Transcript GRAIL - NSTA Learning Center - National Science Teachers

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GRAIL: Exploring the Moon
from Crust to Core
Presented by: Dr. Sami Asmar
and Don Boonstra
June 2, 2011
Exploring the Lunar
Interior Structure
Crust To Core Via GRAIL
Gravitational Field
Measurements
June 2011
Copyright 2011 California Institute of Technology
Government sponsorship acknowledged
Presenter:
Sami Asmar
Co-Investigator &
GRAIL Deputy Project Scientist
Jet Propulsion Laboratory
California Institute of Technology
The Earth/Moon System
•
Moon’s mean radius: 1737 km
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Ratio of Moon/Earth radii 1/3.67
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Mass ratio of Moon/Earth is 1/81.301
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Mean density of the Moon is 3.35 times the density of water
• Saturn floats in water!
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Moon’s highest point above mean: +11 km
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Moon’s lowest point below mean: -9 km
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Moon’s surface area is 3.79x107 km2
• Asia’s surface area: 4.46x107 km2
• Africa: 3.02x107 km2
•
Moon’s age ~4.5 billion years
What if the Moon Did Not Exist?
Contribute your thinking in the Chat
What if the Moon Did Not Exist
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The day would be eight hours long
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The winds would be much stronger
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Life, if any, might have a different biology
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No honeymoons!
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No lunatics!
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Darker nights
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No lunar calendar
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No lecture today
The Moon is moving away (3.8 cm per year)
Great coincidence for perfect solar eclipses
How did Earth get Its Moon?
A. They formed together
in this orbit (accretion)
B. Earth captured the
moon
C.There was a giant
impact
The giant impact and the origin of the Moon
Notional view of the lunar interior
Wieczorek et al. [2006]
Measurement Technique: Differential One-Way Ranging
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1
4
3
x
x
x
Let’s pause for questions
from the audience
Gravity and topography
gravity
-300
+300 mGal
geophysical model
geochemistry
petrology
geology
crustal density
crustal thickness
elastic thickness
load density
surface-subsurface load ratio
phase relationship of loads
topography
internal structure & thermal
evolution
-9
+10 km
Comparing Gravity & Topography
Admittance & coherence
Surface load
SELENE
GRAIL
Lithospheric crust, ρc
Lithospheric mantle, ρm
Subsurface load,
offset in phase
Kaguya
Loading model predicts admittance and
correlation spectra, which depend upon:
crustal density
 mantle density
 crustal thickness
 elastic thickness
 magnitude of surface and
subsurface loads
 phase relationship of loads
GRAIL

Kaguya
Let’s pause for questions
from the audience
Thermal evolution: heat sources and sinks
External
Internal
Heating
 Impacts
Heating
 Radioactivity
Cooling
 Radiation
Cooling
 Convection
Reconstruct source/sink contributions throughout geologic time
Deep interior: Structure and state
Apollo 11 retro-reflector
• GRAIL gravity gives shape model (polar and
equatorial flattening)
• Lunar laser ranging gives physical librations
• Since Apollo era
• Combining the two allows us to deduce the
existence of a lunar core
inner core
McDonald Observatory, Texas
Ranging to the Moon
If we had a good gravity field for the Moon, we
could learn a lot. How do we get one?
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Isaac Newton: Motion of satellite around a planet is
largely due to the gravity field
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Tracking the motion of a satellite is a good way to
measure the gravity field
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Since the Moon always keeps the same face toward the
Earth, we cannot track a satellite on the farside directly
from the Earth
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But we can track one satellite with another satellite
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This technique was pioneered with the GRACE
mission around the Earth in 2002
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GRAIL is the GRACE concept carried to the moon
x
Solar Radiation Pressure to <0.001 mGal
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Spacecraft IR Radiation
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Lunar albedo & Lunar IR
Project Overview
Mission:
• Twin spacecraft launched on a
Delta 2920H-10
• Launch in Sep. 2011
• Short duration of 9-months
• 82 day mapping mission
• Low altitude, polar orbit
• Single payload mission
• Imaging for education program
Institutions:
▪ MIT:
▪ Principal Investigator & Deputy
▪ Science analysis & interpretation
▪ JPL:
▪ Project management, system
engineering, mission assurance,
mission operations, payload
development, science simulations
& modeling, data processing
▪ Contract with Lockheed Martin for
Measurements:
spacecraft system
▪ Ka-band ranging measures
relative velocity of the centers ▪ LM:
of mass of two spacecraft
▪ Spacecraft development & flight
operations
▪ Links to Deep Space Network for
navigation, absolute position,
▪ GSFC:
and timing calibration
▪ Data processing & analysis
▪
Sally Ride Science:
▪
Education & outreach cameras
GRAIL Concept
X-band Radio Science Beacon
S-band link Telecom/Nav
S-band Timing Code
Ka-band ranging
Let’s pause for questions
from the audience
Education Resources
http://solarsystem.nasa.gov/yss
How Long is a Year?
A. About 3 Earth Months
B. About 12 Earth months
C. About 23 Earth months
D. About 164.79 Earth years
E. All of the above
Education Resources
Education Resources
Education Resources
Education Resources
Eyes on Earth 3-D
http://climate.nasa.gov/Eyes/
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