Analytical Model for the Tidal Evolution of the Evection Resonance and the Timing of Resonance Escape
ABSTRACT: A high-angular momentum giant impact with the Earth can produce a Moon with a silicate isotopic composition nearly identical to that of Earth’s mantle, consistent with observations of terrestrial and lunar rocks. However, such an event requires subsequent angular momentum removal for consistency with the current Earth-Moon system. The early Moon may have been captured into the evection resonance, occurring when the lunar perigee precession period equals 1 year. It has been proposed that after a high- angular momentum giant impact, evection removed the angular momentum excess from the Earth-Moon pair and transferred it to Earth’s orbit about the Sun. However, prior N-body integrations suggest this result depends on the tidal model and chosen tidal parameters. Here, we examine the Moon’s encounter with evection using a complementary analytic description and the Mignard tidal model. While the Moon is in resonance, the lunar longitude of perigee librates, and if tidal evolution excites the libration amplitude sufficiently, escape from resonance occurs. The angular momentum drain produced by formal evection depends on how long the resonance is maintained. We estimate that resonant escape occurs early, leading to only a small reduction (~ few to 10%) in the Earth-Moon system angular momentum. Moon formation from a high-angular momentum impact would then require other angular momentum removal mechanisms beyond standard libration in evection, as have been suggested previously. Plain Language Summary A canonical giant impact with the Earth by a Mars-sized impactor can produce the Moon and the current Earth-Moon angular momentum. However, such an impact would produce a planet and protolunar disk with very different proportions of impactor-derived material, likely leading to Earth-Moon compositional differences that are inconsistent with observed Earth-Moon isotopic similarities. Alternatively, a high-angular momentum impact could form a disk with a silicate composition similar to that of the Earth, but with a postimpact angular momentum much higher than in the current Earth-Moon system. As the early Moon tidally receded from the Earth, its perigee precession period lengthened. When this period equaled 1 year, the Moon may have been captured into the evection resonance with the Sun. It has been proposed that evection removed the angular momentum excess from the Earth- Moon pair, but the appropriate degree of angular momentum removal appears sensitive to tidal models. In this work, we use an analytical model to examine the Moon’s evolution in evection and find that escape from formal resonance occurs early, with limited angular momentum reduction. Thus, in order for a high-angular momentum giant impact to be consistent with the current Earth-Moon system, additional mechanisms that do not involve standard resonance occupancy appear required.
Project description:In the giant impact theory, the Moon formed from debris ejected into an Earth-orbiting disk by the collision of a large planet with the early Earth. Prior impact simulations predict that much of the disk material originates from the colliding planet. However, Earth and the Moon have essentially identical oxygen isotope compositions. This has been a challenge for the impact theory, because the impactor's composition would have likely differed from that of Earth. We simulated impacts involving larger impactors than previously considered. We show that these can produce a disk with the same composition as the planet's mantle, consistent with Earth-Moon compositional similarities. Such impacts require subsequent removal of angular momentum from the Earth-Moon system through a resonance with the Sun as recently proposed.
Project description:The position of the Moon in relation to the Earth and the Sun gives rise to several predictable cycles, and natural changes in nighttime light intensity are known to cause alterations to physiological processes and behaviors in many animals. The limited research undertaken to date on the physiological responses of animals to the lunar illumination has exclusively focused on the synodic lunar cycle (full moon to full moon, or moon phase) but the moon's orbit-its distance from the Earth-may also be relevant. Every month, the moon moves from apogee, its most distant point from Earth-and then to perigee, its closest point to Earth. Here, we studied wild barnacle geese (Branta leucopsis) to investigate the influence of multiple interacting lunar cycles on the physiology of diurnally active animals. Our study, which uses biologging technology to continually monitor body temperature and heart rate for an entire annual cycle, asks whether there is evidence for a physiological response to natural cycles in lunar brightness in wild birds, particularly "supermoon" phenomena, where perigee coincides with a full moon. There was a three-way interaction between lunar phase, lunar distance, and cloud cover as predictors of nighttime mean body temperature, such that body temperature was highest on clear nights when the full moon coincided with perigee moon. Our study is the first to report the physiological responses of wild birds to "supermoon" events; the wild geese responded to the combination of two independent lunar cycles, by significantly increasing their body temperature at night. That wild birds respond to natural fluctuations in nighttime ambient light levels support the documented responses of many species to anthropogenic sources of artificial light, that birds seem unable to override. As most biological systems are arguably organized foremost by light, this suggests that any interactions between lunar cycles and local weather conditions could have significant impacts on the energy budgets of birds.
Project description: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 ?17O. 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 ?17O 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.
Project description:Using viscoelastic mass spring model simulations to track heat distribution inside a tidally perturbed body, we measure the near/far side asymmetry of heating in the crust of a spin synchronous Moon in eccentric orbit about the Earth. With the young Moon within. 8 Earth radii of the Earth, we find that tidal heating per unit area in a lunar crustal shell is asymmetric due to the octupole order moment in the Earth's tidal field and is 10 to 20% higher on its near side than on its far side. Tidal heating reduces the crustal basal heat flux and the rate of magma ocean crystallization. Assuming that the local crustal growth rate depends on the local basal heat flux and the distribution of tidal heating in latitude and longitude, a heat conductivity model illustrates that a moderately asymmetric and growing lunar crust could maintain its near/far side thickness asymmetry but only while the Moon is near the Earth.
