About age of the lunar surface

Planetary Science Inst Report, 1987

Reviews in Mineralogy and Geochemistry

Planetary and Space Science, 2017

Analysing the size-frequency distribution of very small lunar craters (sized below 100 m including ones below 10 m) using LROC images, spatial density and related age estimations were calculated for mare and terra terrains. Altogether 1.55 km 2 area was surveyed composed of 0.1-0.2 km 2 units, counting 2784 craters. The maximal areal density was present at the 4-8 m diameter range at every analysed terrain suggesting the bombardment is areally relatively homogeneous. Analysing the similarities and differences between various areas, the mare terrains look about two times older than the terra terrains using <100 m diameter craters. The calculated ages ranged between 13 and 20 Ma for mare, 4-6 Ma for terra terrains. Substantial fluctuation (min: 936 craters/km 2 , max: 2495 craters/km 2) was observed without obvious source of nearby secondaries or fresh ejecta blanket produced fresh crater. Randomness analysis and visual inspection also suggested no secondary craters or ejecta blanket from fresh impact could contribute substantially in the observed heterogeneity of the areal distribution of small cratersthus distant secondaries or even other, poorly known resurfacing processes should be considered in the future. The difference between the terra/mare ages might come only partly from the easier identification of small craters on smooth mare terrains, as the differences were observed for larger (30-60 m diameter) craters too. Difference in the target hardness could more contribute in this effect. It was possible to separate two groups of small craters based on their appearance: a rimmed thus less eroded, and a rimless thus more eroded one. As the separate usage of different morphology groups of craters for age estimation at the same area is not justifiable, this was used only for comparison. The SFD curves of these two groups showed characteristic differences: the steepness of the fresh craters' SFD curves are similar to each other and were larger than the isochrones. The eroded craters' SFD curves also resemble to each other, which are less steep than the isochrones. These observations confirm the expectation that as the time passes by, rims are erased and depressions became shallower, presenting such observations for the first time in this small crater size range.

Icarus, 2013

Standard lunar chronologies, based on combining lunar sample radiometric ages with impact crater densities of inferred associated units, have lately been questioned about the robustness of their interpretations of the temporal dependance of the lunar impact flux. In particular, there has been increasing focus on the ''middle age'' of lunar bombardment, from the end of the Late Heavy Bombardment ($3.8 Ga) until comparatively recent times ($1 Ga). To gain a better understanding of impact flux in this time period, we determined and analyzed the cratering ages of selected terrains on the Moon. We required distinct terrains with random locations and areas large enough to achieve good statistics for the small, superposed crater size-frequency distributions to be compiled. Therefore, we selected 40 lunar craters with diameter $90 km and determined the model ages of their floors by measuring the density of superposed craters using the Lunar Reconnaissance Orbiter Wide Angle Camera mosaic. Absolute model ages were computed using the Model Production Function of Marchi et al. (Marchi, S., Mottola, S., Cremonese, G., Massironi, M., Martellato, E. [2009]. Astron. J. 137,[4936][4937][4938][4939][4940][4941][4942][4943][4944][4945][4946][4947][4948]. We find that a majority (36 of 40) of our superposed crater size-frequency distributions are consistent with the Model Production Function. A histogram of the original crater floor model ages indicates the bombardment rate decreased gradually from $3.8 Ga until $3.0 Ga, implying an extended tail to the Late Heavy Bombardment. For large craters, it also preliminarily suggests that between $3.0 and 1.0 Ga bombardment may be characterized by long periods (>600 Myr) of relatively few impacts (''lulls'') broken by a short duration ($200 Myr) of relatively more impacts (''spike''). While measuring superposed craters, we also noted if they were part of a cluster or chain (named ''obvious secondary''), and analyzed these craters separately. Interestingly, we observe a wide variety of slopes to the differential size-frequency power-law, which demonstrates that there can be considerable variation in individual secondary crater field size-frequency distributions. Finally, four of the small, superposed crater size-frequency distributions are found to be inconsistent with the Model Production Function; possible reasons are: resurfacing has modified these distributions, unrecognized secondary craters, and/or the Model Production Function has incorrect inputs (such as the scaling law for the target terrain). The degraded appearance of the superposed craters and indications of resurfacing suggest that the first cause is the most likely.

Space Sciences Series of ISSI, 2001

The well investigated size-frequency distributions (SFD) for lunar craters is used to estimate the SFD for projectiles which formed craters on terrestrial planets and on asteroids. The result shows the relative stability of these distributions during the past 4 Gyr. The derived projectile size-frequency distribution is found to be very close to the size-frequency distribution of Main-Belt asteroids as compared with the recent Spacewatch asteroid data and astronomical observations (Palomar-Leiden survey, IRAS data) as well as data from close-up imagery by space missions. It means that asteroids (or, more generally, collisionally evolved bodies) are the main component of the impactor family. Lunar crater chronology models of the authors published elsewhere are reviewed and refined by making use of refinements in the interpretation of radiometric ages and the improved lunar SFD. In this way, a unified cratering chronology model is established which can be used as a safe basis for modeling the impact chronology of other terrestrial planets, especially Mars.

