A GLOBAL ANALYSIS OF IMPACT CRATERS ON CERES

Michael Zeilnhofer

Advisor: Dr. Nadine Barlow

Committee: Michael Bland, Christopher Edwards, and David Koerner

Department of Astronomy and Planetary Science

4/23/2020

OVERVIEW

• Introduction

• Data Collection • Crater Database• Polygonal Crater Database

• Results• Depth-Diameter Ratio• Simple-to-Complex Transition Diameter • Analysis and Distribution of Crater Morphologies• Analysis and Distribution Polygonal Carters• Global and Regional Ages

• Conclusions

Solarsystem.nasa.gov

INTRODUCTION

• The largest object in the main asteroid belt

• Radius: ≈ 470 km

• Mass: 9.38x1020 kg

• Surface gravity: 0.27 m/s2

• Temperature Range: 110-155 K

Park et al., 2016; Russell et al., 2016

https://solarsystem.nasa.gov/planets/ceres

WHY STUDY CERES

• A primitive asteroid

• Can provide insight into the early solar system

• Mysterious bright spot in HST images (12/03-1/04)

• Ceres has a relatively low density (~2162 𝑘𝑔/𝑚3)

NASA / ESA / J. Parker (Southwest Research Institute) / P. Thomas (Cornell University) / L. McFadden (University of

Maryland, College Park)

DAWN MISSION

• Prior to this mission it was thought Ceres had a minimal number of craters (Bland, 2013)

• Dawn spacecraft went into orbit around Ceres on March 2015

• Dawn revealed a heavily cratered surface (Hiesinger et al., 2016)

Ahuna Mons centered at 10.46º S 315.8º ENASA JPL

WHY STUDY CRATERS

• Craters are a window into a planet/moon’s past

• Craters give insight into the age of a surface and can preserve evidence of ancient and recent processes

• The formation of craters can also give insight into the target material of Ceres

A 7.3-km crater centered at 13.99ºN 2.44ºE Haulani crater (D = 34.0-km) centered at 5.8ºN 10.77ºE

DEPTH-DIAMETER RELATIONSHIP

• Used to determine the simple-to-complex transition diameter (𝐷𝑠𝑐)

• Fresh simple craters typically have a

depth-diameter ratio (d/D)of ~ 1

5(Pike,1977)

• For rocky bodies: 𝐷𝑠𝑐 ∝1

𝑔(Melosh, 1989)

• Ganymede: ~2.0 km (Schenk, 2002) Pike, 1977

CENTRAL PEAKS

• Features found in complex craters

• Found throughout the solar system

• The median peak-to-crater diameter ratio (Dpk/Dc) increases as crustal strength decreases (Barlow et al., 2017)

𝐷𝑐

𝐷𝑝𝑘

A B

A 36.8-km crater centered at

53.19ºS 108.25ºE

AB

CENTRAL PITS

• The pit-to-crater diameter (Dp/Dc) ratio decreases with an increase in gravity and a decrease in volatile content of the crust (Barlow et al., 2017)

• More recent studies suggest that central pit formation is attributed to a weakened subsurface layer (Barlow and Tornabene, 2017)

Barlow et al. 2017

POLYGONAL CRATERS

• Found on rocky and icy bodies (Korteniemi and Öhman, 2014)

• Structurally controlled (Öhman, 2009)

• 1-5x the 𝐷𝑠𝑐 (Öhman, 2009)

Xamba crater (D = 105.0-km) centered at 1ºN, 7ºE

A 36.4-km crater centered at 39.4ºS, 343.6ºE

Rhea Global Color Mosaic (Schenk)

CTX imagesP01_001507_1403_XN_39S016W

B03_010658_1401_XN_39S017WD07_029765_1407_XN_39S016W

POLYGONAL CRATERS

• Found on rocky and icy bodies (Korteniemi and Öhman, 2014)

• Structurally controlled (Öhman, 2009)

• 1-5x the 𝐷𝑠𝑐 (Öhman, 2009)

Xamba crater (D = 105.0-km) centered at 1ºN, 7ºE

A 36.4-km crater centered at 39.4ºS, 343.6ºE

Rhea Global Color Mosaic (Schenk)

