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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2012

N(50) Crater Retention Ages for an Expanded Inventory of Lunar Basins: Evidence for an Early Heavy Bombardment and a Late Heavy Bombardment?

LOLA topography and LOLA-derived crustal thickness data provide evidence for a population of impact basins on the Moon that is likely a factor 2 larger than the classical lists based on photogeology. Frey (2012) determined N(50) crater retention ages (CRAs) for 83 candidate basins > 300 km in diameter by counting LOLA-identified craters superimposed over the whole area of the basins. For some basins identified in topography or model crustal thickness it is not possible to unambiguously identify the crater rim as is traditionally done. Also, Quasi-Circular Depressions (QCDs) > 50 km in diameter are recognizable in the mare-filled centers of many basins. Even though these are not apparent in image data, they likely represent buried impact craters superimposed on the basin floor prior to mare infilling and so should be counted in determining the age of the basin. Including these as well as the entire area of the basins improves the statistics, though the error bars are still large when using only craters > 50 km in diameter. The distribution of N(50) CRAs had two distinct peaks which did not depend on whether the basins were named (based on photogeology) or recognized first in topography or crustal thickness data. It also did not depend on basin diameters (both larger and smaller basins made up both peaks) and both peaks persisted even when weaker candidates were excluded. Burgess (2012, unpublished data) redid the counts for 85 basins but improved on the earlier effort by adjusting the counting area where basins overlap. The two peak distribution of N(50) ages was confirmed, with a younger peak at N(50) ~ 40-50 and an older peak at N(50) ~ 80-90 (craters > 50 km diameter per million square km). We suggest this could represent two distinct populations of impactors on the Moon: one producing an Early Heavy Bombardment (EHB) that predates Nectaris and the second responsible for the more widely recognized Late Heavy Bombardment (LHB).

Frey, Herbert↗
NASA NTRS2002

A New Dynamical Model for the Lunar Late Heavy Bombardment

We describe a new dynamical model for the late heavy bombardment in which a 5th terrestrial planet existed on an orbit that became unstable after 600 Myr, began crossing the asteroid belt, and enhanced the flux of impactors into the inner Solar System. Additional information is contained in the original extended abstract.

Chambers, J. E.↗
NASA NTRS2015

Evidence Supporting an Early as Well as Late Heavy Bombardment on the Moon

Evidence supporting an intense early bombardment on the Moon in addition to the traditional Late Heavy Bombardment at approx. 4 BY ago include the distribution of N(50) Crater Retention Ages (CRAs) for candidate basins, a variety of absolute age scenarios for both a "young" and an "old" Nectaris age, and the decreasing contrasts in both topographic relief and Bouguer gravity with increasing CRA.

Moon↗
NASA NTRS2012

Mega-Impacts on Mars: Implications for the Late Heavy Bombardment in the Inner Solar System, and the Early Evolution of the Earth and Mars

There are about 30 very large impact basins on Mars, > 1000 km in diameter, most of which are revealed by their topographic and/or crustal thickness signatures. Crater retention ages and model absolute ages suggest these all formed in a relatively short time (100-200 million years?), perhaps during a "Late Heavy Bombardment" (LHB) caused by the evolution of the orbits of the giant planets. This so-called "Nice Model" of planetary formation may explain the LHB on the Moon at about 3.9 billion years ago and would have produced a similar bombardment throughout the inner solar system. The formation of 30 very large impact basins would have had catastrophic environmental consequences for Mars, which were further complicated by the demise of the global magnetic field at about the same time. If there are no very large basins on Mars older than the 30 we see and the LHB really lasted everywhere only a short time, there may have been a relatively longer time (~400 million years?) during which Mars and the Earth suffered no major impact trauma and during which conditions on both worlds may have been far more habitable than during the LHB. However, if the formation of the Mars crustal dichotomy was due to an even larger giant impact that predated the very large basins, all record of this earlier and possibly more clement time on Mars may have been erased. Ages of the smaller but still very large basins can be used to approximately date the giant impact (if it occurred). Even the very large basins appear to have reset the crater retention ages of the entire crust of Mars and may have by themselves erased any record of an earlier time.

Frey, Herbert↗
NASA NTRS2012

Stratigraphy, Sequence, and Crater Populations of Lunar Impact Basins from Lunar Orbiter Laser Altimeter (LOLA) Data: Implications for the Late Heavy Bombardment

New measurements of the topography of the Moon from the Lunar Orbiter Laser Altimeter (LOLA)[1] provide an excellent base-map for analyzing the large crater population (D.20 km)of the lunar surface [2, 3]. We have recently used this data to calculate crater size-frequency distributions (CSFD) for 30 lunar impact basins, which have implications for their stratigraphy and sequence. These data provide an avenue for assessing the timing of the transitions between distinct crater populations characteristic of ancient and young lunar terrains, which has been linked to the late heavy bombardment (LHB). We also use LOLA data to re-examine relative stratigraphic relationships between key lunar basins.

