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First-Order Relationships Between Lunar Crater Morphology, Degree of Degradation, and Relative Age: The Crater Degradation Index. William A. Ambrose. Bureau of Economic Geology John A. and Katherine G. Jackson School of Geosciences. Apollo 17 photograph. Outline.

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William A. Ambrose

Bureau of Economic Geology

John A. and Katherine G. Jackson

School of Geosciences

Apollo 17

photograph


Outline

● Cratering Processes

● Crater Type Versus Morphology

-The USGS Main Sequence

● Crater Degradation Processes

-Fracturing, Lava Flooding, Subsequent Impacts

● Crater Degradation Index

-Statistical Trends for Each Crater Type

● Summary and Conclusions


Main Sources and Acknowledgments

NASA & The Lunar and Planetary Institute

-Lunar Orbiter (1966-1968), Apollo (1967-1972)

Clementine (1994), Lunar Prospector (1999)

USGS

-G. K. Gilbert, Eugene Shoemaker, and Don Wilhelms

USAF

-Lunar Aeronautical Charts (1965)

Ralph Baldwin, The Face of the Moon (1949)

Peter Schultz, Moon Morphology (1972)

C. A. Wood, The Modern Moon (2003)

Antonín Rükl, Atlas of the Moon (2004)


Outline

● Cratering Processes

● Crater Type Versus Morphology

-The USGS Main Sequence

● Crater Degradation Processes

-Fracturing, Lava Flooding, Subsequent Impacts

● Crater Degradation Index

-Statistical Trends for Each Crater Type

● Summary and Conclusions


Attributes

Deep Floor

Gentle Profile

Ejecta Blanket

Large Diameter

Langrenus: 144 km across

Typical

Moon Crater

Apollo 8 photograph

Dimensional data: Cherrington (1984)

5 km

2.9 km

LPI

V.E. >25:1


Outline

● Cratering Processes

● Crater Type Versus Morphology

-The USGS Main Sequence

● Crater Degradation Processes

-Fracturing, Lava Flooding, Subsequent Impacts

● Crater Degradation Index

-Statistical Trends for Each Crater Type

● Summary and Conclusions


1

4

5

6

2 & 3

Walled

Plains

Small

Basins

Large

Basins

Simple

Complex

Euler: Type 2

Moltke

Schrödinger

Mare Orientale

227

25

320

10

Schickard

Copernicus:

Type 3

930

93

The Modified USGS Main Sequence

Small

Large

Crater Types (diameter in km)


Type 1 (Simple Craters)

Lunar and Planetary Institute

10 km

Moltke


Type 3 (Aristarchus)

Type 2 (Euler)

40 km

10 km

Types 2 and 3 (Complex Craters)

Lunar and Planetary

Institute


Types 4 and 5

(Walled Plains and Small Basins)

Ptolemaeus (Type 4)

Schrödinger (Type 5)

Apollo 16

Clementine

150 km

75 km

Grimaldi Basin

Type 5

Wood (2003)


Type 6 (Large Basins)

Mare Imbrium

Mare Orientale

Lick Observatory

Lunar Orbiter

900 km

1,300 km

Mare Orientale

Type 6

Wood (2003)


Outline

● Cratering Processes

● Crater Type Versus Morphology

-The USGS Main Sequence

● Crater Degradation Processes

-Fracturing, Lava Flooding, Subsequent Impacts

● Crater Degradation Index

-Statistical Trends for Each Crater Type

● Summary and Conclusions


Data sources:

Observations: >700 primarily nearside craters,

farside craters, small basins and large basins

Crater Degradation Index

● Empirical measurement of crater maturity

based on presence or absence of key

degradation factors.

Maps and photographs:

●Lunar Orbiter, Apollo, Clementine

●Antonín Rükl, Atlas of the Moon (2004)

●Lunar Aeronautical Charts (USAF)

Publications:

●Wood (The Modern Moon, 2003)

●Westfall (Atlas of the Lunar Terminator, 2000)

●Schultz (Moon Morphology, 1972) +many others


Extant?