CTX imagesP01_001507_1403_XN_39S016W

B03_010658_1401_XN_39S017WD07_029765_1407_XN_39S016W

PROJECT BACKGROUND

• Classify all craters ≥1.0-km

• Determine the 𝐷𝑠𝑐

• Investigate central peak and central pit craters

• Compare central peak and central pit data to other solar system bodies

• Classify polygonal craters (PICs) to further understand the surface properties of Ceres

• Determine regional trends from crater interior morphologies and PICs

• Determine regional ages of the surface from crater counts

Cataloged information:

• Crater ID

• Latitude (°N)

• Longitude (°E)

• Crater diameter in km (𝐷𝐶)

• Minor crater diameter in km

• Ejecta morphologies

• Crater preservation

• Two interior morphologies

• Peak diameter (𝐷𝑝𝑘) in km

• Ratio of peak diameter to crater diameter (𝐷𝑝𝑘/ 𝐷𝐶)

• Pit diameter (𝐷𝑝) in km

• Ratio of pit diameter to crater diameter (𝐷𝑝/𝐷𝐶)

• Crater depth/rim height in km

• Comments

Near-Global Crater Database

METHODOLOGY

• Data were attained from the Dawn spacecraft’s Framing Camera with a resolution of ~400 m/pixel

• High Altitude and Low Altitude Mapping Orbits (HAMO/LAMO)

• The Java Mission-planning and Analysis for Remote Sensing (JMARS) with the LAMO global mosaic of Ceres was used

• The topography models were used to measure crater depth/rim height

EJECTA BLANKETS

• After an impact the falling debris form an ejecta blanket around the crater

• It is generally symmetrical in nature

• Different types of ejecta depending on target

• Ejecta Mobility (EM)Crater Explorer

Timocharis crater (D = 34.1 km) centered at 26.72ºN 346.9ºE displaying a continuousejecta blanket [Image Credit: LROC WAC Global 100 m/px].

A 20.9 km diameter Martian impact crater centered at 5.9°N70.5°E displaying a layered ejecta blanket [Image Credit:

Themis Day IR 100 m global mosaic].

EJECTA BLANKETS

Occator crater (D=92.0 km) centered at 19.82ºN 239.34ºE displaying a continuous ejecta blanket [Images obtained from LAMO].

CRATER PRESERVATION

• Similar to the Martian preservation scale (Barlow, 2004)

• Scale ranges from 0.0-5.0

• 0.0 is a “ghost crater”

• 5.0 is a fresh impact crater Preservation 1.0

A 1.2-km crater centered at 33.42ºS 2.92ºE

Preservation 5.0

Kupalo crater (D = 26.0-km) centered at 39.44ºS 173.20ºE

INTERIOR MORPHOLOGIES

• Interior morphologies classified:

• Bright Albedo (BA) and Dark Albedo (DA) features

• Central Peaks (Pk)

• Central Pits (SP for summit pit and SY for floor pit)

• Floor Deposits (FD)

• Reclassified as Type 1, 2, and 3 lobate flow features

(Buczkowski et al., 2016)

• Wall Terraces (WT)

Occator crater (D = 92.0-km) centered at 19.82ºN 239.34ºE

Haulani crater (D = 34.0-km) centered at 5.8ºN 10.77ºE A 3.6-km crater centered at 27.92ºN 160.77ºE

Bright Albedo Feature (BA) Dark Albedo Feature (DA) Wall Terraces (WT)

Urvara crater (D = 170.0-km) centered at 46.66ºS 249.24ºE

INTERIOR MORPHOLOGIES

A 36.8-km crater centered at 53.19ºS 108.25ºE Nawish crater (D = 77.0 km) centered at 18.28ºN 193.79ºEToharu crater (D = 86.0 km) centered at 48.32ºS 155.95ºE

