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Timing, Abundance, and Spatial Extent of Initial Magmatism on the Moon Explained By Cumulate Mantle Overturn

We have recently quantified the timing, abundance, and spatial extent of lower mantle melting induced by cumulate overturn on the Moon through a series of 3D geodynamical models. Our dynamical modeling indicates that overturn of thin (~30-50 km) and weak ilmenite-bearing cumulates (IBC) triggers a rapid, short-lived, and widespread period of lower mantle melting which reproduces the key geochronological, volume, and spatial characteristics associated with the onset of secondary magmatism on the Moon (Figs. 1,2), and without energy contributions from KREEP (potassium, rare earth elements, phosphorus, radiogenic U, Th). Within the guiding paradigms of global differentiation via magma ocean crystallization and subsequent cumulate mantle overturn, our model provides explanation for near contemporaneous primary and secondary crust production constrained by geochronology of returned lunar samples and meteorites. In this abstract, we discuss our results in context with several intricacies of lunar chronology including models of a long-lived magma ocean, the hypothesis that mantle overturn was induced by the giant South Pole-Aitken basin forming impact, and ancient lunar zircon.

T. C. Prissel↗
NASA NTRS1989

Mineralogical and chemical properties of the lunar regolith

The composition of lunar regolith and its attendant properties are discussed. Tables are provided listing lunar minerals, the abundance of plagioclase feldspar, pyroxene, olivine, and ilmenite in lunar materials, typical compositions of common lunar minerals, and cumulative grain-size distribution for a large number of lunar soils. Also provided are charts on the chemistry of breccias, the chemistry of lunar glass, and the comparative chemistry of surface soils for the Apollo sites. Lunar agglutinates, constructional particles made of lithic, mineral, and glass fragments welded together by a glassy matrix containing extremely fine-grained metallic iron and formed by micrometeoric impacts at the lunar surface, are discussed. Crystalline, igneous rock fragments, breccias, and lunar glass are examined. Volatiles implanted in lunar materials and regolith maturity are also addressed.

Mckay, David S.↗
NASA NTRS2004

The Net Carbon Flux due to Deforestation and Forest Re-Growth in the Brazilian Amazon: Analysis using a Process-Based Model

We developed a process-based model of forest growth, carbon cycling, and land cover dynamics named CARLUC (for CARbon and Land Use Change) to estimate the size of terrestrial carbon pools in terra firme (non-flooded) forests across the Brazilian Legal Amazon and the net flux of carbon resulting from forest disturbance and forest recovery from disturbance. Our goal in building the model was to construct a relatively simple ecosystem model that would respond to soil and climatic heterogeneity that allows us to study of the impact of Amazonian deforestation, selective logging, and accidental fire on the global carbon cycle. This paper focuses on the net flux caused by deforestation and forest re-growth over the period from 1970-1998. We calculate that the net flux to the atmosphere during this period reached a maximum of approx. 0.35 PgC/yr (1PgC = 1 x 10(exp I5) gC) in 1990, with a cumulative release of approx. 7 PgC from 1970- 1998. The net flux is higher than predicted by an earlier study by a total of 1 PgC over the period 1989-1 998 mainly because CARLUC predicts relatively high mature forest carbon storage compared to the datasets used in the earlier study. Incorporating the dynamics of litter and soil carbon pools into the model increases the cumulative net flux by approx. 1 PgC from 1970-1998, while different assumptions about land cover dynamics only caused small changes. The uncertainty of the net flux, calculated with a Monte-Carlo approach, is roughly 35% of the mean value (1 SD).

Hirsch, A. I.↗
NASA NTRS1999

An Assessment of the Impact of the 1997-98 El Nino on the Asian-Australian Monsoon