● Subsequent impacts

-New craters, landslides, and ejecta

Yes

● Lava flooding

-External and internal

No

● Fracturing

No

● Degassing/Volcanism

Maybe

Crater Degradation Factors


Crater Superposition and Relative Age

Overlapping

Non-overlapping

Theophilus

Werner

Cyrillus

Aliacensis

80 km

Lunar Orbiter

Photograph

008


Subsequent Impacts

None

Many

Tycho

Janssen

80 km

100 km


099

Doppelmayer

Lava Flooding:

Mare Humorum

European Southern Obs.

Many large craters in

Mare Humorum are degraded

Gassendi

(floor-fractured)

Degradation is principally

due to mare lavas

Puiseux

Doppelmayer


South

South

Apollo photograph

Gassendi: Floor-fractured crater

European Southern Obs.

100 km

Gassendi


Pu’u O’o Firefountain

Dark-halo

craters

USGS (1985)

Dark-Halo Craters

Alphonsus

Nikolai Kozyrev (1958)

50 km

Apollo photograph


Outline

● Cratering Processes

● Crater Type Versus Morphology

-The USGS Main Sequence

● Crater Degradation Processes

-Fracturing, Lava Flooding, Subsequent Impacts

●Crater Degradation Index

-Statistical Trends for Each Crater Type

● Summary and Conclusions



Copernicus

and Stadius

100 km

Copernicus

(0)

Stadius

(9)


Riccioli

70 km

Degradation From Base Surge Deposits

(Trask and McCauley, 1972)

Lunar Orbiter photograph

(6)

Mare Orientale


y=1.4x+0.6

Crater type versus C.D.I.

10

n=704

9

8

7

mean

6

5

C.D.I.

>100

4

50-100

3

20-50

2

1-20

1

0

1

2

3

4

5

6

Type


C.D.I. distribution per crater type

Type 1

Type 2

40

300

n=403

n=153

30

200

number of craters

number of craters

20

100

10

0

1

2

3

4

5

6

9

0

1

2

3

4

5

6

7

8

9

7

8

C.D.I.

C.D.I.

non-mare

mare


C.D.I. distribution per crater type

Type 3

Type 4

20

10

n=103

n=23

10

number of craters

number of craters

5

0

1

2

3

4

5

6

9

0

1

2

3

4

5

6

7

8

9

7

8

C.D.I.

C.D.I.

non-mare

mare


Langrenus

Wilhelm

Crater type vs. avg. # subsequent impacts

20

n=596

18

16

14

12

10

# impacts

8

non-mare

6

mare

4

2

0

1

2

3

4

5

6

Type


Prevalent flooding

Sinus Iridum

Type 5

Normalized subsequent impact data

10

n=690

9

8

7

6

5

# impacts/ km2 (x 10-3)

4

3

2

1

0

1

2

3

4

5

6

Type


Lunar Crater Densities vs. Time

Number of Craters

per 106 km2

Age (Billions of years)

Modified from Heiken, Vaniman, and French (1991)


C.D.I.

0-1

2

3-4

5-7

>7

Arthur Scale

●Modified from Baldwin (1949, 1963)

Class

Description

Age (109 BY)

0-2.9

1

Fresh rims, rays

2

Freshest post-Mare

3.0-3.4

3

Softened rims

3.5-3.7

4

Heavily degraded

3.8-4.0

5

Faint outline

4.1-4.5


Summary

●Crater morphology is systematically

related to crater size.

●Crater degradation tends to increase

with larger crater type.

●Normalized crater-density values

asymptotically increase for

crater types 1-4; lower for type 5.

●Crossplots of degree of degradation

versus crater type, plus crater-

density data provide a useful

framework for estimating crater

maturity.

Clementine

photograph


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