Central Peak Summit Pit Floor Pit

INTERIOR MORPHOLOGIES

FLOOR DEPOSITS

Type 1 Type 2 Type 3

A 8.2-km crater centered at 14.17ºS 4.40ºEGhanan crater (D=68.0-km) centered at 76.56ºN 30.76ºE A 15.5-km crater centered at 1.40ºS 10.89ºEA 8.0-km crater centered at 2.63ºS 10.65 ºE

A 14.4-km crater centered at 3.88ºS 10.07 ºE

Azacca crater (D = 49.9-km) centered at 6.66ºS 218.40ºE

CRATER DEPTH/RIM HEIGHT

Azacca crater (D = 49.9-km) centered at 6.66ºS 218.40ºE

CRATER DEPTH/RIM HEIGHT

A B

C

D

E

F

A B

DC E F

POLYGONAL CRATER DATABASE

• 4 Categories

• No Structures

• Structures inside of the crater

• Structures outside of the crater

• Structures inside and outside of the crater

Fejokoo crater (D = 68.0-km) centered at 29.15ºN 312.11ºE

N

CRATER AGES

Barlow, 2010 Schmedemann et al., 2014; Hiesinger et al., 2016

RESULTS-OVERVIEW

• 44,594 craters ≥1.0 km in diameter were cataloged in this study

• ~2.1% displayed interior morphologies

• 1,466 polygonal craters (~3.3 % of the total)

• Craters were cataloged from 84.66ºS-89.62ºN and 0º-360ºE

INTERIOR MORPHOLOGIES

Interior Morphology Number of Craters Percentage of all Interior

Morphologies

Bright Albedo Feature (BA) 139 15.2

Dark Albedo Feature (DA) 13 1.4

Floor Deposit (FD) 386 42.1

Central Peak (Pk) 264 28.8

Summit Pit (SP) 4 0.4

Floor Pit (SY) 10 1.1

Wall Terraces (WT) 22 2.4

INTERIOR MORPHOLOGIES

Interior Morphology Number of Craters Percentage of all Interior

Morphologies

Bright Albedo Feature (BA) 139 15.2

Dark Albedo Feature (DA) 13 1.4

Floor Deposit (FD) 386 42.1

Central Peak (Pk) 264 28.8

Summit Pit (SP) 4 0.4

Floor Pit (SY) 10 1.1

Wall Terraces (WT) 22 2.4

FLOOR DEPOSITS

Type of Floor Deposit Number of Craters Percent of All Floor deposits

Type 1 17 4.4

Type 2 207 53.6

Type 3 59 15.3

“Generic Floor Deposits” 63 16.3

Combination Type 2 & 3 40 10.4

FLOOR DEPOSITS

Type of Floor Deposit Number of Craters Percent of All Floor deposits

Type 1 17 4.4

Type 2 207 53.6

Type 3 59 15.3

“Generic Floor Deposits” 63 16.3

Combination Type 2 & 3 40 10.4

CENTRAL PEAK COMPARISON

Mercury Mars Ganymede Ceres

Number of Central Peaks 1764 1682 1080 264

Crater Diameter Range (km) 8.2-251.3 5.0-156.3 7.5-48.6 17.6-260.0

Median Crater Diameter (km) 38.4 10.3 15.2 38.2

Peak Diameter Range (km) 0.8-63.0 0.3-44.5 2.1-23.8 0.5-50.0

Median Peak Diameter (km) 5.5 3.4 5.7 7.5

𝐷𝑝𝑘/𝐷𝑐 Range 0.04-0.60 0.04-0.76 0.11-0.75 0.03-0.48

Median 𝐃𝐩𝐤/𝐃𝐜 0.16 0.32 0.37 0.19

Surface gravity (𝐦/𝐬𝟐) 3.70 3.71 1.43 0.27

Barlow et al., 2017

FLOOR PIT COMPARISON

Barlow et al., 2017

Mars Ganymede Rhea Dione Tethys Ceres

Number of Floor Pits 1144 471 3 1 5 10

Crater Diameter Range (km) 5.0-114.0 12.0-143.8 54.0-230.0 72 11.0-450.0 40.3-155.0

