Previously Unrecognized Large Impact Basins on

Mars and the Moon: Implications for the

Late Heavy Bombardment in

the Inner Solar System

Herbert V FreyGoddard Space Flight Center

Workshop on

Early Solar System Impact Bombardment

Lunar and Planetary Institute19-20 November 2008

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

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

MORE THAN MEETS THE EYE

Evidence for previously unrecognized large impact basins on Mars and the Moon

Cassini

MOLA shaded relief

Stretched MOLA topography

“MOLA Hole”

Cassini

MOLA data revealed a very large number of probable impact basins on Mars that were not previously known from imagery ? ?

UNRECOGNIZED IMPACT BASINS ON MARS

Quasi-Circular Depressions (QCDs) > 50km in the martian lowlands

From Frey et al., GRL 29, No. 10, 10.10291.2001GL013832, 2002

100 KM

N (D>50 km) = 644 (~90 visible)

If the not-visible-on-images QCDs areburied impact basins, then

the bulk of the population is “not visible”

the lowland crust is much older than

we previously thought

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

Cassini “MOLA Hole”

“visible” “buried” unrecognizable in MOLA data

alone

But more deeply buried basins might have a signature in crustal thickness (from topography AND gravity)

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

From Edgar and Frey (2008), Geophys. Res. Lett. 35, L02201, doi:10.1029/2007GL031466

CUMULATIVE FREQUENCY CURVESFor visible QCDs, Visible + Buried QCDs, and

Visible + Buried QCDs + non-QCD CTAS

ba

HIGHLANDS LOWLANDS

N(300)N(300)

“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 underestimatedthe 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!

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)?

GH

O

M-RA

SEARCHING ULCN2005 FOR LUNAR BASINSLeft: Default color for ULCN topography. Blue = low. A-D Below: 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

GrimaldiUnnamed

260 km 370 km

A B C D

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.

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 basinsover the same size range.

D

D

DP

(C)

K

F-S

K

F-S

(B)

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

Many basins were not “seen” by photogeologists

170W, 10N 170W, 10N

Korolev Unnamed

478 km 519 km

A’

A

A A’

4.1 km

3.2 km

Topographic Profile through Korolev, N of Korolev

The unnamed basin north of Korolev is about as large, not quite as deep

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

Many basins were not “seen” by photogeologists

CS

Bi

Lo

CS

Bi

Lo

D

D

D

PP

125W, 45N 125W, 45N

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

CUMULATIVE FREQUENCY CURVES FOR LARGE LUNAR BASINS

Wilhelms’ list

Frey’s List

(from ULCN)

Histogram of basin diameters (100 km bins, 200 to 3200 km)

Generally expect an exponential increase with decreasing

diameter

At D <500 kmWilhelms basins fall

off the -2 curve(observational loss)

Except for Procellarum, Wilhelms (all) and Frey curves are similar from1000 down to ~ 500 km

Both follow a -2 powerlaw distribution atD = 500 - 800 km

N(300)

VISIBLE NOT TOTAL

Basins > 100 km diameter in SPA identified in ULCN

“Total” = “Visible” + “Not Visible”

visible = obvious on imagesnot = not obvious on images

Total Crater Retention Age (CRA)[e.g., N(100) or N(300)] ~ 1.8 times greater than the Visible CRA

Total = Visible, Not Visible, combined

PRELIMNARY

WHAT DOES THIS MEAN?

There is a significant and likely large population of previously unrecognized 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 basisfor estimating absolute ages on

all other planetary bodies

The (Large Diameter) Late Heavy Bombardment on Mars

Crater Retention and “Absolute” Ages of the largest impact basins on Mars

0, 300W 0, 180W

S POLE

0, 60W

N POLE

Ac

Cr

UtNP

IAAz

He

SW

DaSi

Ag

So

He

So

Ag

Cr

Ac

NT

Sc

Is

Ar

IA

Am

Ut

NT

Ut

SEAm

Si

Ze

Hm

SW Da

NT

6 new basins identified in crustal thickness data:Amazonis (Az), inside Amazonis (IA), North Tharsis (NT),

Sirenum (Si), Solis (So), and SE Elysium (SE)

Az

HOW OLD ARE THE LARGEST

BASINS ON MARS?

