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ThisisScientificAmerican's 60-secondScience, I'mChristopherIntagliata.
OnJuly 20th, 1969, humankindfinallysetfootonthesurfaceofthemoon. Fiftyyearslaterabigmysteryremains: howtheheckthemoongotthereinthefirstplace.
Fordecades, thethinkinghasbeenthatfourandahalfbillionyearsagoaMars-sizedprotoplanetsmashedintotheEarth. Whenthedustsettled, ourmoonremained, forgedfromthedebrisofEarthandtheotherobject.
Problemis, asscientistshavetakenmoreandmorepreciseisotopicmeasurementsoftheMoonthey'vefoundthatit'snearlyidenticalincompositiontotheEarth—notsomeotherobject.
"AproblemI'vebeenadvertisingasanisotopiccrisis." JayMeloshstudiesplanetaryimpactsatPurdueUniversity. Now, hesays, anewtheoryinthejournalNatureGeosciencemayatleastpointtoawayoutofthatisotopiccrisisofthemoon'schemicalisotopessocloselyresemblingEarth's.
Here'stheidea. Theauthors, ateamofJapanesescientists, writethatmaybeinthoseearlydaysofthesolarsystemtheEarthwassloshingwithoceansofmagma. Then, whentheMars-sizedobjectslammedintothosemoltenseas, theirmodelspredictalotmoreEarth-derivedmaterialgotejectedintoorbitintheformofscorchingvapors.
"Temperaturesoftensofthousandsofdegrees. Andsothatexpandsatspeedsthatexceedtheescapevelocityoftheearth, andinthatwayitinjectsmaterialintoorbitaroundtheEarth."
Thatmaterialrapidlycoalesces, andbingo, you'vegotamoon. Meloshsaystherearestillafewkinkstoworkoutinthescenario. Still, hesays, it'sastepforward.
"Thinkofitasamajorclueinamurdermysteryorsomethinglikethat. Itcouldbeatruecluetowardtheansweroritcouldbeadeception—wedon'tknowyet." Soitcouldbethatwhenastronautsstartedwalkingonthemoonahalf-centuryago, theywerereallyleavingfootprintsontheremainsoftheprimordialEarth.
ThanksforlisteningforScientificAmerican — 60-SecondScience. I'mChristopherIntagliata.