Summary Slides

Geo 50 – October 10, 2012All Summaries Prior to the Midterm

The Moon: History of Exploration Telescopic Phase: Galileo

Photography: Mid-1800’s

Sputnik - 1957

Gagarin - 1961

Kennedy’s National Goal

Space Missions: The US-USSR Space Race• 1959 Luna 3 (Farside)• 1964 Ranger 7, 8, 9• 1966 Luna 9 (Soft Lander)• 1966 Surveyor I, III, V, VI, VII• 1966-1967 Lunar Orbiter I-V• 1969-1972 Apollo 11-17• 1970-1976 Luna 16, 20, 24• 1970 Lunakhod I, II, Zond spacecraft• 1990’s Galileo, Clementine, Lunar Prospector• 2000’s Japanese, US, Indian, Chinese missions

Future Plans• A lunar base? 1969

The Moon - Characteristics and Surface ProvincesCharacteristics Maria Terrae

a. Albedo Low High

b. Elevations Low High

c. Topography Smooth Rough

d. Global distribution

Nearside (17%) Farside (83%)

e. Surface featuresCratersMountainsFaultsTrenchesLava FlowsVolcanoesRidgesSinuous

Channelsf. Composition

The Interior of the Moon Results

• Less Natural Activity than Earth- ~10-20 quakes per year; <2 on Richter Scale- Energy expended ~0.1-10 lbs TNT; (10-7-10-10 of Earth)- Quakes occur at great depth- ~800-1000 km depth on the Moon- ~25 km depth on Earth- No correlation with surface features!- Occur coincident with lunar orbit cycles- Moonquakes are due to tides raised in the Moon by Earth and Sun- Seismic structure:- Revealed three major layers- Crust: 0-60 km; Vp < 6.5 km/sec- Mantle: 60-1400 km Vp ~8 km/sec- Small core? 1400-1700 kmS-waves attenuatedP-waves slower

The Interior of the Moon Implications

• Layering Broadly Similar Between Earth and Moon- Layered interior: Chemical and mechanical

• Important Differences:- Core: Small on the Moon

0.2 lunar radius versus 0.5 Earth radius

- Lithosphere: Thick on the Moon1000 km on the Moon versus 100 km on

EarthWhat are implications for:

Subsidence?Plate Tectonics?

- Relationship of surface provinces.

The Interior of the Moon Results

• Less Natural Activity than Earth- Mechanical layering

- Present: Partially molten at ~800-1000 km Thick lithosphere!!

- Past: What is the thermal evolution??Area: 4π r2

Volume: 4/3π r3

- Positive gravity anomalies in mare- Mascons

- Upper low velocity zone: Origin?- Role of impact cratering?- Megaregolith

The Lithosphere of the Moon Impact Cratering Mechanics

• Energy Partitioning and the Geological Effects

Eh + Ec + Epv + Ee + Es

KEReservoir of Kinetic Energy of Projectile (Velocity, Density, Size)

Impact

HeatingComminution

Plastic/Viscous Deformation

Ejection of Material from Crater

Seismic Waves

Energy Distribution Associated ProcessesEh ≈ 25% Impact Melt, Welding, Metamorphism

Ec ≈ 8% Fragmentation

Epv ≈ 20% Internal Deformation

Ee ≈ 50% Lateral Transport, Mixing, Secondary Cratering

Es << 1% Massive Moonwide Moonquakes, Landslides, Degradation

The Lithosphere of the Moon Lunar Craters and the Cratering Process

• Sources of Information- Natural Earth craters- Explosion craters- Experimental impacts

• Impact Cratering Mechanics- Stages in cratering events- Energy partitioning and the geological

effects

• The Lunar Cratering Record- Morphology of fresh craters- Multi-ringed impact basins

• Summary - Impact Cratering as a Planetary Process

The Lithosphere of the Moon Summary - Impact Cratering as a Process

• Major Source of Energy

• Forms and Modifies Rock Material

• Sculptures Planetary Surfaces

• Major Degradational Process

• Large-Scale Tectonic Process

• Significant Process for Vertical and Lateral Mixing of Materials

• Operates Over Very Short Time Periods, but Influence is Long- Lasting

• Produces Thermal Anomalies

• Significant in Planetary History (Density, Degradation, Flux)

• Role on Planets with Atmospheres and impact on life (?)

