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Herbert V Frey Goddard Space Flight Center

Previously Unrecognized Large Impact Basins on Mars and the Moon: Implications for the Late Heavy Bombardment in the Inner Solar System. Herbert V Frey Goddard Space Flight Center. Workshop on Early Solar System Impact Bombardment Lunar and Planetary Institute 19-20 November 2008.

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Herbert V Frey Goddard Space Flight Center

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  1. Previously Unrecognized Large Impact Basins on Mars and the Moon: Implications for theLate Heavy Bombardment inthe Inner Solar System Herbert V Frey Goddard Space Flight Center Workshop on Early Solar System Impact Bombardment Lunar and Planetary Institute 19-20 November 2008

  2. TWO MAJOR POINTS We have likely significantly underestimated (at least) the large diameter impact inventory of both Mars and the Moon (and therefore of the Earth), and therefore underestimated the likely effects of a Late Heavy Bombardment everywhere Ages of large impact basins on Mars support a Nice-like Late Heavy Bombardment / Terminal Planetary Cataclysm throughout the inner solar system

  3. OUTLINE Evidence for previously unrecognized large impact basins on Mars and the Moon Ages of large impact basins on Mars implications for Mars implications for the inner solar system LHB Mounting evidence for still more large impact basins Future efforts / Caveats, Qualms and Questions

  4. MORE THAN MEETS THE EYE Evidence for previously unrecognized large impact basins on Mars and the Moon

  5. Cassini MOLA shaded relief UNRECOGNIZED IMPACT BASINS ON MARS MOLA data revealed a very large number of probable impact basins on Mars that were not previously known from imagery ? ? “MOLA Hole” Cassini Stretched MOLA topography

  6. 100 KM From Frey et al., GRL 29, No. 10, 10.10291.2001GL013832, 2002 Quasi-Circular Depressions (QCDs) > 50km in the martian lowlands N (D>50 km) = 644 (~90 visible) If the not-visible-on-images QCDs are buried impact basins, then the bulk of the population is “not visible” the lowland crust is much older than we previously thought

  7. “visible” “buried” unrecognizable in MOLA data alone Cassini “MOLA Hole” Mapping QCDs from MOLA data alone will never find all the buried basins All crater retention ages based only on visible + buried QCDs alone are minimum ages, because there are likely many basins are so completely buried they lack topographic expression in MOLA data But more deeply buried basins might have a signature in crustal thickness (from topography AND gravity)

  8. CRUSTAL THICKNESS DATA (Neumann et al.) Circular Thin Areas (CTAs) may be additional buried impact basins Many do correspond to visible or buried Quasi - Circular Depressions (QCDs) [but many do not] Ratio of non-QCD CTAs (possible new basins) to QCDs is greatest in areas of greatest burial (Lowlands, Tharsis) Cumulative frequency curves for the combined QCDs + CTAs (not related to QCDs) are similar to those for QCDs

  9. a b CUMULATIVE FREQUENCY CURVES For visible QCDs, Visible + Buried QCDs, and Visible + Buried QCDs + non-QCD CTAS HIGHLANDS LOWLANDS N(300) N(300) From Edgar and Frey (2008), Geophys. Res. Lett.35, L02201, doi:10.1029/2007GL031466

  10. “AGING” OF THE MARTIAN CRUST How N(300) crater retention ages have changed as more buried basins were counted using topography and crustal thickness data N(300) Crater Retention Ages AREA Vis Vis + Topo Vis + Topo + CT Highlands 0.27 1.98 ( 7.3x) 3.18 ( 1.6x) [11.8x] Lowlands 0.04 0.87 (21.8x) 3.19 ( 3.7x) [79.8x] (Based on Edgar and Frey, 2008, GRL 35, L02201, doi:1029/2007GL031466) Cumulative large diameter cratering on the martian highlands ~ 12 times greater (at least) than originally thought It is likely we have seriously underestimated the early (LHB) cratering on Mars It’s really important to count both visible and buried craters Highlands, Lowlands have same N(300) Crater Retention Age!

  11. If there is a very large population of impact basins on Mars which we did not recognize before we had the MOLA topography…… …..is there also a population of unrecognized impact basins on the Moon that might be revealed by lunar topography (e.g, ULCN2005)?