Median Crater Diameter (km) 13.8 38.1 46.1 72 22.5 79.2

𝐷𝑝/𝐷𝑐 Range 0.02-0.48 0.06-0.43 0.17-0.26 0.22 0.13-0.42 0.06-0.25

Median 𝑫𝒑/𝑫𝒄 0.16 0.20 0.27 0.22 0.26 0.13

Surface gravity (𝒎/𝒔𝟐) 3.71 1.43 0.26 0.23 0.15 0.27

SUMMIT PIT COMPARISON

Mercury Mars Dione Ceres

Number of Summit Pits 32 638 2 4

Crater Diameter Range (km) 13.6-47.4 5.1-125.4 20.5-47.0 43.2-96.1

Median Crater Diameter (km) 22.9 14.5 33.8 83.0

𝐷𝑝/𝐷𝑐 Range 0.04-0.12 0.02-0.29 0.15-0.23 0.05-0.10

Median 𝐃𝐩/𝐃𝐜 0.09 0.12 0.19 0.08

Surface gravity (𝐦/𝐬𝟐) 3.70 3.71 0.23 0.27

Barlow et al., 2017

PIC CLASSIFICATION

Polygonal Crater Classification Number of Craters Diameter Range (km)

No Visible Structures 1230 1.0-97.4

Structures Inside of the Crater 3 24.7-55.6

Structures Outside the Crater 222 2.1-155.0

Structures Inside & Outside of the Crater 11 20.8-282.0

PIC CLASSIFICATION

Polygonal Crater Classification Number of Craters Diameter Range (km)

No Visible Structures 1230 1.0-97.4

Structures Inside of the Crater 3 24.7-55.6

Structures Outside the Crater 222 2.1-155.0

Structures Inside & Outside of the Crater 11 20.8-282.0

PLANETARY COMPARISON

Planetary Body ICs PICs % PICs Angle (º)

Mercury1 291 33 11 112

Venus2,3 550 121 22 -

Moon2 656 167 25 -

Mars2,4 1404 236 17 -

Vesta5 90 50 56 134

Rhea5 128 61 48 121

Dione6 3256 1236 37.86 1245

Tethys5 76 56 74 133

Ceres 44594 1466 3.3 121.99±0.25

1. Weihs et al., 2015 2. Öhman, 2009 3. Aittola et al., 2010 4. Öhman et al., 2008 5. Neidhart et al., 2017 6. Beddingfield et al., 2016

• The median Dpk/Dc becomes larger in the northern hemisphere, with the larger values beginning at 40ºN.

• The median Dp/Dc also becomes larger near the north pole indicating the northern hemisphere crust is weaker than that in the southern hemisphere.

• This could be due to a more fractured/brecciated crust and/or higher volatile content in the north.

RESULTS- CENTRAL PEAKS AND PITS

RESULTS- PICS REGIONAL

RESULTS- PICS REGIONAL

RESULTS- CRATER AGES

Asteroid Name Location Age Reference

Eros Amor Group ~2 Ga Chapman et al., 2002

Ida Main Belt~2 Ga

3.35 and 3.6 Ga (LDM)Chapman, 1994

Schmedemann et al., 2014

Itokawa Near Earth 100-1000 Ma O’Brien et al., 2007

Gaspra Main Belt~200 Ma (fresh craters)2.9 Ga (all craters LDM)

Chapman, 1994; 1996Schmedemann et al., 2014

Lutetia Main Belt~3.49 Ga (all craters)

~2.08 Ga (fresh craters)~3.3/3.5 Ga (heavily degraded)

Marchi et al., 2012Schmedemann et al., 2014

Vesta Main Belt

~3.5 Ga Rheasilvia (LDM)~1.0 Ga Rheasilvia (ADM)~3.7 Ga Veneneia (LDM)>2.1 Ga Veneneia (ADM)

~4.0 Pre-Veneneia material (LDM)

~4.2-4.4 Ga Pre-Veneneia material (ADM)

Schmedemann et al., 2014Schenk et al., 2012Marchi et al., 2014William et al., 2014

Ceres Main Belt810-2200 Ma varying crater diameters (LDM) 190-2000 Ma varying crater diameters (ADM)

