Mars/moon impact rate ratio:2000/2012 comparison

• Impact craters as a link to other terrestrial planets, satellites and asteroids

• Interplanetary comparisons• Mars/Moon impact ratio

Boris IvanovInstitute for Dynamics of Geospheres, RAS, Moscow

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ASTEROIDS

• Stony (several types)• Iron• Orbit evolution due to

close encounters and resonances with giant planets

• No close encounters with Jupiter (Tisserand T_J>3)

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COMETS

• Jupiter family (JFC): mostly from Kuiper Belt

• 2<T_J <3

• Long-periodic comets (LPC) drop out of Oort cloud

• Unpredictable (number of returns?)3MS3 IKI 2012

Crater chronology: interplanetary comparison

Moon: crater counts and chronology by returned samples

Moon crossers orbits - > impact velocity and probability

Scaling laws: D_crater -> D_projectile

Mars crossers orbits - > impact velocity and probability, relative number of projectiles

Scaling laws: D_projectile -> D_crater

Mars: crater counts (beware of secondaries!) Mars: model chronology

Bolide ratioRb

Of numbers of impacts of the same size bodies per 1 km2 per 1 year

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2012 astorb.dat

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The Moon (Earth) crossers Mars-crossers H<18 H<16 H<18 H<16

Asteroid-like orbits TJ > 3 N 458 82 5774 1416 Pcol, yr-1 0.16×10-9 0.14×10-9 0.23×10-9 0.17×10-9 <Uimp> 17.0 19.0 9.3 10.0

JFComet-like orbits 2< TJ <3

N (% of total) 97 (17%) 18 (25%) 336 (5.5%) 83 (5.5%) Pcol, yr-1 0.051×10-9 0.045×10-9 0.07×10-9 0.06×10-9 <Uimp> 23.4 25.5 17.3 16.7

(1) the percentage of comet-like orbits (higher impact velocities) on the Moon is about 25% to 20%, on Mars this number is factor of ~2 less;

(2) at the modern Mars orbit (e=0.094) the “bolide ratio” (the ratio of impact number per

unit area per unit time) is about Rb=5.5 in comparison with 2000 estimates of

Rb=4.9(3) the average impact velocity for asteroid-like objects on the moon increases to ~19

km/s in comparison with 16.1 km/s in 2000 estimates.

Population of asteroid-like (TJ>3) and comet-like orbits (TJ<3)2005 vs. bolide survey

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Below D~1 km (H~18) population of small (10 cm) projectiles the share of comet-like bodies may increase factor of 2

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Öpik-Wetherlill impact probabilities for osculating orbits

2000Planet 4= the moon Number of bodies 58709 H_max= 18.050000 Number of impactors 160 Mean intrinsic probability = = 1.865368E-10 1/Proj <v_imp> 16.122780 <v_inf> 15.916600-------------------------------------Planet 5=Mars Number of bodies 1109

Number of impactors 1109 Mean intrinsic probability = 2.587355E-10 1/Proj <v_imp> 9.929664 <v_inf> 8.330708

2012Planet 4= the moon H.ge. 18. arc_limit 20 Number of bodies 458 Average of impactors 458 Intrinsic probability = 1.58944954E-10 per body <v_imp> 17.0044266 <v_inf> 16.8058947--------------------------------Planet 5=Mars H.ge. 18. arc_limit 20 Number of bodies 5774

Average of impactors 5774 Intrinsic probability = 2.29726429E-10 per body <v_imp> 9.30803356 <v_inf> 7.60588575

2012 astorb.dat, Mars- and Moon-cossers number vs. magnitude(H=18 approximately corresponds to Dproj ~ 1 km

In the current epoch number of Mars-crossers with asteroid like orbits is factor of 20 larger than the number of Moon-crossers. Number of bodies with comet-like orbits is factor of 5 larger for Mars.

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From craters to projectiles

• Scaling laws for impact cratering allow us to convert size-frequency distribution of craters to the size-frequency distribution of projectiles

• Crater-derived curves may be compared with astronomical observations

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Scaling laws for impact cratering 

Coupling parameter:  Transient cavity scaling: (1 + 2) 

Crater collapse: (3)

Ivanov, B., Size-Frequency Distribution of Asteroids and Impact Craters: Estimates of

Impact Rate, in Catastrophic Events Caused by Cosmic Objects, edited by V. V. Adushkin and I. V. Nemchinov, pp. 91-116, Springer,

2008.