Fassett, C. I.↗
NASA NTRS2011

Spitzer Evidence for a Late Heavy Bombardment and the Formation of Urelites in {eta}Corvi at Approximately 1 Gyr

We have analyzed Spitzer and NASA/IRTF 2 - 35 micrometer spectra of the warm, ~350 K circumstellar dust around the nearby MS star eta Corvi (F2V, 1.4 plus or minus 0.3 Gyr). The spectra show clear evidence for warm, water- and carbon-rich dust at ~3 AU from the central star, in the system's Terrestrial Habitability Zone. Spectral features due to ultra-primitive cometary material were found, in addition to features due to impact produced silica and high temperature carbonaceous phases. At least 9 x 10(exp 18) kg of 0.1 - 100 micrometer warm dust is present in a collisional equilibrium distribution with dn/da ~ a(exp -3.5), the equivalent of a 130 km radius KBO of 1.0 grams per cubic centimeter density and similar to recent estimates of the mass delivered to the Earth at 0.6 - 0.8 Gyr during the Late Heavy Bombardment. We conclude that the parent body was a Kuiper-Belt body or bodies which captured a large amount of early primitive material in the first Myrs of the system's lifetime and preserved it in deep freeze at approximately 150 AU. At approximately 1.4 Gyr they were prompted by dynamical stirring of their parent Kuiper Belt into spiraling into the inner system, eventually colliding at 5-10 kilometers per second with a rocky planetary body of mass less than or equal to M(sub Earth at approximately 3 AU, delivering large amounts of water (greater than 0.1 % of M(sub Earth's Oceans)) and carbon-rich material. The Spitzer spectrum also closely matches spectra reported for the Ureilite meteorites of the Sudan Almahata Sitta fall in 2008, suggesting that one of the Ureilite parent bodies was a KBO.

Lisse, C. M.↗
NASA NTRS2002

Dynamics of Possible Late Heavy Bombardment Impactor Populations

The existence of the later lunar basins implies the existence of a massive dynamical reservoir that can store small bodies for some 6000 Myr after the Moon formed. We will discuss four recent models for such reservoirs. Additional information is contained in the original extended abstract.

Dones, Luke↗
NASA NTRS1991

Glacial and marine chronology of Mars

A hydrological model involving episodic oceans and ice sheets on Mars has been presented by Baker, et al. One of the main uncertainties concerning this model is the age and correlation of these events. Even more uncertain are their absolute ages. However, based on stratigraphic and cratering evidence, the most recent occurrence of these events was relatively late in Martian history. The cratering record on Mars can be divided into three general periods: (1) the period of late heavy bombardment; (2) a transition period at the end of late heavy bombardment; and (3) the post heavy bombardment era. The crater size/frequency distribution represented by the period of late heavy bombardment is characterized by a complex curve with a differential-2 slope (cumulative-1) at diameters less than about 50 km diameter, while the post heavy bombardment size distribution has a differential-3 slope (cumulative-2) over the same diameter range. An R plot is presented of the size/freqency distribution of ejecta blanket craters on the Argyre esker plains and similar craters in Hellas. The relative chronology is summarized of oceans, ice sheets, and other major events in Martian history.

Strom, Robert G.↗
NASA NTRS2012

Using GRIDVIEW to Better Understand the Early Bombardment History of the Moon, Mars and Earth