This study

LDM ADM

RESULTS-CRATER AGES

RESULTS-REGIONAL CRATER AGES

Latitude (º) LDM North (Ma) ADM North (Ma) LDM South (Ma) ADM South (Ma)

80-90 2400±200 530±50 1200±20 320±50

70-80 2600±100 670±40 1300±90 320±20

60-70 2000±1 0 490±20 1200±70 290±20

50-60 1700±70 430±20 800±50 190±10

40-50 1900±70 460±20 870±50 220±10

30-40 1700±60 410±10 780±40 190±9

20-30 1500±50 360±10 840±40 200±10

10-20 1200±40 310±10 700±30 160±8

0-10 1200±40 280±10 870±40 200±8

RESULTS-CENTRAL PEAK AGES

Latitude (º) LDM North (Ga) LDM South (Ga) ADM North (Ga) ADM South (Ga)

80-90 - 3.9−0.10+0.07

- 4.6−0.03+0.01

70-80 2.8−0.6+0.4

0.51±0.30 1.9±0.4 0.46±0.20

60-70 2.6±0.5 1.3±0.4 1.8±0.4 0.90±0.20

50-60 1.5±0.3 2.9−0.8+0.4

1.1±0.2 2.4±0.7

40-50 1.2±0.3 1.4±0.4 0.82±0.20 1.0±0.3

30-40 1.1±0.3 0.45±0.20 0.73±0.10 0.29±0.10

20-30 1.1±0.3 0.68±0.20 0.88±0.20 0.49±0.10

10-20 0.99±0.20 0.45±0.10 0.72±0.20 0.29±0.08

0-10 1.0±0.2 0.55±0.20 0.74±0.20 0.44±0.10

Northern Hemisphere 1.1±0.08 - 0.77±0.06 -

Southern Hemisphere - 0.69±0.07 - 0.49±0.05

Latitude (º) LDM North (Ma) LDM South (Ma) ADM North (Ma) ADM South (Ma)

80-90 1900±400 - 560±100 -

70-80 2100±300 280±100 750±100 88±40

60-70 1600±200 350±90 540±60 120±30

50-60 860±100 380±90 280±40 130±30

40-50 770±90 480±90 260±30 180±30

30-40 350±60 320±60 120±20 100±20

20-30 310±40 390±60 95±10 130±20

10-20 390±50 310±50 120±20 98±20

0-10 440±60 400±50 150±20 120±20

RESULTS-PIC AGES

Latitude (º) LDM North (Ma) LDM South (Ma) ADM North (Ma) ADM South (Ma)

80-90 1900±400 - 560±100 -

70-80 2100±300 280 ± 100 750±100 88±40

60-70 1600±200 350±90 540±60 120±30

50-60 860±100 380±90 280±40 130±30

40-50 770±90 480±90 260±30 180±30

30-40 350±60 320±60 120±20 100±20

20-30 310±40 390±60 95±10 130±20

10-20 390±50 310±50 120±20 98±20

0-10 440±60 400±50 150±20 120±20

RESULTS-PIC AGES

DATASET COMPARISON

• GRaND data shows a higher hydrogen content north of 60°(Prettyman et al., 2017;2019b)

• Topographic difference seen across the northern hemisphere

• Several positive Bouguer anomalies located in the northern hemisphere compared to southern hemisphere (Park et al. 2016). Buczkowski et al., 2016

CONCLUSIONS

• Data suggests a hemispheric difference in crustal strength across Ceres

• Central peaks, central pits, lobate flows and PICs all suggest a weaker crustal strength in the northern hemisphere

• These data are consistent with the Dawn spacecraft observations

• The age data also implies the northern hemisphere is older than the southern hemisphere

CONCLUSIONS

• These results indicate that Ceres has undergone some process (or multiple processes) which have weakened the crust in the north

• Global ocean/”frozen mudball evolution” (Fu et al., 2017; Travis et al., 2018)

• Gardening/mixing of regolith with ice from crust (Prettyman et al., 2019b)

• Volatile-rich crust encompassing a former ocean/frozen ocean or brine pockets (Castillo-Rogez et al., 2020)