Courtesy of NASA and World Science staff

As­tro­no­mers us­ing NASA’s Hub­ble Space Tel­e­scope say they have fig­ured out the col­or of a plan­et out­side our so­lar sys­tem for the first time.

It’s co­balt blue, though not at all Earth-like, they said, de­scrib­ing a world where sur­face tem­per­a­tures are hot enough to melt stone and where it may rain glass—side­ways. The plan­et is HD 189733b, one of the clos­est worlds out­side our so­lar sys­tem vis­i­ble cross­ing the face of its star, 63 light-years away. A light-year is the dis­tance light trav­els in a year.

Hub­ble’s Space Tel­e­scope Im­ag­ing Spec­tro­graph, which an­a­lyzes light, meas­ured changes in color com­ing from the plan­et’s lo­ca­tion be­fore, dur­ing and af­ter a pass be­hind its star. There was a slight drop in light and col­or change, sci­en­tists said.

“Light was mis­sing in the blue [part of the spec­trum] but not in the red when it was hid­den,” ex­plained re­search team mem­ber Fred­er­ic Pont of the Uni­vers­ity of Ex­e­ter in South West Eng­land. So “the ob­ject that dis­ap­peared was blue.”

Ear­li­er ob­serva­t­ions had re­ported ev­i­dence for scat­ter­ing of blue light on the plan­et. The lat­est work would con­firm that. On this tur­bu­lent al­ien world, sci­en­tists say, the day­time tem­per­a­ture is nearly 2,000 de­grees Fahr­en­heit (1,100 Cel­sius), and it pos­sibly rains glass side­ways in howl­ing, 4,500-mph (7,200-kph) winds.

The co­balt blue comes not from the re­flec­tion of a trop­i­cal ocean as it does on Earth, they add, but rath­er a ha­zy, blow-torched at­mos­phere con­tain­ing high clouds laced with sil­i­cate par­t­i­cles. Sil­i­cates con­dens­ing in the heat could form very small drops of glass that scat­ter blue light more than red light.

Hub­ble and oth­er ob­servatories have in­ten­sively stud­ied HD 189733b and found its at­mos­phere to be change­a­ble and ex­ot­ic.

It’s among a bi­zarre class of plan­ets called hot Jupiters, which cir­cle pre­car­i­ously close to their par­ent stars. The new ob­serva­t­ions yield new in­sights in­to the make­up and cloud struc­ture of the whole class, ac­cord­ing to in­ves­ti­ga­tors. The plan­et was first iden­ti­fied in 2005 and or­bits an es­ti­mat­ed 2.9 mil­lion miles (4.6 mil­lion km) from its par­ent star, so close that it’s tid­ally locked—the same side al­ways faces the star.

In 2007, NASA’s Spitzer Space Tel­e­scope meas­ured the in­fra­red light, or heat, from the plan­et, lead­ing to one of the first tem­per­a­ture maps for plan­et out­side our sys­tem. The map shows day side and night side tem­per­a­tures on HD 189733b dif­fer by about 500 de­grees Fahr­en­heit (280 Cel­sius). This is ex­pected to cause fierce winds to roar from the day side to the night side.

PHOTO: Artist’s impres­sion of HD 189733b (Cour­tesy NA­SA, ESA, and G. Ba­con (STScI))

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