(There are ~20 with a diameter > 1000 km)

From Frey, 2008, GRL 35, L13103, doi:10.1029/2008GL033515

N(300) AGES FOR LARGE BASINSFrom counting smaller basins on the rim and interior

(both QCDs and non-QCD CTAs > 300 km)

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

Highland Basins

Lowland Basins

Tharsis Basins

Age distribution is peaked!

From Frey (2008) GRL 35, L13103, doi: 10.1029/2008GL033515

Crustal Thickness

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.

Highland Basins

Lowland Basins

Tharsis Basins

Crater Retention

Age distribution is peaked!

Highland Basins

Lowland Basins

Tharsis Basins

Absolute Age distribution is very peaked!

H-N

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”?

Utopia3300 km

Hellas2100 km

Isidis1350 km

Mars-sized object(Moon-maker)

~6700 km, Crater ?

Chixulub (Dinosaur-Killer)10-16 km, Crater~180 km

Mars~6700

Unnamed~300 km

Imbrium1200 km

Moon

LHB Life Busters

Large enough to sterilize the planet!

~1/2

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

Highland Basins

Lowland Basins

Tharsis Basins

BASIN MAGNETIZATION VS AGE

The dynamo may have shut off in < 50 (<20?) MYduring the peak in large basin formation!!!This work done in collaboration with Rob Lillis, UC BerkeleySee: Lillis et al. (2008) GRL 35, L14203, doi: 10.1029/GL2008034338

Dynamo gone

between N(300) = 2.7-3.8 X

Dynamo

No DynamoX

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)

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 Marsduring the period of large basin formation

may be more than a coincidence

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 disappearedatmosphere no longer protected from solar wind erosion

X

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”?

Is this part of aninner 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

A “Terminal Martian

Cataclysm”?

TWO IMPORTANT QUESTIONS ABOUT THE LARGE MARS BASINS AND THEIR AGES

If not, then the LHB likely was a short

duration “spike”

Were there really no

very large basins before these?

Should this peak be at 3.9

BYA?

?

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

COULD EVEN OLDER BASINS SURVIVE ON MARS?

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.

30S,0W

1.5D

30S,240W

1.5D

30N,120W

1.5D

30S,240W

2.0D

30N,120W

2.0D

30S,0W

2.0D

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

30S,240W

1.5D

30S,240W

1.5D

1.5D mask

30N,120W 30S,240W

30S,0W

New large CTAs > 500 km diameter

Based on a very preliminary study ofthe new MarsCrust3

crustal thickness model

Some of these lie outside the likely effects of the

very large basins...

…and therefore could be older than the basins

already dated.

Very, Very Preliminary!!!

VERY, VERY PRELIMINARY RESULTS

Not all of the candidates will survive further studySome are probably NOT additional large impact basins

But some may be additional large impact basins, andSome of these are > 1000 km diameterSome 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

N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES

PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008)

PREVIOUSLY PROPOSED LARGE BASINS (Frey, 2008)

NEW CANDIDATE BASINS from MarsCrust3 (Neumann et al., 2008)

VERY, VERY PRELIMINARY (and INCOMPLETE)

N(300) CRATER RETENTION AGES (CRAs) and DERIVED HARTMANN-NEUKUM MODEL “ABSOLUTE” AGES

BACK TO THE MOON

Crustal thickness data has revealed a number of new large impact basins on Mars

What about lunar crustal thickness data?

0 N, 120W

0 N, 0W

0 N, 240W

Blue = Thin crustRed = Thick crust

Contour Interval = 4 km

Circular Thin Areasrevealed in

LunarCrustal

ThicknessModels

from

Wieczorick et al.(2006)

Most visible basins (solid circles) and those identified in ULCN topography (dashed circles)

have fairly obvious signatures in crustal

thickness data

EVIDENCE FOR MORE LARGE LUNAR BASINS?

15N, 205W

CrustalThickness

Most visible basins (solid circles) and those identified in ULCN topography (dashed circles)

have fairly obvious signatures in crustal

thickness data

EVIDENCE FOR MORE LARGE LUNAR BASINS?