  12. 260 km 370 km H Grimaldi G Unnamed O A M-R SEARCHING ULCN2005 FOR LUNAR BASINS Left: Default color for ULCN topography. Blue = low. A-DBelow: Progressive stretches of ULCN (top row) with 400 m contours (bottom row). C Below: QCDs > 300 km, solid where identified by Wilhelms, dashed where newly identified in ULCN topography. Upper right: profile (from C) through Grimaldi and unnamed basin. H = Hertzsprung, A = Apollo, O = Orientale, G = Grimaldi, M-R = Mendel-Rydberg A B C D

  13. LUNAR BASINS FOUND IN ULCN2005 (bottom line result #1) The ULCN2005 topography confirms the centers and diameters of many of the basins listed by Wilhelms (1987), but 10 have centers and/or diameters different from those suggested by the topography. 10 on his list are not obvious topographic basins.

  14. LUNAR BASINS FOUND IN ULCN2005 (bottom line result #2) Wilhelms (1987) lists 45 basins > 300 km diameter, described as “distinct”, “probable”, “possible” and “doubtful” basins (at least 10 of which do not have basin topography) We find at least 92 circular topographic basins over the same size range.

  15. (B) (C) D F-S F-S D P D K K Many basins were not “seen” by photogeologists 170W, 10N 170W, 10N Stretched lunar topography with 400 m contours White Circles: Basins listed by Wilhelms: Freundlich-Sharanov (F-S, 600 km) and Korolev (K, 440 km) Black circles: Basins identified in lunar topography, dashed where new. D = definite, P = Probable

  16. A’ A Topographic Profile through Korolev, N of Korolev A A’ 478 km 519 km Unnamed Korolev 3.2 km 4.1 km The unnamed basin north of Korolev is about as large, not quite as deep

  17. Many basins were not “seen” by photogeologists 125W, 45N 125W, 45N Bi Bi D CS CS D Lo Lo D P P Stretched lunar topography with 300 m contours White Circles: Basins listed by Wilhelms: Birkhoff (Bi, 330 km), Coulomb-Sartan (CS, 530 km) and Lorentz (Lo, 360 km) Black circles: Basins identified in lunar topography, dashed where new. D = definite, P = Probable

  18. 120W 0W 240W 120W 0W 240W Wilhelms Basins (White) Compared with Basins from Topography (Black) (newly identified basins shown dashed) More newly identified basins on the far side and at high latitudes

  19. Wilhelms’ list CUMULATIVE FREQUENCY CURVES FOR LARGE LUNAR BASINS Histogram of basin diameters (100 km bins, 200 to 3200 km) N(300) Except for Procellarum, Wilhelms (all) and Frey curves are similar from 1000 down to ~ 500 km Both follow a -2 power law distribution at D = 500 - 800 km Frey’s List (from ULCN) At D <500 km Wilhelms basins fall off the -2 curve (observational loss) Generally expect an exponential increase with decreasing diameter

  20. TOTAL NOT VISIBLE PRELIMNARY Total = Visible, Not Visible, combined Basins > 100 km diameter in SPA identified in ULCN “Total” = “Visible” + “Not Visible” visible = obvious on images not = not obvious on images Total Crater Retention Age (CRA) [e.g., N(100) or N(300)] ~ 1.8 times greater than the Visible CRA

  21. WHAT DOES THIS MEAN? There is a significant and likely large population of previouslyunrecognized large impact basins (and likely smaller craters) on the Moon We have likely under-estimated the total cratering and therefore the early cratering rate on the Moon WHY IS THIS IMPORTANT? Because the lunar cratering rate is the basis for estimating absolute ages on all other planetary bodies

  22. The (Large Diameter) Late Heavy Bombardment on Mars Crater Retention and “Absolute” Ages of the largest impact basins on Mars

  23. 6 new basins identified in crustal thickness data: Amazonis (Az), inside Amazonis (IA), North Tharsis (NT), Sirenum (Si), Solis (So), and SE Elysium (SE) HOW OLD ARE THE LARGEST BASINS ON MARS?(There are ~20 with a diameter > 1000 km) SW Cr Ac Da Si So NP Ut He NT Ag IA Az N POLE S POLE Ac Ut Ut IA Az Cr NT NT Is SE Hm Ar Sc Am Am Ze So Da SW He Ag Si 0, 60W 0, 300W 0, 180W From Frey, 2008, GRL 35, L13103, doi:10.1029/2008GL033515

