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 Solarsystem.nasa.gov
• Conclusions INTRODUCTION
• The largest object in the main asteroid belt
• Radius: ≈ 470 km
• Mass: 9.38x1020 kg
• Surface gravity: 0.27 m/s2
https://solarsystem.nasa.gov/planets/ceres • Temperature Range: 110-155 K
Park et al., 2016; Russell et al., 2016 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 푘푔/푚3)
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)
NASA JPL Ahuna Mons centered at 10.46º S 315.8º E 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 (퐷푠푐)
• Fresh simple craters typically have a depth-diameter ratio (d/D)of ~ 1 5 (Pike,1977)
1 • For rocky bodies: 퐷 ∝ (Melosh, 1989) 푠푐 푔
• Ganymede: ~2.0 km (Schenk, 2002) Pike, 1977 CENTRAL PEAKS
• Features found in complex craters • The median peak-to-crater diameter ratio (Dpk/Dc) increases as crustal strength decreases (Barlow et al., 2017) • Found throughout the solar system
퐷 푐 B A
A B 퐷푝푘
A 36.8-km crater centered at 53.19ºS 108.25ºE 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 퐷푠푐 (Öhman, 2009)
Xamba crater (D = 105.0-km) A 36.4-km crater centered at centered at 1ºN, 7ºE 39.4ºS, 343.6ºE
CTX images P01_001507_1403_XN_39S016W Rhea Global Color Mosaic (Schenk) B03_010658_1401_XN_39S017W D07_029765_1407_XN_39S016W POLYGONAL CRATERS
• Found on rocky and icy bodies (Korteniemi and Öhman, 2014)
• Structurally controlled (Öhman, 2009)
• 1-5x the 퐷푠푐 (Öhman, 2009)
Xamba crater (D = 105.0-km) A 36.4-km crater centered at centered at 1ºN, 7ºE 39.4ºS, 343.6ºE
CTX images P01_001507_1403_XN_39S016W Rhea Global Color Mosaic (Schenk) B03_010658_1401_XN_39S017W D07_029765_1407_XN_39S016W PROJECT BACKGROUND
• Classify all craters ≥1.0-km • Classify polygonal craters (PICs) to further understand the surface properties of Ceres • Determine the 퐷푠푐
• Determine regional trends from Investigate central peak and central • crater interior morphologies and PICs pit craters
• Determine regional ages of the • Compare central peak and central surface from crater counts pit data to other solar system bodies Near-Global Crater Database
Cataloged information: • Crater ID • Peak diameter (퐷푝푘) in km • Latitude (°N) • Ratio of peak diameter to crater • Longitude (°E) diameter (퐷푝푘/ 퐷퐶)
• Crater diameter in km (퐷퐶) • Pit diameter (퐷푝) in km • Minor crater diameter in km • Ratio of pit diameter to crater • Ejecta morphologies diameter (퐷푝/퐷퐶) • Crater preservation • Crater depth/rim height in km • Two interior morphologies • Comments 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 EJECTA BLANKETS
Timocharis crater (D = 34.1 km) centered at 26.72ºN 346.9ºE displaying a continuous A 20.9 km diameter Martian impact crater centered at 5.9°N ejecta blanket [Image Credit: LROC WAC Global 100 m/px]. 70.5°E displaying a layered ejecta blanket [Image Credit: Themis Day IR 100 m global mosaic]. 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”
A 1.2-km crater centered at 33.42ºS 2.92ºE Kupalo crater (D = 26.0-km) centered at 39.44ºS 173.20ºE • 5.0 is a fresh impact crater Preservation 1.0 Preservation 5.0 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 INTERIOR MORPHOLOGIES