Using state-of-the-art satellite-gauge monthly rainfall estimate and optimally interpolated sea surface temperature (SST) data, we have assessed the 1997-98 AA-monsoon anomalies in terms of three basic causal factors: basin-scale SST, regional coupling, and internal variability. Singular Value Decomposition analyses of rainfall and SST are carried out globally over the entire tropics and regionally over the AA-monsoon domain. Contributions to monsoon rainfall predictability by various factors are evaluated from cumulative anomaly correlation with dominant regional SVD modes. Results reveal a dominant, large-scale monsoon-El Nino coupled mode with well-defined centers of action in the near-equatorial monsoon regions during the boreal summer and winter respectively. The observed 1997-98 AA-monsoon anomalies are found to be very complex with approximately 34% of the anomalies of the Asian (boreal) summer monsoon and 74% of the Australia (austral) monsoon attributable to basin-scale SST influence associated with El Nino. Regional coupled processes contribute an additional 19% and 10%, leaving about 47% and 16% due to internal dynamics for the boreal and austral monsoon respectively. For the boreal summer monsoon, it is noted that the highest monsoon predictability is not necessary associated with major El Nino events (e.g. 1997, 1982) but rather in non-El Nino years (e.g. 1980, 1988) when contributions from the regional coupled modes far exceed those from the basin-scale SST. The results suggest that in order to improve monsoon seasonal-to-interannual predictability, there is a need to exploit not only monsoon-El Nino relationship, but also intrinsic monsoon regional coupled processes.

Lau, K.-M.↗
NASA NTRS1992

Mesosiderite clasts with the most extreme positive europium anomalies among solar system rocks

Pigeonite-plagioclase gabbros that occur as clasts in mesosiderites (brecciated stony-iron meteorites) show extreme fractionations of the rare-earth elements (REEs) with larger positive europium anomalies than any previously known for igneous rocks from the earth, moon, or meteorite parent bodies and greater depletions of light REEs relative to heavy REEs than known for comparable cumulate gabbros. The REE pattern for merrillite in one of these clasts is depleted in light REEs and has a large positive europium anomaly as a result of metamorphic equilibration with the silicates. The extreme REE ratios exhibited by the mesosiderite clasts demonstrate that multistage igneous processes must have occurred on some asteroids in the early solar system. Melting of the crust by large-scale impacts or electrical induction from an early T-Tauri-phase sun may be responsible for these processes.

Mittlefehldt, David W.↗
NASA NTRS1983

Impact cratering and spall failure at gabbro

Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the - 9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80%) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m)of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejectra resides in a few large fragments.

Lange, M. A.↗
NASA NTRS2005

Relative Ages of the Highlands, Lowlands, and Transition Zone Along a Portion of the Mars Crustal Dichotomy from Densities of Visible and Buried Impact Craters

Understanding the fundamental age relationships of the different parts of the Mars Crustal Dichotomy is essential to fully understanding the events that shaped the early history and formation of the surface of Mars. A dominant question is what are the true relative ages of the Northern Lowlands and the Southern Highlands? Using MOLA data from the Mars Global Surveyor and Viking visual images, a dataset of both buried and visible crater diameters was created over a nine million sq km study area of a section of the dichotomy boundary stretching from Arabia Terra to Utopia Planitia. Cumulative frequency plots on a log-log scale were used to determine the relative ages for the Highlands, the Lowlands, and the Transition Zone, separately for the visible, the buried and the combined total (visible+ buried) populations. We find the overall Highland crater population in this area is slightly older than the Lowlands, consistent with previous global studies, but the Lowlands and Transition Zone are also very old and formed at roughly the same time. It appears that the formation of the Lowlands in this region formed contemporaneously with a large-scale resurfacing event in the Highlands, perhaps caused by the process responsible for the Lowland formation.

DeSoto, G. E.↗
NASA NTRS1984

Impact cratering and spall failure of gabbro

Both hypervelocity impact and dynamic spall experiments were carried out on a series of well-indurated samples of gabbro. The impact experiments carried out with 0.04 to 0.2 g, 5-6 km/sec projectiles produced deci-centimeter-sized craters and demonstrated crater efficiencies of 6/10 to the -9 g/erg, and order of magnitude greater than in metal and some two to three times that of previous experiments on less strong igneous rocks. Most of the crater volume (some 60 to 80 percent) is due to spall failure. Distribution of cumulative fragment number, as a function of mass of fragments with masses greater than 0.1 gram yield values of b = d(log10N sub f)dlog10(m) of -0.5 to -0.6, where N sub f is the cumulate number of fragments and m is the mass of fragments. These values are in agreement or slightly higher than those obtained for less strong rocks and indicate that a large fraction of the ejecta resides in a few large fragments.

Lange, M. A.↗
NASA NTRS1973

On the improper neglect of certain terms in random function theory

This paper presents some exact solutions of problems in random function theory for the purpose of testing the validity of an approximate method known variously in the many different fields of its application as first order smoothing theory, first order cumulant discard, quasilinear theory, or the adiabatic approximation. The hydromagnetic dynamo equations are used here, as particularly appropriate for such an investigation. The calculations show that in one case the exact and approximate solutions agree. In the other case the approximate solution is wrong. Hence, in the absence of a general criterion for validity, a result based on first order smoothing theory is a conjecture rather than a fact. This impacts strongly on much of the recent work on hydromagnetic dynamos.

