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Lecture 21

AST 309 Lecture 21: Terrestrial Planets

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Department
Astronomy
Course Code
AST 309
Professor
Finkelstein Keely

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Description
Terrestrial Planets Monday, March 27, 2017 10:57 AM The Four Rocky Planets • Rocky planetsare foundin theinner Solar System • Includingthe Earth • Masses ○ Mercury- 0.055Earths ○ Venus - .82 Earths ○ Earth- 1(6x10^24kg) ○ Mars- .11 Earths Accretion Through Collisions and Sticking • Terrestrial planets likelybeganformingwhenthe gas/icegiant formed, but may havetakenlongertogetuptofinalsize • Terrestrial planets most likelyformed byaccretionprocess ○ Stuff colliding and sticking together § Butlikelihoodfor stickingstillnotfully understood § If dustparticles collide and sticktogether to resultin growth, could getupto1metersizedbodiesinlessthan10,000years, if you have 100%stickingprobability § Some collisionsmay also occur at high speed -sresultingin dust breakingapart,ratherthanstickingtogether Core Accretion -Most Widely Accepted • The core accretionmechanismis still the generally acceptedmechanismfor terrestrial planet formation • Butthis is still a very active area of researchin astronomyrelatedto planet formation • Also need to fullyunderstandwhere the FrostLine is… ○ Terrestrial planets most likelyform interior to thefrost lines, while gas/ice giantslikelyformoutsideofit A Very Active / Dramatic Young Solar System • We have evidencethat the youngSolar System was very active • There were likelydramatic/ chaotic eventsthat shapedthe formationhistories of manyplanets What evidence/observations can you think of that may support the claim that the young solarsystemhad a lotofchaotic/dramatic events? • Formation of themoon (collision ofthe earth created the moon),asteroid belt, • We have evidencethat the youngSolar System was very active • There were likelydramatic/ chaotic eventsthat shapedthe formationhistories of manyplanets What evidence/observations can you think of that may support the claim that the young solarsystemhad a lotofchaotic/dramatic events? • Formation of themoon (collision ofthe earth created the moon),asteroid belt, planetsnotperfectlysmooth Giant Impact as the cause for dichotomy between Mars hemispheres? • One side issmoothofmars,othersidesisvery rocky with a huge crater ○ Smooth side is younger, indicativeof an impact Mercury lost much of its rocky mantle • Unlike Earth,Mercuryonly hasa thinkrockycrustandmantle • Mercury does havea largeiron core • Suggested that mercury mas have lost much of its lighter rocky material dueto catastrophicimpactevents Venus's Odd Rotation • Venusisthe onlyplanetin thesolarsystemto rotateclockwise • One possibleexplanationisthatVenusexperiencedlarge impactearly on,andit mayhavecausedVenustoreverseitsrotationdirection Orientation of Uranus • Uranushasanaxialtiltof97 degrees,soitsaxisofrotationisalmostparallel with the plane ofthesolarsystem • Cause of this maybe due to a large objectthathititand knockeditover • Oreven more recently,researcheshaveshownthatUranusmayhavebeen hitby 2smallerobjectsinsteadofonebigimpact Origin of the Moon • Large size of the moonposesa problemfor planetaryformation scenarios.
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