presented to star astronomy may 1, 2008 by charles j. byrne –image again...
TRANSCRIPT
![Page 1: Presented to Star Astronomy May 1, 2008 By Charles J. Byrne –Image Again –charles.byrne@verizon.net – With topographic views from Nick](https://reader035.vdocuments.mx/reader035/viewer/2022062410/56649e605503460f94b5b883/html5/thumbnails/1.jpg)
• Presented to Star Astronomy
• May 1, 2008
• By Charles J. Byrne– Image Again– [email protected]– www.imageagain.com
• With topographic views from Nick Lordi
The Near Side Megabasin of the Moon
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The Early Moon
• A Mars-sized body, its orbit perturbed, collided with Earth, 4.5 Billion years ago.
• This body, and part of Earth’s crust, were vaporized and formed a ring around Earth.
• Soon, this ring cooled, and the Moon accumulated.
• The heat released by gravity formed a magma ocean.
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Crystallization of the Early Moon
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Asymmetry of the Current Moon
• The “Man in the Moon” (maria) is mostly on the near side
• The near side is low, a bulge on the far side
• The crust is thin on the near side, thick on the far side
• Heavy element anomalies are mostly on the near side
• Uneven moments of inertia: offest C. G.
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Near Side of the Moon
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Far Side (Nozomi)
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Eastern Limb (Lunar Orbiter)
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Eastern Limb (Apollo 16)
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Maps of the Current Moon
• Topography– Photography (photometry and stereo) – Laser and radar altimeters
• Gravity potential– Tracking of spacecraft
• Crustal thickness: inferred from topography and gravity
• Mineral concentrations
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Clementine Elevation Map
-5000-5000 m m 50005000 m m0 0 m m
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Why?
• Asymmetric impacts?
• Uneven crystalization of the magma ocean?
• Tidal effects in a complex early orbit?
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Impact Dynamic Tutorial
• Incoming asteroids and comets
• Hypervelocity impacts: explosions
• Cavity formation
• Ejected target material
• Formation of rings
• Effects of target curvature
• Scaling laws
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Lunar Basin (Orientale)
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Orientale, LIDAR and ULCN (Lordi)
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Noise Reduction for ULCN (Lordi)
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Orientale, ULCN (Lordi)
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Orientale, radial profile
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Simulation of Impacts
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Radial Profile of Selected Basins
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Profile of Ejection Velocity
0
1
2
3
4
5
6
0.2 0.4 0.6 0.8 1
Normalized Internal Radius
Vel
oci
ty
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Curvature of the Target
• A giant basin must consider the spherical nature of its target
• Ejecta is thrown into elliptical orbit
• There is less area for the ejecta to land near the antipode, so it piles up
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Steps in Making the Model
• “Flat Moon” basin model
• Ejection velocity radial profile
• Orbital trajectory equations
• Focusing effect of the spherical Moon
• Final radial profile of ejecta
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The Search
• The scaled model has these parameters:– Latitude and Longitude of center– Diameter– Depth
• Parameters were varied to make a best fit• Started with two large basins• They grew as the fit improved• They merged into one giant basin
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Model of the Near Side Megabasin
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600 km600 kmimpactorimpactor
EscapingEscapingejecta (hyperbola)ejecta (hyperbola)
EscapeEscapevelocityvelocity
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Velocity lessVelocity lessthan escapethan escape
Ejecta Ejecta passes passes antipodeantipode
Transientcraterexpands
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Velocity fallsVelocity fallsfurtherfurther
Ejecta is Ejecta is concentratedconcentratedat antipodeat antipode
Antipode
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Velocity fallsVelocity fallsfurtherfurther
Ejecta falls betweenEjecta falls betweenbasin rim and antipodebasin rim and antipode
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Radial Profile of the Near Side Megabasin
-8000
-6000
-4000
-2000
0
2000
4000
6000
8000
10000
0 1000 2000 3000 4000 5000 6000
Radius, center to antipode (km)
De
pth
(m
)
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The NSM Floor is Refilled with Crust
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Refilling of Plastic Crust
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Model of the Moon with the NSM
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The NSM and its Antipode
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NSM and Titanium
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NSM and Iron
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NSM and Thorium
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NSM and Maria
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NSM Rim on the Far Side
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NSM Rim at Tsiolkovskiy
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Summary
• The history of the Moon from its origin to today has been reviewed
• Its original crust has been strongly modified by impacts, starting with the NSM and SPA.
• 4 billion years of bombardment followed• The major mineral anomalies on the surface
are associated with the impacts of the NSM and SPA.
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