Lerche, I.↗
NASA NTRS2002

Probabilistic Study of Fluid Structure Interaction

A combustor liner was computationally simulated and probabilistically evaluated in view of the several uncertainties in the aerodynamic, structural, material and thermal variables that govern the combustor liner. The interconnection between the computational fluid dynamics code and the finite element structural analysis codes was necessary to couple the thermal profiles with structural design. The stresses and their variations were evaluated at critical points on the liner. Cumulative distribution functions and sensitivity factors were computed for stress responses due to the aerodynamic, mechanical and thermal random variables. It was observed that the inlet and exit temperatures have a lot of influence on the hoop stress. For prescribed values of inlet and exit temperatures, the Reynolds number of the flow, coefficient of thermal expansion, gas emissivity and absorptivity and thermal conductivity of the material have about the same impact on the hoop stress. These results can be used to quickly identify the most critical design variables in order to optimize the design and make it cost effective.

Gorla, Rama S. R.↗
NASA NTRS1999

Environmental Conditions and Threatened and Endangered Species Populations near the Titain, Atlas, and Delta Launch Complexes, Cape Canaveral Air Station

Launches of Delta, Atlas, and Titan rockets from Cape Canaveral Air Station (CCAS) have potential environmental effects. These could occur from direct impacts of launches or indirectly from habitat alterations. This report summarizes a three-year study (1995-1998) characterizing the environment, with particular attention to threatened and endangered species, near Delta, Atlas, and Titan launch facilities. Cape Canaveral has been modified by Air Force development and by 50 years of fire suppression. The dominant vegetation type around the Delta and Atlas launch complexes is coastal oak hammock forest. Oak scrub is the predominant upland vegetation type near the Titan launch complexes. Compositionally, these are coastal scrub communities that has been unburned for greater than 40 years and have developed into closed canopy, low-stature forests. Herbaceous vegetation around active and inactive facilities, coastal strand and dune vegetation near the Atlantic Ocean, and exotic vegetation in disturbed areas are common. Marsh and estuarine vegetation is most common west of the Titan complexes. Launch effects to vegetation include scorch, acid, and particulate deposition. Discernable, cumulative effects are limited to small areas near the launch complexes. Water quality samples were collected at the Titan, Atlas, and Delta launch complexes in September 1995 (wet season) and January 1996 (dry season). Samples were analyzed for heavy metals, chloride, total organic carbon, calcium, iron, magnesium, sodium, total alkalinity, pH, and conductivity. Differences between fresh, brackish, and saline surface waters were evident. The natural buffering capacity of the environment surrounding the CCAS launch complexes is adequate for neutralizing acid deposition in rainfall and launch deposition. Populations of the Florida Scrub-Jay (Aphelocoma coerulescens), a Federally- listed, threatened species, reside near the launch complexes. Thirty-seven to forty-one scrub-jay territories were located at Titan, Atlas, and Delta launch complexes between 1995 and 1997. No direct impacts to scrub-jays were observed as a result of normal launches. The explosion of the Delta rocket in January 1997 caused direct impacts to the habitat of several scrub-jays families, from fire and debris; however, no scrub-jay mortality was observed. Mortality exceeded reproductive output at all areas over the course of the study. Populations of the southeastern beach mouse (Peromyscus polionotus niveiventris) populations, a Federally listed, threatened species, reside near all the launch complexes. Hurricane Erin and several other tropical storms impacted several areas at the inception of the study in 1995 causing coastal habitat alterations as a result of salt-water intrusion. Both the habitat and the beach mice populations recovered during the course of the study. No direct impacts to southeastern beach mice were observed as a result of normal launch operations. Direct impacts were observed to the habitat as a result of the explosion of the Delta rocket in January 1997. This alteration of the habitant resulted in a shift in use with the mice moving on to the newly burned part of the site. Waterbirds use wetlands and aquatic systems near the launch complexes. Species include the Federally-listed, endangered Wood Stork (Mycteria americana) and several state-listed species of special concern including the Snowy Egret (Egretta thula thula), Reddish Egret (Egretta rufescens rufescens), White Ibis (Eudocimus albus), Roseate Spoonbill (Ajaia ajaja), Tricolored Heron (Egretta tricolor ruficolis), and Little Blue Heron (Egretta caerulea). No impacts to these populations resulting from any launch operations were observed. Gopher tortoises (Gopherus polyphemus) also occur around the launch complexes. Most of those observed appeared to be in good condition; however, upper respiratory tract disease is known to occur in the population. Cape Canaveral Air Station, including areas near active launch complexes, remains important habitat for a variety of native plants and animals including threatened and endangered species. Direct negative effects of current launch systems appear limited. Additional monitoring of these populations and habitats is required to determine if subtle, long-term changes are occurring, to determine if new launch systems and facilities cause other effects, and to determine the effects of habitat restoration and management.