But there are many CTAs – possible

impact basins - not previously identified in the topography

alone15N, 205W

CrustalThickness

DISTRIBUTION OF LUNAR BASIN DIAMETERSShown at same horizontal and vertical scale

100 km Bins (Min = 200, Max = 3400 km)

Frey CTAs

(crustal thickness)

Frey QCDs

(topography)

Wilhelms

(photogeology)

QCDs + CTAs

(topography & crustal thickness)

Generally expect a roughly exponential increase in the

number of basins with decreasing diameter

Preliminary!!~55 new

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 LUNARN(300) CRAs are

Wilhelms = 1.2

QCDs = 2.5

QCDs + CTAs = 3.9

The cumulative large diameter crateringis at least 3x that

previously thought

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?

CAVEATS, QUALMS and QUESTIONSThe 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”?

RECAP: TWO MAJOR POINTSWe have significantly underestimated (at least) the large diameter impact inventory of both Mars [by at least 12x in the highlands] and the Moon [by at least 3x globally] (and therefore of the Earth),

and therefore underestimated the likely effects of a Late Heavy Bombardment everywhere

(Current) Crater Retention and Model Absolute Ages of large impact basins on Mars support a Nice-like Late Heavy Bombardment / “Terminal Planetary Cataclysm” throughout the inner solar system. But….

there are more CRAs to be determined, on known and newly found basins, using the MarsCrust3 CTAs

Thank you!

Back- up Slides

CRATER RETENTION AGE vs BASIN DIAMETER

Isidis has no superimposed basins > 300 km diameter not because it is small, but

because it is young

Isidis1354 km

Sirenum1056 km

Crustal thickness

Crustal thickness

A “relative-to-absolute” age converter

BLACK BOXAGE CONVERTER

Tanaka’s counts for major stratigraphic boundaries were first averaged, then extrapolated to N(300) with a -2 power law, and plotted against averaged Hartman-Neukum “absolute ages” for the same boundaries. The nearly linear relation was fitted and extrapolated to “pre-Noachian” time.

Using the Hartmann-Neukum Model Chronology

Will newly identified CTAs fill in the “deficit” of large martian basins between 500 and 1000 km diameter?

The global cumulative frequency curve fits a -2 power law at both the large and small diameter ends,

but appears to have a “deficit” at the middle (~ 500 – 2000 km) diameters

Combined Cumulative Frequency Curves for the Highlands, Lowlands and Tharsis

N(300) CRAs(Crater Retention Ages)

Highlands: 3.18Lowlands: 3.19

Tharsis: 2.06

The cumulative frequency curves for the Highlands

and the Lowlands are essentially identical

over the range300<D<1000 km

Combined Population = Visible and buried QCDs

+ non-QCD CTAs

Edgar & Frey, 2008

(GRL 35, L02201, doi:1029/2007GL031466)

N(300)

From Edgar and Frey (2008), Geophys. Res. Lett. 35, L02201, doi:10.1029/2007GL031466

TOPOGRAPHIC CHARACTER OF LUNAR BASINS(28 Described by Wilhelms as “Distinct Basins”)

