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Planet outside our system assigned a color for first time

July 12, 2013
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.

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


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.


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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 the planet’s color 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. “This means that the object that disappeared was blue.” Earlier observations had reported evidence for scattering of blue light on the planet. The latest Hubble observation 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.