astronomy 1010-h planetary astronomy fall_2015 day-27
TRANSCRIPT
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Astronomy 1010-HFall_2015Day-27
Planetary Astronomy
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Course Announcements• How is the sunset/sunrise observing going?
• SW-chapter 7 posted: due Fri. Oct. 30• SW-chapter 8 posted: due Wed. Nov. 4
• Exam-3 Wed. Nov. 4: Ch. 6, 7, 8• I will collect the L-T books on Monday, Nov. 23
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Registration for the Spring semester starts soon so think about taking more astronomy.
ASTR-1010/1011: Planetary Astro & lab (Tell your friends)ASTR-1020/1021: Stellar Astronomy & lab (Reg. + Honors)ASTR-2020: Problems in Stellar AstronomyASTR-3010: History of AstronomyASTR-3040: Intro. To AstroBiologyPHYS-2468: Intro. To Physics Research
ASTR-3030/3031: Instrumentation & Techniques
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Earth’s Moon and the terrestrial planets (Mercury, Venus, Earth, and Mars) have similar and dissimilar properties.
Must be able to explain the differences.
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Comparative planetology: studying planets by comparing them to one another.
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The Earth’s InteriorLayers:
Crust: continents (low density silicates) and basins (basalt: higher iron content).
Mantle.Core (iron, nickel and other dense materials).
Produced by differentiation in the early Earth: dense materials sink; low-density materials rise.
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Geology & Habitatbility
Earth's Interior – Seismic waves Crust – lowest density, Al, Si, Ca Mantle – rocky “plastic” Outer Core – molten Inner Core – solid, Fe, Ni
Earth's Interior – Differentiation Melting and sedimentation of heavy material to core Al26 ==> Mg26 contributed a lot of early heat
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Four processes have shaped Earth: Impact cratering. Tectonism
• modifications of the crust.
Volcanism• igneous activity• magma/lava.
Erosion.
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Material falling from space onto a planet’s surface create impact craters.
Secondary craters can be caused by falling ejecta from the impact.
The Moon and all terrestrial planets experienced this.
Large impacts can melt and vaporize rock.
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Venus and Earth have relatively few craters. Craters on Mars suggest it was once wetter. Mercury and the Moon are covered with
craters.
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Hadean Earth, Dawn of Life
Late Heavy Bombardment – ~3.9 Gyr ago Relatively quiet between formation and LHB Since then, protected by Jupiter
Sterilizing Impacts 350-400 km in diameter
Completely vaporize the oceansGlobal surface temperature rise 2000 C (3600 F)Last ~4.2-3.8 Gyr ago
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The number of craters indicates the surface’s age.
More craters means an older surface and minimal geologic activity.
Tectonism and erosion can erase craters.
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Rocks returned from Moon missions (1969–1976) give ages through radioactive dating.
Almost all cratering happened in the first billion years of the Solar System.
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On the MoonRocks returned in the Apollo missions (1969-
1972) give ages.Rocks from different places show rate of
accretion in the early Solar System.Accretion rate fell sharply after a billion
years.Older surfaces have more craters because
they were formed when the cratering rate was higher.
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Concept QuizThe Moon Long Ago
Imagine taking a picture of the Moon about 2 billion years ago. What would you expect to see?
A. It would have many fewer craters.B. It would have many more craters.C. It would have about as many craters as it does
now.
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Radioactive DatingSome elements can decay from one to
another (e.g., uranium to thorium).These changes take place at known rates.Parent element declines, daughter element
accumulates.Ratio of parent to daughter abundance gives
the age of the rock.Age = time since rock was last molten.