TABLE 1. ULCN CHARACTER OF LUNAR BASINS IDENTIFIED BY WILHELMS (1987)TYPE NAME LAT WEST DIAM TOPOGRAPHIC CHARACTER

LONG (km)DISTINCT South Pole-Aitken -56.0 180.0 2500 Strong basin signatureDISTINCT Imbrium 33.0 18.0 1160 Strong basin signatureDISTINCT Crisium 17.5 301.5 1060 Strong basin signatureDISTINCT Orientale -20.0 95.0 930 Strong basin signatureDISTINCT Australe* -51.5 265.5 880 NO TOPOGRAPHIC BASI NDISTINCT Nectaris -16.0 326.0 860 Strong basin signatureDISTINCT Smythii -2.0 273.0 840 Strong basin signature but smallerDISTINCT Humorum -24.0 39.5 820 Strong basin signatureDISTINCT Keeler-Heaviside* -10.0 198.0 780 Much smaller, offset DISTINCT Serenitatis 27.0 341.0 740 Strong basin signatureDISTINCT Mendel-Rydberg -50.0 94.0 630 offset from DEWDISTINCT Humboldtianum 61.0 276.0 600 strong basin signature but largerDISTINCT Freundlich-Sharonov* 18.5 185.0 600 Strong basin signature, inner ringsDISTINCT Hertzsprung 1.5 128.5 570 Strong basin signatureDISTINCT Ingenii -34.0 197.0 560 Strong basin signatureDISTINCT Coulomb-Sarton 52.0 123.0 530 Strong basin signatureDISTINCT Apollo -36.0 151.0 505 Strong basin signatureDISTINCT Moscoviense 25.0 213.0 445 Strong basin signatureDISTINCT Korolev -4.5 157.0 440 Strong basin signatureDISTINCT Grimaldi -5.0 68.0 430 Strong basin signature but smallerDISTINCT Lorentz 34.0 97.0 360 Strong basin signatureDISTINCT Poincare -57.5 198.0 340 Strong basin signatureDISTINCT Mendeleev 6.0 219.0 330 Strong basin signatureDISTINCT Birkhoff 59.0 147.0 330 Strong basin signatureDISTINCT Schiller-Zucchius -56.0 44.5 325 main is larger than DEWDISTINCT Planck -57.5 224.5 325 Strong basin signature but offsetDISTINCT Schrodinger -75.0 226.0 320 Strong basin signatureDISTINCT Bailly -67.0 68.0 300 Strong basin signature

10 on Wilhelms’ list are not obvious topographic basins!Australe (“distinct”), Tranquilitatis (“probable”) and

8 others (6 “possible”, 2 “doubtful”)

TABLE 1. ULCN CHARACTER OF LUNAR BASINS IDENTIFIED BY WILHELMS (1987)TYPE NAME LAT WEST DIAM TOPOGRAPHIC CHARACTER

LONG (km)

PROBABLE Fecunditatis -4.0 308.0 990 Strong basin signature but offsetPROBABLE Tranquillitatis 7.0 320.0 800 NO TOPOGRAPHIC BASINPROBABLE Mutus-Vlacq -51.5 339.0 690 offset from DEW, largerPROBABLE Nubium -21.0 15.0 690 offset from DEWPROBABLE Lomonsov-Fleming 19.0 255.0 620 slightly offset, smallerPROBABLE Balmer-Kapteyn -15.5 291.0 550 Strong basin signature but offset

possible Procellarum 26.0 15.0 3200 NO TOPOGRAPHIC BASINpossible Tsiolkovskiy-Stark -15.0 232.0 700 Much smaller, offsetpossible Grissom-White -44.0 161.0 600 NO TOPOGRAPHIC BASINpossible Insularum 9.0 18.0 600 NO TOPOGRAPHIC BASINpossible Marginis 20.0 276.0 580 NO TOPOGRAPHIC BASINpossible Flamsteed-Billy -7.5 45.0 570 NO TOPOGRAPHIC BASINpossible Amundsen-Gaswindt -81.0 240.0 355 Strong basin signaturepossible Sikorsky-Rittenhouse -68.5 249.0 310 Moderate basin signaturepossible Pingre-Hausen -56.0 82.0 300 NO TOPOGRAPHIC BASIN

doubtful Al-Khwarismi-King 1.0 248.0 590 NO TOPOGRAPHIC BASINdoubtful Werner-Airy -24.0 348.0 500 NO TOPOGRAPHIC BASIN

TOPOGRAPHIC CHARACTER OF LUNAR BASINS(17 Described by Wilhelms as “Probable, Possible or Doubtful”)

Maximum Scalar Magnetization Within .5R of Basin Center and CRA

0

5

10

15

20

25

30

35

40

45

50

0 1 2 3 4

N(20,10000)

Ma

xim

um

Sc

ala

r M

ag

ne

tiza

tio

n W

ith

in

.5R

of

Ba

sin

Ce

nte

r (n

T)

Visible Basins (Maria)

Visible Basins (Highlands)

QCDs (Highlands)

Nectrais

Nectaris (Highlands only)

QCDs (Maria)

Bodine (2008)(unpublished work)

CRA N(20,10000) = cumulative number > 20 km diameter / 10,000 sq km(visible craters only: most mare basins likely older)

Maximum Scalar Magnetization within 0.5R of Basin CenterVersus Crater Retention Age (CRA)

CRATER RETENTION AGES FOR KNOWN & NEW BASINS

PRELIMINARY!