Oddy, Donna M.↗
NASA NTRS1999

Environmental Conditions and Threatened and Endangered Species Populations near the Titan, Atlas, and Delta Launch Complexes, Cape Canaveral Air Station

Launches of Delta, Atlas, and Titan rockets from Cape Canaveral Air Station (CCAS) have potential environmental effects. These could occur from direct impacts of launches or indirectly from habitat alterations. This report summarizes a three-year study (1 995-1 998) characterizing the environment, with particular attention to threatened and endangered species, near Delta, Atlas, and Titan launch facilities. Cape Canaveral has been modified by Air Force development and by 50 years of fire suppression. The dominant vegetation type around the Delta and Atlas launch complexes is coastal oak hammock forest. Oak scrub is the predominant upland vegetation type near the Titan launch complexes. Compositionally, these are coastal scrub communities that has been unburned for > 40 years and have developed into closed canopy, low-stature forests. Herbaceous vegetation around active and inactive facilities, coastal strand and dune vegetation near the Atlantic Ocean, and exotic vegetation in disturbed areas are common. Marsh and estuarine vegetation is most common west of the Titan complexes. Launch effects to vegetation include scorch, acid, and particulate deposition. Discernable, cumulative effects are limited to small areas near the launch complexes. Water quality samples were collected at the Titan, Atlas, and Delta launch complexes in September 1995 (wet season) and January 1996 (dry season). Samples were analyzed for heavy metals, chloride, total organic carbon, calcium, iron, magnesium, sodium, total alkalinity, pH, and conductivity. Differences between fresh, brackish, and saline surface waters were evident. The natural buffering capacity of the environment surrounding the CCAS launch complexes is adequate for neutralizing acid deposition in rainfall and launch deposition. Populations of the Florida Scrub-Jay (Aphelocoma coerulescens), a Federally-listed, threatened species, reside near the launch complexes. Thirty-seven to forty-one scrub-jay territories were located at Titan, Atlas, and Delta launch complexes between 1995 and 1997. No direct impacts to scrub-jays were observed as a result of normal launches. The explosion of the Delta rocket in January 1997 caused direct impacts to the habitat of several scrub-jays families, from fire and debris; however, no scrub-jay mortality was observed. Mortality exceeded reproductive output at all areas over the course of the study. Populations of the southeastern beach mouse (Peromyscus polionotus niveiventris) populations, a Federally listed, threatened species, reside near all the launch complexes. Hurricane Erin and several other tropical storms impacted several areas at the inception of the study in 1995 causing coastal habitat alterations as a result of salt-water intrusion. Both the habitat and the beach mice populations recovered during the course of the study. No direct impacts to southeastern beach mice were observed as a result of normal launch operations. Direct impacts were observed to the habitat as a result of the explosion of the Delta rocket in January 1997. This alteration of the habitat resulted in a shift in use with the mice moving on to the newly burned part of the site. Waterbirds use wetlands and aquatic systems near the launch complexes. Species include the Federally-listed, endangered Wood Stork (Mycferia americana) and several state-listed species of special concern including the Snowy Egret (Egretfa thula fhula), Reddish Egret (Egreffa rufescens rufescens), White Ibis (Eudocimus albus), Roseate Spoonbill (Ajaia ajaja), Tricolored Heron (Egreffa tricolor ruficolis), and Little Blue Heron (Egreffa caerulea). No impacts to these populations resulting from any launch operations were observed. Gopher tortoises (Gopherus polyphemus) also occur around the launch complexes. Most of those observed appeared to be in good condition; however, upper respiratory tract disease is known to occur in the population. Cape Canaveral Air Station, including areas near active launch colexes, remains important habitat for a variety of native plants and animals including threatened and endangered species. Direct negative effects of current launch systems appear limited. Additional monitoring of these populations and habitats is required to determine if subtle, long-term changes are occurring, to determine if new launch systems and facilities cause other effects, and to determine the effects of habitat restoration and management.