The Lithosphere of the Moon Summary - Volcanism as a Process

• 17% of Lunar Surface Covered With Mare Basalt

• Mostly on the Nearside

• Major Depositional Process

• Large Number of Flow Units

• Composition

• Volcanism Active for Long Time

• Thermal Evolution of the Interior

• Ascent and Eruption Style

• Eruption Rates

Lunar Tectonics Summary

• Moon is a one-plate planet.• Very quiet seismically.• Early period of heating and mild expansion.• Mare volcanism in basins, loading, flexure.• Later period of cooling and mild contraction. • Heat loss mechanism is conduction. • Tectonics: Vertical, loading and flexure, not lateral like Earth.

Moon: Insights into the formative years of planetary history. • Ancient age of lunar crust.• Magma Ocean: Concept of wholesale melting. • Linkage of geological observations and accretionary theory.• Moon formed from impact of Mars-sized object into early Earth. • Lunar Interior: Crust, lithosphere and thermal evolution. • Differentiation, segregation instability and overturn. • The Moon as a “one-plate” planet in contrast to Earth.• Impact cratering is a fundamental geological process. • Cometary volatiles may accumulate near poles. • The Moon is a record of the first half of solar system history.

The Lithosphere of Mercury

Impact Craters and Basins:• What is the influence of increased gravity?• Morphology: Looks like lunar farside

- See craters from 100 m to 1000 km- Similar to the Moon but also different

• Changes in crater morphology with increasing diameter- Interior of craters

- Bowl-shaped <10 km- Transitional- Central peaks, flat floors, terraced walls- Interior terracing common: related to gravity?- Depth-diameter relationship

- Exterior of craters- Secondary craters closer to the rim- Density of secondaries higher- Gravity keeps ejecta from travelling far

• Basins- Peak rings at greater than 100 km- Earlier transition than on the Moon

• Role of gravity and impact velocity• Conclusions

The Lithosphere of Mercury Volcanic Activity and Igneous Processes:

• Conclusions- Significant volcanic plains like lunar maria, but flood basalt mode

and no albedo differences.- Different mineralogy?

- Volcanism is very likely to have occurred in intercrater plains. Evidence is somewhat equivocal.

- Could be basin ejecta- Could be flood lavas with no vents

- Explosive volcanic activity: Evidence is seen (pits, pyroclastic deposits): relation to plains?

- Crustal formation processes likely to be different: No anorthositic crust, higher crustal density.

- Primary crust may blend with secondary crust!

The Lithosphere of Mercury Tectonism and Mountain Building:

• No plate boundaries• No strike-slip and lateral offset• No major extension, graben

- Some small graben in Caloris Basin• Some wrinkle ridges in plains• Major global scarps

- Large scale, long- 100’s of km long, 1-2 km high

- Globally distributed- Timing

- After cratered terrain- Synchronous with

smooth plains- Cause

- Global compression- Cooling of lithosphere?- Solidification of core?

• Summary- One-plate planet- A shrinking planet and global scale changes

- Is this how plate tectonics starts?

Mercury: Summary Planetary formational process led to the high metal/silica ratio in

Mercury.

P Geological history of Mercury: Moon-like but materials and processes differ:P Impact crateringP Volcanism: Very extensive, flood basalt style; intercrater plains

likely volcanic. P Tectonism: Global and long-wavelength folding. Origin of plate

tectonics?P Polar Processes: Ice in polar craters. Sources and preserved

record.

What are the radar reflective materials at the poles?

Volatile species and their sources and sinks?: New discoveries on Hollows.

Is Mercury still geologically active? Still an open question!