For more than a decade we have used GRIDVIEW to help analyze topographic and related data for Mars and more recently for the Moon. Our focus has been to employ the stretching, contouring, profiling, circle-fitting and other capabilities of GRIDVIEW to search for Quasi-Circular Depressions (CTAs) in MOLA, LOLA and other topographic data, and for Circular Thin Areas (CTAs) in Mars and Moon model crustal thickness data. Both QCDs and CTAs likely represent buried or obscured impact craters not readily visible in image data. We found clear evidence for a much larger population of buried impact craters in the northern lowlands of Mars (Frey et al. 2002), suggesting that part of the Red Planet is not significantly younger than the southern highlands. Edgar and Frey (2008) found that the N(300) crater retention ages of both areas were essentially identical, a conclusion confirmed by Wyatt (unpublished data) using more recent crustal thickness data for Mars. MOLA topographic data and MOLA-derived crustal thickness data were used to both identify a large number of previously unrecognized very large impact basins (D> 1000 km) on Mars and to determine relative crater retention ages for them (Frey, 2008). The distribution of N(300) CRAs suggested most formed in a relatively short interval of time. This dating also suggested the main magnetic field of Mars disappeared during this period (Lillis et al., 2008), because only the youngest basins systematically lack a remagnetized signature. Similar QCD and CTA analysis of first Clementine (Frey, 2011) and more recently LOLA topographic and LOLA-derived crustal thickness data for the Moon (Frey et al., 2011) revealed a significantly larger population of impact basins > 300 km in diameter than previously known. N(50) CRAs suggest a two-peak distribution of ages (Frey, 2012). An improved counting process confirms the two peaks, perhaps indicating both a pre-Nectaris Early Heavy Bombardment (EHB) as well as a Late Heavy Bombardment (LHB) on the Moon (Frey and Burgess, 2012, this meeting), with obvious implications for the early bombardment history of the Earth.

Frey, Herbert↗
NASA NTRS1981

Crater populations on Ganymede and Callisto

Voyager 1 observations reveal heavily cratered surfaces on Ganymede and Callisto which suggest that a period of heavy bombardment occurred in the outer solar system. The overall crater density on Ganymede indicates that the oldest regions began recording the observed crater population at a later time than Callisto. A diameter-dependent loss of craters from 10-40 km occurs on Ganymede and may be due to ice formation or the formation of arcuate troughs. Evidence is given which suggests that the population of bodies responsible for the period of late heavy bombardment in the inner solar system is very different from that responsible for the late heavy bombardment in the outer solar system. In addition, it is postulated that Ganymede and Callisto may principally record a population of bodies that never penetrated the inner solar system in numbers great enough to leave a recognizable signature.

Strom, R. G.↗
NASA NTRS1978

Emergence of the continents

If early degassing of the Earth produced a global ocean several km deep overlying a global sialic crust, then late heavy bombardment of that crust by basin forming impacting bodies would have produced topography such that by 4 billion years ago dry continential landmasses would stand above sea level. From extrapolation of lunar crater statistics, at least 50% of an original global crust on the earth would have been converted into basins averaging 4 km deep after isostatic adjustment. These basins formed the sink into which such a global ocean would drain. If the ocean was initially 2 km deep, then approximately 50% of the early Earth would have stood above sea level when the late heavy bombardment came to a close.

Frey, H.↗
NASA NTRS1981

Limits on large-crater production and obliteration on Callisto

By comparing results of Monte Carlo simulations of the crater population on Callisto with the observed surface, it is demonstrated that the relative dearth of large craters on Ganymede and Callisto, compared with the terrestrial planets, can not be totally ascribed either to craters relaxing or to craters piercing a thin icy crust. Consequently, the population of objects responsible for the heavy bombardment of the Jovian system differed markedly from that responsible for the late heavy bombardment of the terrestrial planets.

Woronow, A.↗
NASA NTRS1975

Comparative studies of lunar, Martian, and Mercurian craters and plains

The spatial distribution of lunar smooth plains is not consistent with experimental simulations of melt rock emplacement during cratering in layered materials. Nor is it consistent with the location of melt rocks (suevite) near the Ries basin. Lunar smooth plains surrounding Imbrium are most extensive in areas where pre-existing craters are most degraded. This observation suggests that plains form by impact of basin and local primary crater ejecta, together with deposition of debris excavated by the resultant secondary cratering events. Craters within the belt of smooth plains surrounding the Caloris basin on Mercury are most degraded nearest the basin; this suggests that Mercurian smooth plains must, at least in part, be emplaced in a manner similar to plains surrounding the Imbrium basin. Mercurian uplands have a primary crater population deficient in small crater diameters (less than approximately 30 km). Lunar uplands far from major basins also have a crater population deficient in small crater sizes. Martian cratered terrain exhibits a similar crater deficiency, which was previously interpreted as due to obliteration of small craters (less than approximately 30 km) by some surface process. A crater size distribution deficient in small sizes (less than approximately 30 km) on the Mercurian, lunar, and Martian uplands has implications for the origin of debris bombarding the inner solar system during the period recorded by these surfaces. It is proposed that during late heavy bombardment, the inner solar system was inundated with bodies that broke up under tidal fission as they approached the planets. Such a mechanism would lend to production of a crater population deficient in small crater sizes, and it would also explain the large degree of spatial clustering of primary craters on Mercury, the moon, and Mars.