Oddy, Donna M.↗
NASA NTRS1984

Apollo 16 - Impact melt sheets, contrasting nature of the Cayley plains and Descartes mountains, and geologic history

Apollo 16 stations four and five rake samples have been examined petrographically and by electron microprobe and INAA. Lithologic abundances support the idea (Korontev, 1981) that the variation of soil composition at Apollo 16 results from mixing between a component represented by station five and components much like either the dimict breccias or feldspathic fragmental breccias in composition. Pyroxene, olivine, and coexisting plagioclase compositions from within the anorthosite portions of dimict breccias bridge the gap between the Mg-rich and ferroan anorthosite fields. Analyses from associated cumulate and granulitic clasts indicate that they are the source of the intermediate material. Dimict breccias formed about 3.92 b.y. ago, the nectaris event occurred 3.84-3.92 b.y. ago, and the Cayley plains were deposited as a result of the Imbrium event sometime later than 3.84 b.y.

Mckinley, J. P.↗
NASA NTRS1977

Comparison of lunar rocks and meteorites: Implications to histories of the moon and parent meteorite bodies

There are many similarities between lunar samples and stone meteorites. Lunar samples, especially from the highlands, indicate that they have been affected by complex and repeated impact processes. Similar complex and repeated impact processes have also been operative on the achondritic and chondritic meteorites. Similarities between lunar and meteoritic rocks are discussed as follows: (1) Monomict and polymict breccias occur in lunar rocks, as well as in achondritic and chondritic meteorites, having resulted from complex and repeated impact processes; (2) Chondrules are present in lunar meteorites, as well as in a few achondritic and most chondritic meteorites. They apparently crystallized spontaneously from molten highly supercooled droplets which may have formed from impact melts or, perhaps, volcanic processes (as well as from the solar nebula, in the case of meteoritic chondrites); (3) Lithic fragments vary from little modified (relative to the apparent original texture) to partly or completely melted and recrystallized lithic fragments. Their detailed study allows conclusions to be drawn about their parent rock types and their origin, thereby gaining insight into preimpact histories of lunar and meteoritic breccias. There is evidence that cumulate rocks were involved in the early history of both moon and parent meteorite bodies.

Prinz, M.↗
NASA NTRS2024

Assessing the Relationships Between Sensorimotor Biomarkers and Post-Landing Functional Task Performance

Spaceflight drives adaptive changes in healthy individuals appropriate for sensorimotor function in a microgravity environment. These changes are maladaptive for return to earth's gravity. The inter-individual variability of sensorimotor decrements is striking, although poorly understood. The goal of this study is to identify a set of behavioral, neuroimaging and genetic measures that can be used to predict early post-flight performance on a set of sensorimotor tasks. Astronauts are recruited who previously participated in sensorimotor field tests and/or posturography soon after long-duration spaceflight. Behavioral tests include assessments of sensory dependency and adaptability. Visual dependency involves treadmill walking while viewing a moving virtual visual scene. Vestibular perceptual thresholds are measured while seated during lateral translations. Proprioception dependency is measured during one-legged stance on a horizontal air-bearing surface. Ground assessment of adaptability is performed(1) during treadmill walking with a virtual linear hallway and a moving walking surface, and (2) during multiple trials of navigating an obstacle course while wearing reversing prisms(adaptive Functional Mobility Test, aFMT). The neuroimaging tests will characterize individual differences in regional brain volumes (using Structural MRI) and white matter microstructure(using Diffusion Tensor Imaging) to serve as potential predictors of adaptive capacity. The genetic tests will utilize saliva samples to examine variations in four genes chosen because of their ability to differentiate sensorimotor adaptation ability in a normative population, including Catechol-O-methyltransferase (COMT), Dopamine Receptor D2 (DRD2), Brain-derived neurotrophic factor (BDNF) and the α2-adrenergic receptor. Twenty-seven ISS crewmembers have been tested to date, including 6 from this past year. This cohort includes 10first-time fliers, 6F, and mission durations lasting 178.6 ± 30.5 days, mean ± std. We are utilizing a combination of three post-flight functional task outcomes: tandem walk, recovery from fall and dynamic posturography. There is considerable variability among the post-flight performance outcomes for the 27participants to date. Based on a partial sample using an ordinal scale survey, 70% indicated their ability to perform functional tasks were more impacted postflight relative to inflight with 50% indicating they needed to restrict movements for a longer period postflight relative to inflight. While there is a strong association within tests obtained at different R+0 timepoints, by R+24 hr performance on one post-flight test does not necessarily correlate with performance on other post-flight tests. There are apparent relationships between individual measures and specific post-flight outcome measures, e.g., the cumulative time to complete the aFMT is significantly correlated to pre-to-post-flight changes in tandem walk (rho= 0.64, p = 0.001). Preliminary statistical analysis indicates combining biomarkers will increase predictive power and this will be explored with future analyses. Our preliminary findings underscore the importance of a comprehensive post-flight test battery including different types of tasks with varying sensory feedback. We expect that understanding the relationships between these sensorimotor biomarkers and post-flight functional task performance will improve both our understanding of the individual variability and our strategy to optimize sensorimotor countermeasures

