Forming the Moon from terrestrial silicate-rich material

Recent high-precision measurements of the isotopic composition of lunar rocks demonstrate that the bulk silicate Earth and the Moon show an unexpectedly high degree of similarity. This is inconsistent with one of the primary results of classic dynamical simulations of the widely accepted giant impact model for the formation of the Moon, namely that most of the mass of the Moon originates from the impactor, not Earth. Resolution of this discrepancy without changing the main premises of the giant impact model requires total isotopic homogenisation of Earth and impactor material after the impact for a wide range of elements including O, Si, K, Ti, Nd and W. Even if this process could explain the O isotope similarity, it is unlikely to work for the much heavier, refractory elements. Given the increasing uncertainty surrounding the giant impact model in light of these geochemical data, alternative hypotheses for lunar formation should be explored. In this paper, we revisit the hypothesis that the Moon was formed directly from terrestrial mantle material. We show that the dynamics of this scenario requires a large amount of energy, almost instantaneously generated additional energy. The only known source for this additional energy is nuclear fission. We show that it is feasible to form the Moon through the ejection of terrestrial silicate material triggered by a nuclear explosion at Earths core-mantle boundary (CMB), causing a shock wave propagating through the Earth. Hydrodynamic modelling of this scenario shows that a shock wave created by rapidly expanding plasma resulting from the explosion disrupts and expels overlying mantle and crust material.Comment: 26 pages, 5 figures, 1 tabl

Earth-like Habitats in Planetary Systems

Understanding the concept of habitability is related to an evolutionary knowledge of the particular planet-in-question. Additional indications so-called "systemic aspects" of the planetary system as a whole governs a particular planet's claim on habitability. Here we focus on such systemic aspects and discuss their relevance to the formation of an 'Earth-like' habitable planet. We summarize our results obtained by lunar sample work and numerical models within the framework of the Research Alliance "Planetary Evolution and Life". We consider various scenarios which simulate the dynamical evolution of the Solar System and discuss the likelihood of forming an Earth-like world orbiting another star. Our model approach is constrained by observations of the modern Solar System and the knowledge of its history. Results suggest that the long-term presence of terrestrial planets is jeopardized due to gravitational interactions if giant planets are present. But habitability of inner rocky planets may be supported in those planetary systems hosting giant planets. Gravitational interactions within a complex multiple-body structure including giant planets may supply terrestrial planets with materials which formed in the colder region of the proto-planetary disk. During these processes, water, the prime requisite for habitability, is delivered to the inner system. This may occur either during the main accretion phase of terrestrial planets or via impacts during a post-accretion bombardment. Results for both processes are summarized and discussed with reference to the lunar crater record. Starting from a scenario involving migration of the giant planets this contribution discusses the delivery of water to Earth, the modification of atmospheres by impacts in a planetary system context and the likelihood of the existence of extrasolar Earth-like habitable worlds.Comment: 36 Pages, 6 figures, 2014, Special Issue in Planetary and Space Science on the Helmholtz Research Alliance on Planetary Evolution and Lif

Evolution of the moon: The 1974 model

The interpretive evolution of the moon can be divided now into seven major stages beginning sometime near the end of the formation of the solar system. These stages and their approximate durations in time are as follows: (1) The Beginning: 4.6 billion years ago, (2) The Melted Shell: 4.6 to 4.4 billion years ago, (3) The Cratered Highlands: 4.4 to 4.1 billion years ago, (4) The Large Basins: 4.1 to 3.9 billion years ago, (5) The Light-colored Plains: 3.9 to 3.8 billion years ago, (6) The Basaltic Maria: 3.8 to 3.0(?) billion years ago, and (7) The Quiet Crust: 3.0(?) billion years ago to the present. The contributions of the Apollo and Luna exploration toward the study of those stages of evolution are reviewed

Geoscience and a Lunar Base: A Comprehensive Plan for Lunar Exploration

This document represents the proceedings of the Workshop on Geoscience from a Lunar Base. It describes a comprehensive plan for the geologic exploration of the Moon. The document begins by explaining the scientific importance of studying the Moon and outlines the many unsolved problems in lunar science. Subsequent chapters detail different, complementary approaches to geologic studies: global surveys, including orbiting spacecraft such as Lunar Observer and installation of a global geophysical network; reconnaissance sample return mission, by either automated rovers or landers, or by piloted forays; detailed field studies, which involve astronauts and teleoperated robotic field geologists. The document then develops a flexible scenario for exploration and sketches the technological developments needed to carry out the exploration scenario

Workshop on Pristine Highlands Rocks and the early History of the Moon

Oxide composition of the Moon, evidence for an initially totally molten Moon, geophysical contraints on lunar composition, random sampling of a layered intrusion, lunar highland rocks, early evolution of the Moon, mineralogy and petrology of the pristine rocks, relationship of the pristine nonmore rocks to the highlands soils and breccias, ferroan anorthositic norite, early lunar igneous history, compositional variation in ferroan anosthosites, a lunar magma ocean, deposits of lunar pristine rocks, lunar and planetary compositions and early fractionation in the solar nebula, Moon composition models, petrogenesis in a Moon with a chondritic refractory lithophile pattern, a terrestrial analog of lunar ilmenite bearing camulates, and the lunar magma ocean are summarized

An outline of planetary geoscience

A philosophy for planetary geoscience is presented to aid in addressing a number of major scientific questions; answers to these questions should constitute the basic geoscientific knowledge of the solar system. However, any compilation of major questions or basic knowledge in planetary geoscience involves compromises and somewhat arbitrary boundaries that reflect the prevalent level of understanding at the time

Evolution of the moon: The 1974 model

Investigations are reported of Apollo and Luna explorations which have brought about the understanding of the moon and its structure. It is shown that with this knowledge of the moon, a better understanding is presented of the earth's origin, structure and composition

Oxygen isotopic evidence for accretion of Earth's water before a high-energy Moon-forming giant impact

The Earth-Moon system likely formed as a result of a collision between two large planetary objects. Debate about their relative masses, the impact energy involved, and the extent of isotopic homogenization continues. We present the results of a high-precision oxygen isotope study of an extensive suite of lunar and terrestrial samples.We demonstrate that lunar rocks and terrestrial basalts show a 3 to 4 ppm (parts per million), statistically resolvable, difference in Δ17O. Taking aubrite meteorites as a candidate impactor material, we show that the giant impact scenario involved nearly complete mixing between the target and impactor. Alternatively, the degree of similarity between the Δ17O values of the impactor and the proto-Earth must have been significantly closer than that between Earth and aubrites. If the Earth-Moon system evolved from an initially highly vaporized and isotopically homogenized state, as indicated by recent dynamical models, then the terrestrial basalt-lunar oxygen isotope difference detected by our study may be a reflection of post–giant impact additions to Earth. On the basis of this assumption, our data indicate that post–giant impact additions to Earth could have contributed between 5 and 30% of Earth’s water, depending on global water estimates. Consequently, our data indicate that the bulk of Earth’s water was accreted before the giant impact and not later, as often proposed

Workshop on Moon in Transition: Apollo 14, KREEP, and Evolved Lunar Rocks

Lunar rocks provide material for analyzing lunar history and now new evaluation procedures are available for discovering new information from the Fra Mauro highlands rocks, which are different from any other lunar samples. These and other topics were discussed at this workshop, including a new evaluation of the nature and history of KREEP, granite, and other evolved lunar rock types, and ultimately a fresh evaluation of the transition of the moon from its early anorthosite-forming period to its later stages of KREEPy, granitic, and mare magmatism. The summary of presentations and discussion is based on notes taken by the respective summarizers during the workshop