  24. Highland Basins Lowland Basins Tharsis Basins N(300) AGES FOR LARGE BASINS From counting smaller basins on the rim and interior (both QCDs and non-QCD CTAs > 300 km) Age distribution is peaked! Crustal Thickness 65% of the basins (13 of 20, including 4 of the 5 largest) have an N(300) CRA in the range 2.5-5.0 From Frey (2008) GRL 35, L13103, doi: 10.1029/2008GL033515

  25. H-N Crater Retention Age distribution is peaked! Highland Basins Lowland Basins Tharsis Basins Highland Basins Lowland Basins Tharsis Basins Absolute Age distribution is very peaked! Converting N(300) CRAs to Hartmann-Neukum Model Ages 15/20 (75%) including the 5 largest (D>2500 km) may have formed in only a 100 million year interval. 18/20 (90%) may have formed in a 200 million year interval.

  26. Was the large diameter martian LHB like a “Terminal Lunar Cataclysm” If so, there were very important implications for Mars and for the rest of the inner solar system A “Terminal Martian Cataclysm”?

  27. LHB Life Busters Mars-sized object (Moon-maker) ~6700 km, Crater ? Utopia 3300 km Isidis 1350 km Mars ~6700 Imbrium 1200 km Unnamed ~300 km Moon Hellas 2100 km ~1/2 Large enough to sterilize the planet! Chixulub (Dinosaur-Killer) 10-16 km, Crater~180 km

  28. Highland Basins Lowland Basins Tharsis Basins THERE’S EVEN MORE BAD NEWS The short formation time for most of the largest martian impact basins includes the time when Mars switched from a core magnetic dynamo to no-dynamo state* The dynamo may have shut off in < 50 MY *this work done in collaboration with Rob Lillis Lillis et al. (2008) GRL 35, L14203, doi: 10.1029/GL2008034338

  29. Dynamo No Dynamo Dynamo gone between N(300) = 2.7-3.8 X X BASIN MAGNETIZATION VS AGE The dynamo may have shut off in < 50 (<20?) MY during the peak in large basin formation!!! This work done in collaboration with Rob Lillis, UC Berkeley See: Lillis et al. (2008) GRL 35, L14203, doi: 10.1029/GL2008034338

  30. COINCIDENCE? or CAUSE? • Is the demise of the dynamo in the youngest quarter of the large basin impact interval just a coincidence? • OR • Could formation of 4 of the 5 largest basins (all > 2500 km in diameter) in a relatively short time (< 60 MY?) have actually contributed to the loss of the main magnetic field? • “Too good a coincidence to be one.” • (The possibility of “cause” deserves serious consideration)

  31. COINCIDENCE? or CAUSE? Recent Results Relevant to Death of the Dynamo: Kuang et al. (2008, GRL 35, L14205, doi: 10.1029/GL2008034183) show that a relatively small perturbation (e.g., a 1-2% change in core-mantle boundary heat flow) could kill off the dynamo relatively suddenly if it was already subcritical. Roberts (unpublished results) calculates that the thermal effects of the largest of these impacts (D>2000 km) can produce a 10% or more change in the heat flow across the core-mantle boundary. Disappearance of the global magnetic field on Mars during the period of large basin formation may be more than a coincidence

  32. The period of LHB on Mars was likely catastrophic for several reasons An intense period of large impact formation had enormous environmental consequences sterilization of the surface, loss of atmosphere The global magnetic field disappeared atmosphere no longer protected from solar wind erosion X

  33. What does the large diameter impact spike on Mars imply for the LHB in the rest of the inner solar system? If this is part of an inner solar system-wide event? A “Terminal Martian Cataclysm”?

  34. A “Terminal Martian Cataclysm”? Is this part of an inner solar system-wide event? The interval for peak formation of martian basins is ~ consistent with the Nice model Impact spike (at the Moon) would last ~150-200 MY But the H-N model “absolute” age is wrong: The Late Heavy Bombardment (on the Moon) peaked at ~3.9 BYA If this is part of an inner solar system-wide event It may be possible to tie the lunar & martian chronologies together at ~3.9 BYA

  35. TWO IMPORTANT QUESTIONS ABOUT THE LARGE MARS BASINS AND THEIR AGES Were there really no very large basins before these? Should this peak be at 3.9 BYA? ? If not, then the LHB likely was a short duration “spike”

