Mes­sen­ger’s Pic­tures From Mer­cury Sur­prise Sci­en­tists

The Washington Post - - National News - By Marc Kauf­man

The Mes­sen­ger space­craft that sped past Mer­cury on Jan. 14 sent back pic­tures of a ge­o­log­i­cal for­ma­tion never seen be­fore in the so­lar sys­tem: a cen­tral de­pres­sion with more than 100 nar­row troughs ra­di­at­ing out from it.

Called “The Spi­der” by sci­en­tists an­a­lyz­ing the trove of images and data com­ing back from Mes­sen­ger, the puz­zling fea­ture is the kind of sur­prise that re­searchers live for.

“Mes­sen­ger has sent back data near per­fectly, and some of it con­firms ear­lier un­der­stand­ings, and some of it tells us some­thing brand­new,” said prin­ci­pal in­ves­ti­ga­tor Sean C. Solomon. “The Spi­der is def­i­nitely in the cat­e­gory of some­thing we never imag­ined we’d find.”

Sci­en­tists were also sur­prised by ev­i­dence of an­cient vol­ca­noes on many parts of the planet’s sur­face and how dif­fer­ent it looks com- pared with the moon, which is about the same size. Un­like the moon, Mer­cury has huge cliffs, as well as for­ma­tions snaking hun­dreds of miles that in­di­cate pat­terns of fault ac­tiv­ity from Mer­cury’s ear­li­est days, more than 4 bil­lion years ago.

“It was not the planet we ex­pected,” said Solomon, of the Carnegie In­sti­tu­tion of Wash­ing­ton. “It’s a very dy­namic planet with an aw­ful lot go­ing on.”

Mes­sen­ger passed by Mer­cury af­ter a jour­ney of more than 2 bil­lion miles. It will swing by the planet twice more be­fore set­tling into or­bit around it in 2011.

Mer­cury is among the least un­der­stood plan­ets be­cause its prox­im­ity to the sun makes it hard to visit and to ex­plore. Among the mys­ter­ies re­searchers hope to un­ravel is where and how Mer­cury was formed and the na­ture of the mag­netic fields around it. Earth is the only other planet with such an ac­tive mag­ne­to­sphere.

Solomon said clues into whether Mer­cury once or­bited much farther from the sun, as the­o­rized by many sci­en­tists, may emerge as the craft be­gins to or­bit and con­ducts a chem­i­cal anal­y­sis of the sur­face.

Among the early find­ings is that a crater called Caloris is larger than re­searchers thought af­ter the Mariner 10 space­craft sent back the first images of the planet 33 years ago. Sci­en­tists now be­lieve it is more than 950 miles wide. The Caloris basin, cre­ated by a long-ago as­ter­oid strike, is home to “The Spi­der.”

NASA VIA AS­SO­CI­ATED PRESS

“The Spi­der” is one of the novel for­ma­tions cap­tured by Mes­sen­ger.

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