Mercuryis wracked by intense magnetic disturbances more extremethan any on Earth, new research suggests.
Thesmall, rocky planet also experienced volcanic activity formuch longer than once thought, according to several new studies basedon observationsduring the latest flyby of the small, rocky planet by a NASA spacecraft.
Thenew findings come from data collected by NASA's MESSENGERspacecraft, which unearthedeven more secrets about the closest planet to the sun during its thirdand lastflyby of Mercurylast September. Tostart, the probe discovered Mercury's magnetic field, or"magnetosphere," apparently releases energy in violent magneticdisturbances called substorms far more extreme than comparableones seen on Earth, which include spikes in the size and intensity hereof colorfulauroras and the outermost Van Allen radiation belt.
NASAlaunched MESSENGER in 2004 and it zoomed within 142 miles(229 km) of its Mercury's surface during its most recent flyby. Thecraft,destined to orbit around the planet in 2011, has already yielded atrove ofknowledge, solving mysteriessuch as whetherit hadvolcanoes.[Top 10 MercuryMysteries]
Thescientists detailed their new findings in three papers appearing onlineJuly15 inthe journal Science.
Inone study, researchers scrutinized MESSENGER'sobservations of Mercury's magnetosphere as the planet wasbarraged by the solar wind. They found in the magnetosphere's tail ?the"magnetotail" ? the magnetic field could rise and fall in strength bya factor of two to 3.5 in just two to three minutes.
Magnetosphericphysicist James Slavin at NASA Goddard Space FlightCenter and his colleagues suggest the rapid buildup and release ofenergy seenthere are much like substorms on Earth, but ours accrue 10 times lessenergyand take place over the course of an hour or so.
"Weweren't anticipating anything this strong," Slavintold SPACE.com. "On Mercury, unlike Earth, there's not really anelectricallyconducting ionosphere layer in the atmosphere to limit the electricfieldimposed by the solar wind, and Mercury's proximity to the sun probablypumps ina lot more energy as well."
OnEarth, such magnetic storms interact with the atmosphere and producethe Northern Lights.
Inanother study, the MESSENGER craft found that volcanic activityon Mercurymay havelasted far longer than researchers previously thought.
"Itchanges a lot of our preconceived notions about howMercury might have evolved," planetary scientist Louise Prockter atJohnsHopkins University told SPACE.com.
Prockterand her colleagues analyzed images sent back from MESSENGERof a 180-mile(290-km) impact basin on the planet's surface. This basin, named afterthefamed composer Rachmaninoff, is among the youngest to be observed onthe planetand has exceptionally smooth plains seemingly madeof volcanic materialthat once flowed across the basin's floor.
Thefact these plains are sparsely cratered ? as opposed tolittered with evidence of meteoric impactson Mercuryover theyears ? suggest the volcanism that created the plains must have beenfairlyrecent. The researchers also discovered a depression northeast of thebasinsurrounded by a halo of bright deposits, which they propose to be thelargestvolcanic vent identified on Mercury so far.
Inlight of these findings, Prockter and her colleagues proposethat volcanic activity on Mercury was not only pervasive early in theplanet'shistory, but also lasted up to 2 billion years longer that thought.Under thatproposal, activity would have been under way as recently as 1 to 2billionyears ago.
"UntilMESSENGER, we had expected Mercury to get rid of all its heat early onin itshistory because it's pretty small," Prockter said. "We'll want to seeif the volcanism we see with this basin was an isolated case or whetherit waswidespread across the surface, which would have us perhaps rethinkingourmodels of Mercury. It seems that Mercury did not get rid of her heatnearly asefficiently as had previously been thought."
Scientistsalso found that the very tenuousatmosphere of Mercury,or"exosphere,"made of elements such as magnesium, calcium, and sodium, is apparentlycreatedand maintained by a number of different processes, such as the forcesgeneratedby the planet's magnetic field. These findings help shed light on thecomposition of Mercury's surface and how matter is moved over theplanet.
Thesenew findings are whetting the appetites of scientists forwhen MESSENGER gets into orbit around Mercury.
"It'scertainly surprised me that we learned so much just from flyby data,"Prockter said. "Once we're in orbit, we're going to learn so much more.We've just scratched the surface ? Mercury is even more surprising andinteresting than we thought, and will no doubt continue to be so."
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