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Modeling of impact melt in large terrestrial crater confirm validity of scaling laws for D_crater > 1km

2008 iteration of the scaling law for small (<1-10 km) lunar craters

Blind usage of “standard” scaling laws results in a factor of 6 difference in the R(D_crater) for the same projectile. Looks strange...

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2010-2012 – hydrocode with porosity and dry friction

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+ Demonstration of dry friction importance- Modeling velocity <12 km/c

2012 (Ivanov, LPSC): more realistic dry friction in fragmented rocks with thermal softening under shock/deformational heating

If so (need to be verified more) then1. “Porous target” scaling is wrong

while extrapolated beyond 7 km/s.2. “Shallow” pi_V vs. pi_2 scaling is

mostly due to dry friction, not due to material porosity only.

3. Scaling of “regolith” lunar craters should be redone.

4. How porous is Martian upper layer important for 5-50 m in diameter craters (real impact rate available)???.

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HIRISE modern impact rate

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0.001 0.01 0.1 11E-09

1E-08

R_Daubar

R_4years

RMars_1yr

R_Hart_1yr

R_Hart_10Years

Rmars_10 yr

D (km)

R

The recent data based on the discovery rate based solely on CTX/CTX image comparison (with crater size improved with HiRISE images, 44 impacts) gives factor of 2 to 3 lower cratering rate in the upper diameter bins (Daubar et al, 2012, under revision)“All” craters gives better fit to Hartmann-Neukum chronology

To date around 200 “new” impact cites (impact craters and crater clusters) are found with well bounded formation time

Conclusions

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We are close to update the 2000 Mars/moon cratering rate ratio… but not ready yet.

Pure updating of planetary-crosser’s orbit list of crossers does not change the Mars/moon impact ratio dramatically (despite ~6-fold increase in the number of known objects).

Future discussion should include possible difference in crater-forming projectile properties. Small crater clusters found on Mars witness in favor of the presence of 10% to 20% low density (high porosity?) projectiles.

Two additional questions: (1) the difference in mechanical properties of regolith on the dry Moon and possibly ice-saturated Martian soil, and (2) the efficiency of lunar impacts of low-density objects assumed from Martian strewn fields.

New observational data demands new supportive research and modeling.

Asteroids, Trojan, and JF

comets • Cumulative plot for

Main Belt, Trojan asteroids, and Jupiter Family comets in comparison with cumulative N>D distribution derived for crater forming projectiles (thick curves).

0.1 1 10 100 1000D , km

N(>

D)

Tro jans

1

10

100

103

104

105

106

107

M ain belt

JF com ets

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Asteroids, Trojan, and JF comets (2)

• R-plot for Main Belt asteroids according to Davis et al. (1994) and Spacewatch data by Jedicke and Metcalfe (1998) for all the Main Belt and the inner belt in comparison with the SFD for projectiles formed lunar craters. Trojans are after Jewitt et al. (2000), comets - after Tankredy et al. (2000). 0.1 1 10 100 1000

DP

, km

R

10

100

103

104

105

106

107

M ain B elt

T ro jans

Inner M ain Belt

C om ets

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RECENT DATA

• Sloan Digital Sky Survey (SDSS): Ivezic et al, 2001

• LINEAR: Stuart, 2001

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Physical mechanism of „SFD waves:CRITICAL SPECIFIC ENERGY (Love&Ahrens, 96; Melosh&Ryan,97)

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Near-Earth bodies (2)

• The lunar “projectile curve fitted to N(1)=800 in comparison with bolide data. Letters “T” designate the possible range of Tunguska scale projectiles. 1E-4 0.001 0.01 0.1 1 10 100

D , km

0.1

1

10

1E+2

1E+3

1E +4

1E +5

1E+6

1E+7

1E+8

1E+9

1E+10

1E+11

Nsk

y(>D

)

H <15, P=2.42 10-9 ,yr-1

H <18, P=4.31 10-9

,yr-1

Lunar pro jectiles for N (1km )=800

Tunguska, 32<D (m )<64

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Crater size-frequency distribution:cumulative, increment, relative (R)

Incremental

Relative (R-plot)

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Crater size-frequency distribution:cumulative, increment, relative (R)

Cumulative

Relative (R-plot)

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