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AST 309 (11)
Chapter 10

AST 309 Chapter 10: Module 10 Notes

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Department
Astronomy
Course
AST 309
Professor
Finkelstein Keely
Semester
Spring

Description
Module10 Notes Monday, March 27, 2017 11:52 AM Question Over Theory of Lunar Formation • The leading theory forthe moon'sformation: born whena Mar's sized body smackedinto theinfantEarth some4.5billionyearsago ○ If this were the case the moon oughtto bear the chemicalsignature ofboth Earth and its proposed'second' parent. § Buta study suggests the Moon's isotopic compositionreflectsonly Earth's composition • Amassspectrometerwasusedto make themeasurementoftherelative abundanceoftitanium50andtitanium47.Thelunarratioofthetwoisotopesis identical to that foundin Earth's mantle,within4 ppm. ○ Simulations suggest that the second body would havecontributed more than 40%of the moon's bulk, so theratio shouldn't mirror Earthso closely. • Researches haveknown thatthe isotopicratio of oxygen in Moonrocks bearsthe same signatureasEarth'smantle,butbecause oxygen iseasilyvaporized in a collision,itcouldhavebeenreadilyexchangedbetweenEarthandthecloudof vaporandmagmathatwasproducedbytheimpactadcoalescedtoformthe moon,allowingbothbodiestoreachhesameisotopicabundance. ○ But, titanium doesn’tvaporizeas easilyanditwouldhave beenmore difficultforbothbodiestohavereachedthesameratio • The fission model states that theMoonwas spunout of Earth's mantle early on, when the planet'scentrifugalforcemighthaveexceeded itsgravitationalforce • Don’tneed to completelyabandon thecollision model ○ Amore massivesecond body would havesubstantiallyaltered Earth's originalisotopiccomposition,leadingtoanewbornMoonandevolving Earth that are more similar thanin previoussimulations ○ If the moon hadcooledmore slowlythan assumed,the couldhave been time for an exchangeof titanium isotopes betweenthe cloudof vapor and magmaandtheEarth Evaporating Asteroid • Ceres ( a dwarf planetor the largestasteroid in theSolar System) is releasing watervaporfrom itssurfaceata rate ofabout6 kg persecond • Water has beensuspectedof beinga significant component of Ceres for 30years, butonlynowareweidentifyingmoleculesescapingfromtworegionsatthe surface ofthisobject • Ceres and Vestaare bothlocatedin the mainasteroidbeltbetween mars and Jupiterand theirorbitsare close to eachother.Yet,theyare oppositesin termsof compositionandappearance. • Water has beensuspectedof beinga significant component of Ceres for 30years, butonlynowareweidentifyingmoleculesescapingfromtworegionsatthe surface ofthisobject • Ceres and Vestaare bothlocatedin the mainasteroidbeltbetween mars and Jupiterand theirorbitsare close to eachother.Yet,theyare oppositesin termsof compositionandappearance. ○ Vesta hasexperiencedextensivehearing and volcanic eruptionsthat coveredtheentireasteroid ○ Ceres surfaceandinterior havenotreachedtemperatures highenoughto meltrocks • Agreaterabundanceofwaterin Ceresthan in Vesta may have beena crucial factor in producingthe two bodiesradically differentfinalstates ○ The source of thewater vapor maybe related to theprocess of heat dissipationthatprecludedthemeltingofrocksinCeres. ○ One ofproductionmechanismsofwatervaporinvolvesthe meltingof subsurface icethatthenflowsto the surface and evaporatesinto space.The sublimationofwaterice mighthavedissipated theinteriorheatinto space • Ceres mostlikely formed in a colder outer regionof the nascentsolarsystem than vesta, beyondthe snow line Vesta Confirmed as a Venerable Planet Progenitor • Vesta isthe sourceofthe Vestoidfamilyofasteroidsaswellasthe howardite - eucrite0diogenitemeteoritefamily,whichaccountsfor6%ofmeteorites. • The surface compositionof Vesta matches that of the Vestoids,andthat a collisionattheasteroidssouthpolecouldhaveblastedenoughchunksintospace to account forthe Vestoids and meteorites • Vesta assembledonly about2 millionyearsafterthe firstsolidsin the solar system coalesced,and isan originalsurvivoroftheplanet -forming process • Evidence for not just onebut twolarge, overlappingcraters,oneolder
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