  36. 30N,120W 30S,0W 30S,240W COULD EVEN OLDER BASINS SURVIVE ON MARS? Present area of large martian basins (even allowing for rings larger than the “diameter” of the basin) leaves a lot of Mars “uncovered” Area of 20 largest basins ~ 43% surface area of Mars (based on diameter of basins) With overlap, ~35 % of Mars is “occupied” by large basins

  37. 1.5D 1.5D 1.5D 30N,120W 30S,0W 30S,240W If large impacts erase the record out to 1.5D (above) or 2.0D (below), less of Mars is available to record earlier ages. At 3D almost no area remains. 2.0D 2.0D 2.0D 30N,120W 30S,0W 30S,240W

  38. 1.5D 1.5D 30S,240W 30S,240W It seems likely that some fraction of the surface area of Mars might be available to retain impacts older than the oldest basin we currently date And there is now a new crustal thickness model (MarsCrust3, Neumann et al., 2008) that should (and does!) reveal even more subtle CTAs

  39. New large CTAs > 500 km diameter Based on a very preliminary study of the new MarsCrust3 crustal thickness model Some of these lie outside the likely effects of the very large basins... …and therefore couldbeolder than the basins already dated. Very, Very Preliminary!!! 30S,0W 1.5D mask 30N,120W 30S,240W

  40. VERY, VERY PRELIMINARY RESULTS Not all of the candidates will survive further study Some are probably NOT additional large impact basins But some may be additional large impact basins, and Some of these are > 1000 km diameter Some lie in possibly older terrain, and have the potential to predate the dated basins It may be possible to determine if there are basins older than those in the narrow interval Can show very preliminary results for 4 cases

  41. N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008)

  42. N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008) NEW CANDIDATE BASINS from MarsCrust3 (Neumann et al., 2008) VERY, VERY PRELIMINARY (and INCOMPLETE)

  43. BACK TO THE MOON Crustal thickness data has revealed a number of new large impact basins on Mars What about lunar crustal thickness data?

  44. Circular Thin Areas revealed in Lunar Crustal Thickness Models from Wieczorick et al. (2006) 0 N, 0W 0 N, 120W 0 N, 240W Blue = Thin crust Red = Thick crust Contour Interval = 4 km

  45. EVIDENCE FOR MORE LARGE LUNAR BASINS? Most visible basins (solid circles) and those identified in ULCN topography (dashed circles) have fairly obvious signatures in crustal thickness data Crustal Thickness 15N, 205W

  46. EVIDENCE FOR MORE LARGE LUNAR BASINS? Most visible basins (solid circles) and those identified in ULCN topography (dashed circles) have fairly obvious signatures in crustal thickness data But there are many CTAs – possible impact basins - not previously identified in the topography alone Crustal Thickness 15N, 205W

  47. Wilhelms (photogeology) Frey QCDs (topography) Frey CTAs (crustal thickness) DISTRIBUTION OF LUNAR BASIN DIAMETERS Shown at same horizontal and vertical scale 100 km Bins (Min = 200, Max = 3400 km) Preliminary!! ~55 new Generally expect a roughly exponential increase in the number of basins with decreasing diameter QCDs + CTAs (topography & crustal thickness)

  48. CUMULATIVE FREQUENCY CURVES FOR LARGE LUNAR BASINS The QCD+CTA curve follows a -2 powerlaw from 600 to 300 km diameter (as does the QCD curve alone) GLOBAL LUNAR N(300) CRAs are Wilhelms = 1.2 QCDs = 2.5 QCDs + CTAs = 3.9 The cumulative large diameter cratering is atleast 3x that previously thought

  49. FUTURE WORK Mars: Determine CRAs for previously recognized, newly found large basins and intra-basin areas using the new crustal thickness data (MarsCrust3) Any basins significantly older than those in the peak? Are intra-basin areas significantly older than basins? Can we date the age of the Borealis Basin? Moon: Determine large diameter CRAs for larger impact basins using ULCN data (down to 100 km?) Do the CRAs cluster and if so, how tightly? Can we determine the spread in (absolute?) ages between SPA and Orientale?

  50. CAVEATS, QUALMS and QUESTIONS The CRAs for the large martian basins are assumed to be formation ages. Maybe they represent global resurfacing ages? Perhaps large impact basin formation at Mars (and the Moon) “wipes out” prior history and we cannot look back beyond the last stages of the LHB So we cannot really tell if it is a short duration impact “spike” as suggested by the Nice model. If the Borealis Basin is real, when it occurred is really important for understanding the LHB history on Mars “Well before” or “just before” the large basin “spike”?

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