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Embryonic solar system seen to be brimming with water

Oct. 20, 2011
Courtesy of NASA
and World Science staff

New find­ings sug­gest an em­bry­on­ic so­lar sys­tem con­tains thou­sands of oceans’ worth of wa­ter—so wa­ter-covered plan­ets like Earth may be com­mon, as­tro­no­mers say.

The researchers, us­ing da­ta from the Eu­ro­pe­an Space Agen­cy’s Her­schel Space Ob­serv­a­to­ry, de­tected cold wa­ter va­por en­vel­op­ing a dusty disk around a young star. Disks of this na­ture are be­lieved to be the ma­te­ri­al from which plan­ets even­tu­ally form, or­bit­ing their cen­tral star.

Sci­en­tists pre­vi­ously found warm wa­ter va­por in plan­et-forming disks close to a cen­tral star. But they had­n’t be­fore now de­tected plen­ti­ful wa­ter ex­tend­ing out in­to the cool­er, far reaches of disks, where comets form. Sci­en­tists con­sid­er wa­ter in that re­gion to be im­por­tant be­cause grow­ing ev­i­dence sug­gests a key way that oceans fill up is thanks to icy comets that slam in­to a young plan­et.

“Our ob­serva­t­ions of this cold va­por in­di­cate enough wa­ter ex­ists in the disk to fill thou­sands of Earth oceans,” said as­tron­o­mer Michiel Hoger­hei­jde of Lei­den Ob­serv­a­to­ry in The Neth­er­lands. Hoger­hei­jde is the lead au­thor of a pa­per de­scrib­ing the find­ings in the Oct. 21 is­sue of the jour­nal Sci­ence.

The cen­tral star, called TW Hy­drae, is an es­ti­mat­ed 10 mil­lion years old and lo­cat­ed about 175 light-years away from Earth, in the con­stella­t­ion Hy­dra. A light-year is the dis­tance light trav­els in a year. As­tro­no­mers be­lieve TW Hy­drae and its icy disk may be rep­re­sent­a­tive of many oth­er young star sys­tems, pro­vid­ing new in­sights on how plan­ets with abun­dant wa­ter could form through­out the uni­verse.

Hoger­hei­jde and his team re­ported de­tect­ing a frig­id wa­tery haze that they be­lieve orig­i­nates from ice-coated dust grains near the disk’s sur­face. Ul­tra­vi­o­let light from the star is theo­rized to break some wa­ter mo­le­cules off this ice. That cre­ates a thin lay­er of gas with a light signa­ture de­tected by an in­stru­ment on the satel­lite, a mis­sion in which NA­SA is also in­volved.

TW Hy­drae is an or­ange dwarf star, some­what smaller and cool­er than our yellow-white sun. The disk of ma­te­ri­al en­cir­cling is almost 200 times as wide as the dis­tance be­tween Earth and the Sun. Over the next few mil­lion years, as­tro­no­mers be­lieve mat­ter with­in the disk will col­lide and grow in­to plan­ets, as­ter­oids and oth­er cos­mic bod­ies. Dust and ice par­t­i­cles are ex­pected to as­sem­ble as comets.

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New findings suggest an embryonic solar system contains thousands of oceans’ worth of water—so water-covered planets like Earth may be common, astronomers say. Astronomers using data from the European Space Agency’s Herschel Space Observatory detected cold water vapor enveloping a dusty disk around a young star. Disks of this nature are believed to be the material from which planets eventually form, orbiting their central star. Scientists previously found warm water vapor in planet-forming disks close to a central star. But they hadn’t before now detected plentiful water extending out into the cooler, far reaches of disks, where comets form. Scientists consider water in that region to be important because growing evidence suggests a key way that oceans fill up is thanks to icy comets that slam into a young planet. “Our observations of this cold vapor indicate enough water exists in the disk to fill thousands of Earth oceans,” said astronomer Michiel Hogerheijde of Leiden Observatory in The Netherlands. Hogerheijde is the lead author of a paper describing the findings in the Oct. 21 issue of the journal Science. The central star, called TW Hydrae, is an estimated 10 million years old and located about 175 light-years away from Earth, in the constellation Hydra. A light-year is the distance light travels in a year. Astronomers believe TW Hydrae and its icy disk may be representative of many other young star systems, providing new insights on how planets with abundant water could form throughout the universe. Hogerheijde and his team reported detecting a frigid watery haze that they believe originates from ice-coated dust grains near the disk’s surface. Ultraviolet light from the star breaks some water molecules off this ice, creating a thin layer of gas with a light signature detected by an instrument on the staellite. TW Hydrae is an orange dwarf star, somewhat smaller and cooler than our yellow-white sun. The giant disk of material encircling the star has a size nearly 200 times the distance between Earth and the sun. Over the next few million years, astronomers believe matter within the disk will collide and grow into planets, asteroids and other cosmic bodies. Dust and ice particles are expected to assemble as comets.