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Surprises from smallest planet

Jan. 30, 2008
Staff and wire reports
Updated Jan. 3

A NASA space­craft’s re­cent tou­r near Mer­cu­ry has re­vealed big sur­prises from a plan­et once thought si­m­i­lar to our moon, re­search­ers say. They de­scribe them­selves as amazed by a wealth of im­ages and da­ta show­ing a un­ique world with var­ied ge­o­log­i­cal pro­cesses, and one that may be shrink­ing.

A for­ma­tion dubbed "the spider" on the floor of the Caloris ba­sin, pho­tographed Jan. 14 from MES­SEN­GER. The troughs ema­nat­ing from the mid­dle are thought to be re­sults of a break­ing-up of ma­ter­ials that filled the ba­sin floor after it formed. (Cred­it: NA­SA/Johns Hop­kins Uni­ver­si­ty Ap­plied Phys­ics Lab­o­ra­to­ry/Car­ne­gie Inst. of Wash­ing­ton)


The MES­SEN­GER craft (for MEr­cu­ry Sur­face, Space EN­vi­ron­ment, GE­o­chem­is­try and Rang­ing) reached the plan­et for its first fly­by on Jan. 14 af­ter trav­el­ing more than two bil­lion miles (three bil­lion km) and three years.

The first mis­sion sent to or­bit the plan­et clos­est to our sun, its in­stru­ments col­lect­ed more than 1,200 im­ages and oth­er mea­sure­ments—the first up-close anal­y­sis since the Mar­i­ner 10 craft last flew by in 1975.

“This fly­by al­lowed us to see a part of the plan­et nev­er be­fore viewed by space­craft, and our lit­tle craft has re­turned a gold mine,” said Sean Sol­o­mon of the Car­ne­gie In­sti­tu­tion of Wash­ing­ton, the mis­sion’s prin­ci­pal in­ves­ti­ga­tor.

Un­like our moon, Mer­cu­ry was found to have huge cliffs with struc­tures snak­ing hun­dreds of miles (km) across its face, pre­serv­ing a rec­ord of fault ac­ti­vity pat­terns from its early times, re­search­ers said. It al­so showed im­pact crat­ers very dif­fer­ent from lu­nar ones, they added.

The craft re­vealed an odd fea­ture sci­en­tists dubbed “the spi­der,” un­known be­fore on Mer­cu­ry and un­like an­y­thing on the moon, they said. It lies in the mid­dle of a vast im­pact crat­er called the Caloris ba­sin and con­sists of more than 100 nar­row, flat-floored troughs em­a­nat­ing from a com­plex cen­tral zone.

Another, smaller crater lies near the “spi­der’s” cen­ter, “but wheth­er that crat­er is re­lat­ed to the orig­i­nal forma­t­ion or came lat­er is not clear,” said mis­sion sci­ent­ist James Head of Brown Un­ivers­ity in Rho­de Is­land. The anal­y­sis pro­duced a new, high­er es­ti­mate for the ba­sin’s width (960 miles or 1,550 km) and re­vealed its in­ner plains as dis­tinc­tive and more re­flec­tive than the out­er ones—char­ac­ter­is­tics op­po­site to lu­nar im­pact ba­sins, re­search­ers said.

The mission also provided additional evidence for ridges wide­spread over Merc­ury, which sug­gest the pla­net is con­tract­ing, sci­ent­ists said. They have the­or­ized that as its core cools, it shrinks along with the whole plan­et. That was even an old the­ory for why Earth had moun­tains, but one pro­ven wrong, So­lo­mon said. But with Mer­cury that seems to be the case, re­search­ers said: as the plan­et shrinks, a bit of crust is pushed over an­other. That would form what in­s­tru­ment sci­ent­ist Lou­ise Prock­ter of Johns Hop­kins Uni­ver­sity in Mary­land called “wrin­kle rid­ges.”

Mer­cu­ry’s mag­net­ic field al­so seemed dif­fer­ent from the Mar­i­ner 10 ob­serva­t­ions, sci­en­tists re­ported, and the craft’s in­stru­ments of­fered in­sights in­to the terrain’s min­er­al make­up and out­er at­mos­phere. Two more fly­bys and an in­ten­sive or­bital study are planned. “We are just get­ting started to go where no one has been,” said proj­ect sci­ent­ist Ralph Mc­Nutt of the Ap­plied Phys­ics Lab­o­r­a­to­ry in Lau­rel, Md. A mis­sion web­page with more images, films and in­for­ma­tion is here.

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A NASA spacecraft’s recent tour near Mercury has given scientists a totally new look at a planet once thought similar to our moon, researchers say. Scientists describe themselves as amazed by the wealth of images and data showing a unique world with varied geological processes. The MESSENGER craft (for MErcury Surface, Space ENvironment, GEochemistry and Ranging) reached the planet for its first flyby on Jan. 14 after traveling more than two billion miles (three billion km) and three years. The first mission sent to orbit the planet closest to our sun, its instruments collected more than 1,200 images and other measurements—the first up-close analysis of Mercury since the Mariner 10 craft last flew by in 1975. “This flyby allowed us to see a part of the planet never before viewed by spacecraft, and our little craft has returned a gold mine,” said Sean Solomon of the Carnegie Institution of Washington, the mission’s principal investigator. Unlike our moon, Mercury was found to have huge cliffs with structures snaking hundreds of miles (km) across its face, preserving a record of fault activity patterns from its early times, researchers said. It also showed impact craters very different from lunar ones, they added. The craft revealed an odd feature scientists dubbed “The Spider,” unknown before on Mercury and unlike anything on the moon, they said. It lies in the middle of a big impact crater called the Caloris basin and consists of more than 100 narrow, flat-floored troughs emanating from a complex central zone. “The Spider has a crater near its center, but whether that crater is related to the original formation or came later is not clear,” said mission scientist James Head of Brown University in Rhode Island. The analysis produced a new, higher estimate for the basin’s width (960 miles or 1,550 km) and revealed its inner plains as distinctive and more reflective than the outer ones—characteristics opposite to lunar impact basins, researchers said. Mercury’s magnetic field also appeared to be different from the Mariner 10 observations, scientists said. The craft’s instruments also offered insights into the mineral makeup of the terrain and studied the outer atmosphere, which extends more than 25,000 miles out. Two more flybys and an intensive orbital study are planned. “We are just getting started to go where no one has been,” said project scientist Ralph McNutt of the Applied Physics Laboratory in Laurel, Md.