Bright Albedo Feature (BA) Dark Albedo Feature (DA) Wall Terraces (WT)
Haulani crater (D = 34.0-km) centered at 5.8ºN 10.77ºE A 3.6-km crater centered at 27.92ºN 160.77ºE Urvara crater (D = 170.0-km) centered at 46.66ºS 249.24ºE INTERIOR MORPHOLOGIES Central Peak Summit Pit Floor Pit
A 36.8-km crater centered at 53.19ºS 108.25ºE Toharu crater (D = 86.0 km) centered at 48.32ºS 155.95ºE Nawish crater (D = 77.0 km) centered at 18.28ºN 193.79ºE FLOOR DEPOSITS
Type 1 Type 2 Type 3
Ghanan crater (D=68.0-km) centered at 76.56ºN 30.76ºE A 15.5-km crater centered at 1.40ºS 10.89ºE A 8.2-km crater centered at 14.17ºS 4.40ºE A 8.0-km crater centered at 2.63ºS 10.65 ºE A 14.4-km crater centered at 3.88ºS 10.07 ºE CRATER DEPTH/RIM HEIGHT
Azacca crater (D = 49.9-km) centered at 6.66ºS 218.40ºE CRATER DEPTH/RIM HEIGHT
C E
A B
F D
Azacca crater (D = 49.9-km) centered at 6.66ºS 218.40ºE A B
C D 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
N Fejokoo crater (D = 68.0-km) centered at 29.15ºN 312.11ºE 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
퐷푝푘/퐷푐 Range 0.04-0.60 0.04-0.76 0.11-0.75 0.03-0.48
Median 퐃퐩퐤/퐃퐜 0.16 0.32 0.37 0.19 Surface gravity (퐦/퐬ퟐ) 3.70 3.71 1.43 0.27
Barlow et al., 2017 FLOOR PIT COMPARISON
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
퐷푝/퐷푐 Range 0.02-0.48 0.06-0.43 0.17-0.26 0.22 0.13-0.42 0.06-0.25
Median 푫풑/푫풄 0.16 0.20 0.27 0.22 0.26 0.13 Surface gravity (풎/풔ퟐ) 3.71 1.43 0.26 0.23 0.15 0.27
Barlow et al., 2017 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
퐷푝/퐷푐 Range 0.04-0.12 0.02-0.29 0.15-0.23 0.05-0.10
Median 퐃퐩/퐃퐜 0.09 0.12 0.19 0.08 Surface gravity (퐦/퐬ퟐ) 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
RESULTS- CENTRAL PEAKS AND PITS
• 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- PICS REGIONAL RESULTS- PICS REGIONAL RESULTS- CRATER AGES
Asteroid Name Location Age Reference Eros Amor Group ~2 Ga Chapman et al., 2002 ~2 Ga Chapman, 1994 Ida Main Belt 3.35 and 3.6 Ga (LDM) Schmedemann et al., 2014 Itokawa Near Earth 100-1000 Ma O’Brien et al., 2007 ~200 Ma (fresh craters) Chapman, 1994; 1996 Gaspra Main Belt 2.9 Ga (all craters LDM) Schmedemann et al., 2014 ~3.49 Ga (all craters) Marchi et al., 2012 Lutetia Main Belt ~2.08 Ga (fresh craters) Schmedemann et al., 2014 ~3.3/3.5 Ga (heavily degraded) ~3.5 Ga Rheasilvia (LDM) ~1.0 Ga Rheasilvia (ADM) Schmedemann et al., 2014 ~3.7 Ga Veneneia (LDM) Schenk et al., 2012 Vesta Main Belt >2.1 Ga Veneneia (ADM) Marchi et al., 2014 ~4.0 Pre-Veneneia material (LDM) William et al., 2014 ~4.2-4.4 Ga Pre-Veneneia material (ADM) 810-2200 Ma varying crater diameters (LDM) Ceres Main Belt This study 190-2000 Ma varying crater diameters (ADM) RESULTS-CRATER AGES
LDM ADM 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)
+0.07 +0.01 80-90 - 3.9−0.10 - 4.6−0.03 +0.4 70-80 2.8−0.6 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 +0.4 50-60 1.5±0.3 2.9−0.8 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 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
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 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)