Comet had watery past, scientists find

Comets are of ten called dirt y snow balls be cause they con sist of most ly wa ter ice, pep­pered with rock y de bris and fro zen gas es. Un like as ter oids, ex tra ter res trial chunks made up of rock and min er als, com ets sport a tail – jets of gas and va por that the high-energy par ti cle stream com ing from the sun flushes out of their fro zen bod ies.

“When the ice melted on Wild-2, the re sult ing warm wa ter dis solved min er als that were pres ent at the time and pre cip i tated the i ron and cop per sul fide min er als we ob­served,” Lau ret ta sa id. “The sul fide min er als formed be tween 50 and 200 de grees Cel­si us [122 and 392 de grees Fahren heit], much warm er than the sub-zero tem per a tures pre dicted for the in te ri or of a com et.”

Dis cov ered in 1978 by Swiss as tron o mer Paul Wild, Wild-2 (pro nounced “Vilt”) had trav eled the out er reaches of the so lar sys tem for most of its 4.5 bil lion year his to ry, un­til a close en coun ter with Jupiter's field of grav i ty sent the 3.4 mile-wide com et on to a new, high ly el lip ti cal or bit bring ing it clos er to the sun and the in ner plan ets.

Sci en tists be lieve that like man y oth er com ets, Wild-2 o rig i nat ed in the Kuiper belt, a re gion ex tend ing from be yond Nep tune's or bit in to deep space, con tain ing icy de bris left over from the for ma tion of the so lar sys tem. The find ing of the low-temperature sul­fide min er als may be im por tant for our un der stand ing of how com ets formed, which in turn tells us a bout the or i gin of the so lar sys tem. In ad di tion to pro vid ing ev i dence of liq uid wa ter, re searchers say, the new found in gre di ents put an up per lim it to the tem­per a tures Wild-2 en coun tered dur ing its or i gin and his to ry.