Oberbeck, V. R.↗
NASA NTRS1992

Asteroids and Archaean crustal evolution: Tests of possible genetic links between major mantle/crust melting events and clustered extraterrestrial bombardments

Since the oldest intact terrestrial rocks of ca. 4.0 Ga and oldest zircon xenocrysts of ca. 4.3 Ga measured to date overlap with the lunar late heavy bombardment, the early Precambrian record requires close reexamination vis a vis the effects of megaimpacts. The identification of microtektite-bearing horizons containing spinals of chondritic chemistry and Ir anomalies in 3.5-3.4-Ga greenstone belts provides the first direct evidence for large-scale Archaean impacts. The Archaean crustal record contains evidence for several major greenstone-granite-forming episodes where deep upwelling and adiabatic fusion of the mantle was accompanied by contemporaneous crustal anatexis. Isotopic age studies suggest evidence for principal age clusters about 3.5, 3.0, and 2.7 (+/- 0.8) Ga, relics of a ca. 3.8-Ga event, and several less well defined episodes. These peak events were accompanied and followed by protracted thermal fluctuations in intracrustal high-grade metamorphic zones. Interpretations of these events in terms of internal dynamics of the Earth are difficult to reconcile with the thermal behavior of silicate rheologies in a continuously convecting mantle regime. A triggering of these episodes by mantle rebound response to intermittent extraterrestrial asteroid impacts is supported by (1) identification of major Archaean impacts from microtektite and distal ejecta horizons marked by Ir anomalies; (2) geochemical and experimental evidence for mantle upwelling, possibly from levels as deep as the transition zone; and (3) catastrophic adiabatic melting required to generate peridotitic komatites. Episodic differentiation/accretion growth of sial consequent on these events is capable of resolving the volume problem that arises from comparisons between modern continental crust and the estimated sial produced by continuous two-stage mantle melting processes. The volume problem is exacerbated by projected high accretion rates under Archaean geotherms. It is suggested that impact shock effects have been largely obscured by (1) outpouring of voluminous basic/ultrabasic lavas, inundating shock-deformed crust and extending beyond the perimeters of impact excavated basins; (2) gravity subsidence and downfaulting of terrestrial maria, accounting for the burial and anatexis of subgreenstone basement; and (3) extensive shearing and recrystallization at elevated temperatures of impact structure, breccias, and mineral deformation features beneath impact-excavated basins, relics of which may be retained in structural windows in high-grade metamorphic terranes.

Glikson, A. Y.↗
NASA NTRS2018

Constraining Solar System Bombardment Using In Situ Radiometric Dating

The leading, but contentious, model for lunar impact history includes a pronounced increase in impact events at around 3.9 Ga. This late heavy bombardment would have scarred Mars and the terrestrial planets, influenced the course of biologic evolution on the early Earth, and rearranged the very architecture of our Solar System. But what if it's not true? In the last decade, new observations and sample analyses have reinterpreted basin ages and "pulled the pin" on the cataclysm - we may only have the age of one large basin (Imbrium). The Curie mission would constrain the onset of the cataclysm by determining the age of a major pre-Imbrium lunar basin (Nectaris or Crisium), characterize new lunar lithologies far from the Apollo and Luna landing sites, including the basalts in the basin-filling maria and olivine-rich lithologies in the basin margins, and provide a unique vantage point to assess volatiles in the lunar regolith from dawn to dusk.

Cohen, Barbara A.↗
NASA NTRS2016

Dating Howardite Melt Clasts: Evidence for an Extended Vestan Bombardment?

Howardites are polymict breccias that, together with eucrites and diogenites (HED), likely originate from the vestan surface (regolith/ megaregolith), and display a heterogeneous distribution of eucritic and diogenitic material. Melt clasts are also present alongside other regolithic features within howardites, and are noteworthy for their compositional variability and appearance. Melt clasts formed by impact events provide a snapshot of the timings and conditions of surface gardening and bombardment on the vestan surface. By dating such clasts, we aim to better constrain the timings of impact events on Vesta, and to establish whether the impact flux in the asteroid belt was similar to that on the Moon. As the Moon is used as the basis for characterising impact models of the inner solar system, it is necessary to verify that apparent wide-scale events are seen in other planetary bodies. In particular, the observed clustering of Apollo melt clast ages between 3.8-4.0 Ga has led to two hypotheses: 1) The Moon was subjected to a sudden event - 'Lunar Cataclysm' or period of 'Late Heavy Bombardment' (LHB), 2) The age cluster represents the end of an epoch of declining bombardment or 'Heavy Bombardment. No consensus has emerged regarding one or other hypothesis. We are testing these hypotheses by seeking evidence for such events in materials other than those derived from the Moon.

Cartwright, J. A.↗