S J Wood↗
NASA NTRS1979

Results of the examination of the Skylab/Apollo windows for micrometeroid impacts

Examination of the Command Module windows of the Skylab/Apollo 3 and 4 spacecraft at 5x magnification resulted in the detection of 18 micrometeroid craters 80 microns and larger in diameter for an accumulated exposure time of 144 days. A 20x magnification examination of the windows of the Skylab/Apollo 4 spacecraft identified 6 such craters between 20 and 70 microns in diameter for 84 days exposure. As the Skylab was oriented such that its solar panels faced the sun continuously, the three windows examined had a fixed orientation also. The six small craters were all found on the window that faced in the solar direction. A cumulative flux per square centimeter per year is given for pit and spall diameters.

Cour-Palais, B. G.↗
NASA NTRS1979

Large impact basins on Mercury and relative crater production rates

A search for impact basins on Mercury having diameters greater than 200 km revealed evidence for 40 such structures on the 47% of Mercury mapped at sufficient resolution by Mariner 10. This is similar to the number (35) found by Schaber et al. (1977), although there is disagreement in the details of both diameters (for basins observed by them and by the authors) and in the existence of individual basins. The differences are described in detail. A log (cumulative number/unit area)-log (diameter) plot for mercurian basins has a least squares slope of -2; basins show somewhat less scatter about this line than do the Schaber et al. basins. Mercury has (in cumulative number/unit area) only 37% as many basins as does the moon over the entire range of diameters greater than 300 km. If both the moon and Mercury have had similar preservation times for craters and if common populations of impactors are involved, then Mars-crossers may have been a dominant contribution to the basin-forming objects.

Frey, H.↗
NASA NTRS2006

Cosmic Ray Mantle Visibility on Kuiper Belt Objects

Optically red objects constitute the dynamically cold, old component of the Classical Kuiper Belt (40 - 47 AU) with heliocentric orbits of low eccentricity and inclination. The red colors likely arise from primordial mixed ices processed by irradiation to meters in surface depth over the past four billion years, since the time of giant planet migration and Kuiper Belt stirring, at relatively moderate dosages of 60 gigarads provided by galactic cosmic ray protons and heavier ions. The red cosmic ray mantle is uniformly visible on the cold classical objects beneath a minimally thin eroded layer of more neutrally colored material arising from cumulative effects of heliospheric particle irradiation. The radiation fluxes are lowest in the middle heliospheric region containing the Classical Kuiper Belt and increase from there both towards and away from the Sun. Despite increasing irradiation at various times of solar system history from increases in solar and interstellar ion fluxes, the red object region has apparently never reached sufficiently high dosage levels to neutralize in color the red mantle material. Erosion processes, including plasma sputtering and micrometeroid impacts, act continuously to reduce thickness of the upper neutral crust and expose the cosmic ray mantle. A deeper layer at tens of meters and more may consist of relatively unprocessed ices that can erupt to the surface by larger impacts or cryovolcanism and account for brighter surfaces of larger objects such as 2003 UB313. Surface colors among the Kuiper Belt and other icy objects of the outer solar system are then a function, assuming uniform primordial composition, of relative thickness for the three layers and of the resurfacing age dependent on the orbital and impact history of each object.

Cooper, John F.↗