Advances in Space Research, 1982

Impact cratering as a geologic process on the terrestrial planets is addressed. The crater densities on the Earth and Moon form the basis for a standard flux-time curve, which can be used to date unsampled planetary surfaces and constrain the temporal history of endogenic geologic processes. The attached uncertainties and the shape of the flux curve (a rapid exponential decay for the period 14.6 -'4.0 by, followed by the establishment of a constant flux by 3.5 -3.0 by which continues more or less to the present) are such that only very old C~3 8 by) and very young (~1 0 by) surfaces can be dated with some confidence Dating of intermediate-aged surfaces is more imprecise, a problem which is most significant for the geologic history of Mars.

Highlights of Astronomy, 1977

Analysis of cratering on all terrestrial planets and satellites has produced tools to study (1) the past meteoroid and planetesimal environment, (2) the erosive environments of planetary surfaces, and (3) the relative and absolute ages of planetary surface units. Important findings Q include a decline in lunar crater production rate from a value 4 x 1 0 years ago that was thousands of times higher than the present,. to present values which have been relatively constant for 2 to 3 x 10 years; evidence for an erosive period or periods on Mars that degraded many Martian craters but declined substantially at some time in the past; and the concept of destruction of primeval planetary surfaces by early intense cratering and production of a mega-regolith. All seven planets and satellites in the inner solar system are known to have craters. Craters on Mercury, moon, Mars, Phobos and Deimos were revealed by spacecraft or telescopic imagery; those on Venus by radar; and those on earth are still being discovered by geologic exploration. Several arguments indicate that the majority of the multi-kilometer craters can be ascribed to impacts of asteroid-like bodies. Among these are patterns of ejecta and secondary pits; required energies surpassing known volcanic eruptions; and matches between observed size distribution of craters and asteroids (one being converted to the other by means of empirical relations between crater diameter and necessary energy). The craters allow a number of practical applications to the study of the planets, illustrated and reviewed informally by Hartmann (1977a)The conversion between crater sizes and sizes of original planetesimals allows study of the planetesimal environment. Such studies on lightly-cratered plains of different planets reveal that the multikilometer craters are distributed with similar, size distributions that can be approximated by power laws of form N=kD , where N is the number of craters of size greater than diameter D. The constant b is the slope in commonly-used N-log D plots. Least squares fit of the author's crater counts, for example, give B = 1.96 for craters from 2 to 128 km diameter oh both lunar frontside maria and Martian Tharsis volcanic plains (Hartmann, 1977b).

Earth, Moon, and Planets, 2021

We present a study on the relationship between the ratio of the depth of a crater to its diameter and the diameter for lunar craters both on the maria and on the highlands. We consider craters younger than 1.1 billion years in age, i.e. of Copernican period. The aim of this work is to improve our understanding of such relationships based on our new estimates of the craters's depth and diameter. Previous studies considered similar relationships for much older craters (up to 3.2 billion years). We calculated the depths of craters with diameters from 10 to 100 km based on the altitude profiles derived from data obtained by the Lunar Orbiter Laser Altimeter (LOLA) onboard the Lunar Reconnaissance Orbiter (LRO). The obtained ratios h/D of the depths h of the craters to their diameters D can differ by up to a factor of two for craters with almost the same values of diameters. The linear and power approximations (regressions) of the dependence of h/D on D were made for simple and complex Copernican craters selected from the data from Mazrouei et al. (Science 363:253-255, 2019) and Losiak et al. (Lunar Impact Crater Database, 2015). For the separation of highland craters into two groups based only on their dependences of h/D on D, at D < 18 km these are mostly simple craters, although some complex craters can have diameters D ≥ 16 km. Depths of mare craters with D ≤ 14 km are greater than 0.15D. Following Pike's (Lunar Planet Sci XII:845-847, 1981) classification, we group mare craters of D < 15 km as simple craters. Mare craters with 15 < D < 18 km fit both approximation curves for simple and complex craters. Depths of mare craters with D > 18 km are in a better agreement with the approximation curve of h/D versus D for complex craters than for simple craters. At the same diameter, mare craters are deeper than highland craters at a diameter smaller than 30-40 km. For greater diameters, highland craters are deeper. The values of h/D for our approximation curves are mainly smaller than the values of the curve by Pike (in: Roddy, Pepin, Merrill (eds) Impact and explosion cratering: planetary and terrestrial implications, University of Arizona Press, Tucson, 1977) at D < 15 km. Only for mare craters at D < 11 km, our approximation curve is a little higher than the curve by Pike (1977). For our power approximations, the values of h/D obtained for complex craters are greater than those obtained by Pike (1981) at D > 53 km for highland craters, and at D < 80 km for mare craters.

Geophysical Research Letters, 1991

Using a simple model of lunar topographic evolution resulting from the formation of impact craters, we try to constrain the total number of impactors striking the Moon after the solidification of the lunar crust. The numerical results indicate that the evolution of the Moon's hypsometric curve is strongly influenced by the total number of craters and is less affected by their size distribution. It is suggested that the total number of craters necessary to explain the standard deviation of the present hypsomettic curve is roughly equivalent to the number density of craters on the oldest lunar crust, corresponding to about 10-4 lunar mass of impactors. This may be the total mass of impactors striking after solidification of the lunar crust, more specifically, after about 4.4 to 4.5 Ga ago when the viscous degradation of craters became ineffective.

2016

In this experiment the shadow length of a crater wall and the Sun's zenith angle at the time of observation were used to calculate the depth of craters on the moon. We then calculated the impact energy of an asteroid to cause such craters. Finally we used these details to calculate an approximate range of the mass of asteroids hitting the moon. We also calculated an estimate for the total number of asteroids to hit the moon.