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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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slide1

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

slide2

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

slide3

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)

slide4

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

slide5

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

slide6

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

slide7

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)

slide8

Type 1 (Simple Craters)

Lunar and Planetary Institute

10 km

Moltke

slide9

Type 3 (Aristarchus)

Type 2 (Euler)

40 km

10 km

Types 2 and 3 (Complex Craters)

Lunar and Planetary

Institute

slide10

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)

slide11

Type 6 (Large Basins)

Mare Imbrium

Mare Orientale

Lick Observatory

Lunar Orbiter

900 km

1,300 km

Mare Orientale

Type 6

Wood (2003)

slide12

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

slide13

● 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

slide14

Extant?

● Subsequent impacts

-New craters, landslides, and ejecta

Yes

● Lava flooding

-External and internal

No

● Fracturing

No

● Degassing/Volcanism

Maybe

Crater Degradation Factors

slide15

Crater Superposition and Relative Age

Overlapping

Non-overlapping

Theophilus

Werner

Cyrillus

Aliacensis

80 km

Lunar Orbiter

Photograph

008

slide16

Subsequent Impacts

None

Many

Tycho

Janssen

80 km

100 km

slide17

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

slide18

South

South

Apollo photograph

Gassendi: Floor-fractured crater

European Southern Obs.

100 km

Gassendi

slide19

Pu’u O’o Firefountain

Dark-halo

craters

USGS (1985)

Dark-Halo Craters

Alphonsus

Nikolai Kozyrev (1958)

50 km

Apollo photograph

slide20

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

slide22

Copernicus

and Stadius

100 km

Copernicus

(0)

Stadius

(9)

slide23

Riccioli

70 km

Degradation From Base Surge Deposits

(Trask and McCauley, 1972)

Lunar Orbiter photograph

(6)

Mare Orientale

slide24

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

slide25

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

slide26

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

slide27

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

slide28

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

slide29

Lunar Crater Densities vs. Time

Number of Craters

per 106 km2

Age (Billions of years)

Modified from Heiken, Vaniman, and French (1991)

slide30

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

slide31

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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