live interactive your desktop june 2, 2011 grail: exploring the moon from crust to core presented...
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Presenter: Sami Asmar Co-Investigator & GRAIL Deputy Project Scientist Jet Propulsion Laboratory California Institute of TechnologyTRANSCRIPT
LIVE INTERACTIVE LEARNING @ YOUR DESKTOP
June 2, 2011
GRAIL: Exploring the Moon from Crust to Core
Presented by: Dr. Sami Asmar and Don Boonstra
Exploring the Lunar Interior Structure
Crust To Core Via GRAIL Gravitational Field
Measurements
June 2011
Copyright 2011 California Institute of TechnologyGovernment sponsorship acknowledged
Presenter:
Sami AsmarCo-Investigator &
GRAIL Deputy Project ScientistJet Propulsion Laboratory
California Institute of Technology
The Earth/Moon System
• Moon’s mean radius: 1737 km• Ratio of Moon/Earth radii 1/3.67• Mass ratio of Moon/Earth is 1/81.301• Mean density of the Moon is 3.35 times the density of water
• Saturn floats in water! • Moon’s highest point above mean: +11 km• Moon’s lowest point below mean: -9 km• 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•The day would be eight hours long
•The winds would be much stronger
•Life, if any, might have a different biology
•No honeymoons!
•No lunatics!
•Darker nights
•No lunar calendar
•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
Wieczorek et al. [2006]
Notional view of the lunar interior
Measurement Technique: Differential One-Way Ranging
1
4 3
2
x
x
x
Let’s pause for questions from the audience
crustal densitycrustal thicknesselastic thickness
load densitysurface-subsurface load ratiophase relationship of loads
gravity
topography
geophysical model
internal structure & thermal evolution
geochemistrypetrologygeology
Gravity and topography
-300 +300 mGal
-9 +10 km
Comparing Gravity & TopographyAdmittance & coherence
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
Lithospheric crust, ρc
Lithospheric mantle, ρm
Subsurface load, offset in phase
Surface load SELENE
Kaguya
GRAIL
Kaguya
GRAIL
Let’s pause for questions from the audience
Thermal evolution: heat sources and sinks
External
Heating Impacts
Cooling Radiation
Internal
Heating Radioactivity
Cooling Convection
Reconstruct source/sink contributions throughout geologic time
Deep interior: Structure and state
inner core
McDonald Observatory, TexasRanging to the Moon
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
If we had a good gravity field for the Moon, we could learn a lot. How do we get one?
• Isaac Newton: Motion of satellite around a planet is largely due to the gravity field
• Tracking the motion of a satellite is a good way to measure the gravity field
• Since the Moon always keeps the same face toward the Earth, we cannot track a satellite on the farside directly from the Earth
• But we can track one satellite with another satellite
• This technique was pioneered with the GRACE mission around the Earth in 2002
• GRAIL is the GRACE concept carried to the moon
x Solar Radiation Pressure to <0.001 mGal
x Spacecraft IR Radiation
x 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 programMeasurements:▪ Ka-band ranging measures
relative velocity of the centers of mass of two spacecraft
▪ Links to Deep Space Network for navigation, absolute position, and timing calibration
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 spacecraft system
▪ LM:▪ Spacecraft development & flight
operations▪ GSFC:
▪ Data processing & analysis▪ Sally Ride Science:
▪ Education & outreach cameras
GRAIL Concept
S-band link Telecom/Nav
S-band Timing Code
Ka-band ranging
X-band Radio Science Beacon
Let’s pause for questions from the audience
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
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