ets, and NASA’s new pres­ti­gious James Webb tele­scope, which will be launched in 2019, is equipped with a coro­n­a­graph.

Sci­en­tists from NASA’s Jet Propul­sion Lab­o­ra­tory and the God­dard Space Flight Cen­tre have re­cently im­proved coro­n­a­graph ef­fi­ciency. With the new PISCES in­stru­ment – an in­te­gral field spec­tro­graph – sci­en­tists have im­proved the abil­ity to dif­fer be­tween light and dark­ness in a larger por­tion of the wave­lengths that coro­n­a­graph tele­scopes ob­serve, so now they

can see 18 % of the spec­trum as com­pared to the pre­vi­ous 10. Sci­en­tists ex­pect the re­sult to im­prove the abil­ity of the WFIRST (Wide-Field In­frared Sur­vey Tele­scope), which NASA will launch in the mid-2020s, to char­ac­ter­ize ex­o­planet at­mos­pheres – and so weather.

More tele­scopes to study weather

The WFIRST is not alone, as as­tronomers can look for­ward to a con­sid­er­able up­grade of their arse­nal of tele­scopes both on Earth and in space in the years to come.

In the spring of 2019, NASA will launch the James Webb space tele­scope, the suc­ces­sor of the Hub­ble tele­scope, which was launched in 1990. With its 6.5 m mir­ror – as com­pared to Hub­ble’s 2.4 m – James Webb is much more pow­er­ful than its pre­de­ces­sor, and it can be used to find out if the at­mos­pheres of the seven plan­ets in the re­cently dis­cov­ered TRAP­PIST sys­tem in­clude wa­ter. In 2023, NASA will launch another space tele­scope, FI­NESSE, which spe­cial­izes in ex­o­plan­ets. The tele­scope is still on the draw­ing board, but ac­cord­ing to plan, it will study the at­mos­pheres of about 500 ex­o­plan­ets by means of trans­mis­sion spec­troscopy, pro­vid­ing sci­en­tists with new knowl­edge about weather con­di­tions and cli­mate.

Huge, Earth-based tele­scopes are also un­der con­struc­tion, and ac­cord­ing to plan, the ELT (Ex­tremely Large Tele­scope) will be fin­ished in the Ata­cama Desert of Chile in 2024. The ELT, which will be the world’s largest op­ti­cal tele­scope, will have a pri­mary mir­ror with a di­am­e­ter of 39.9 m and will pri­mar­ily search for small, Earth-like plan­ets or­bit­ing other stars. With its huge mir­ror, the tele­scope is 100 times sharper than its pre­de­ces­sors and will be able to take di­rect pictures of the largest plan­ets and their at­mos­pheres.

Soon, as­tronomers will also have ac­cess to the AURA space tele­scope with a 12 m mir­ror. The project is sup­ported by al­most 50 uni­ver­si­ties, and ac­cord­ing to plan, the tele­scope will be launched in the 2030s. It will not only be 100 times more light-sen­si­tive than the Hub­ble tele­scope, it will also have a 25 times higher dis­so­lu­tion. With such a pow­er­ful tele­scope, it will not only be pos­si­ble to de­scribe at­mos­pheres and weather bet­ter than pre­vi­ously, it will also be pos­si­ble to dif­fer be­tween ex­o­plan­ets, which are very much like Earth, and those that just look like it, but are too hot to sup­port bi­o­log­i­cal life. So, as­tronomers might – in the swarm of re­mote, alien plan­ets – be able for the first time to spot a world that does not only have the right cli­mate and per­fect weather con­di­tions, but will also be home to alien life.

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