Project description:A giant impact onto Earth led to the formation of the Moon, resulted in a lunar magma ocean (LMO), and initiated the last event of core segregation on Earth. However, the timing and temporal link of these events remain uncertain. Here, we demonstrate that the low thermal conductivity of the lunar crust combined with heat extraction by partial melting of deep cumulates undergoing convection results in an LMO solidification time scale of 150 to 200 million years. Combining this result with a crystallization model of the LMO and with the ages and isotopic compositions of lunar samples indicates that the Moon formed 4.425 ± 0.025 billion years ago. This age is in remarkable agreement with the U-Pb age of Earth, demonstrating that the U-Pb age dates the final segregation of Earth's core.
Project description:The distribution and isotopic composition of volatile elements in planetary materials holds a key to the characterization of the early solar system and the Moon's formation. The Moon and Earth are chemically and isotopically very similar. However, the Moon is highly depleted in volatile elements and the origin of this depletion is still debated. We present gallium isotopic and elemental measurements in a large set of lunar samples to constrain the origin of this volatile depletion. We show that while Ga has a geochemical behavior different from zinc, both elements show a systematic enrichment in the heavier isotopes in lunar mare basalts and Mg-suite rocks compared to the silicate Earth, pointing to a global-scale depletion event. On the other hand, the ferroan anorthosites are isotopically heterogeneous, suggesting a secondary distribution of Ga at the surface of the Moon by volatilization and condensation. The isotopic difference of Ga between Earth and the Moon and the isotopic heterogeneity of the crustal ferroan anorthosites suggest that the volatile depletion occurred following the giant impact and during the lunar magma ocean phase. These results point toward a Moon that has lost its volatile elements during a whole-scale evaporation event and that is now relatively dry compared to Earth.
Project description:The Moon bears a striking compositional and isotopic resemblance to the bulk silicate Earth (BSE) for many elements, but is considered highly depleted in many volatile elements compared to BSE due to high-temperature volatile loss from Moon-forming materials in the Moon-forming giant impact and/or due to evaporative loss during subsequent magmatism on the Moon. Here, we use high-pressure metal-silicate partitioning experiments to show that the observed low concentrations of volatile elements sulfur (S), selenium (Se), tellurium (Te), and antimony (Sb) in the silicate Moon can instead reflect core-mantle equilibration in a largely to fully molten Moon. When incorporating the core as a reservoir for these elements, their bulk Moon concentrations are similar to those in the present-day bulk silicate Earth. This suggests that Moon formation was not accompanied by major loss of S, Se, Te, Sb from Moon-forming materials, consistent with recent indications from lunar carbon and S isotopic compositions of primitive lunar materials. This is in marked contrast with the losses of other volatile elements (e.g., K, Zn) during the Moon-forming event. This discrepancy may be related to distinctly different cosmochemical behavior of S, Se, Te and Sb within the proto-lunar disk, which is as of yet virtually unconstrained.
Project description:The abundance of volatile elements and compounds, such as zinc, potassium, chlorine, and water, provide key evidence for how Earth and the Moon formed and evolved. Currently, evidence exists for a Moon depleted in volatile elements, as well as reservoirs within the Moon with volatile abundances like Earth's depleted upper mantle. Volatile depletion is consistent with catastrophic formation, such as a giant impact, whereas a Moon with Earth-like volatile abundances suggests preservation of these volatiles, or addition through late accretion. We show, using the "Rusty Rock" impact melt breccia, 66095, that volatile enrichment on the lunar surface occurred through vapor condensation. Isotopically light Zn (?66Zn = -13.7‰), heavy Cl (?37Cl = +15‰), and high U/Pb supports the origin of condensates from a volatile-poor internal source formed during thermomagmatic evolution of the Moon, with long-term depletion in incompatible Cl and Pb, and lesser depletion of more-compatible Zn. Leaching experiments on mare basalt 14053 demonstrate that isotopically light Zn condensates also occur on some mare basalts after their crystallization, confirming a volatile-depleted lunar interior source with homogeneous ?66Zn ? +1.4‰. Our results show that much of the lunar interior must be significantly depleted in volatile elements and compounds and that volatile-rich rocks on the lunar surface formed through vapor condensation. Volatiles detected by remote sensing on the surface of the Moon likely have a partially condensate origin from its interior.
Project description:The lunar semidiurnal influence is already known for tidal rivers. The moon also influences inland rivers at a monthly scale through precipitation. We show that, for some non-tidal rivers, with special geological conditions, the lunar semidiurnal tidal oscillation can be detected. The moon has semidiurnal tidal influence on groundwater, which will then export it to streamflow. Long time series with high frequency measurements were analysed by using standard wavelet analysis techniques. The lunar semidiurnal signal explains the daily double-peaked river level evolution of inland gauges. It is stronger where springs with high discharge occur, especially in the area of Edwards-Trinity and Great Artesian Basin aquifers and in areas with dolomite/limestone strata. The average maximum semidiurnal peaks range between 0.002 and 0.1 m. This secondary effect of the earth tides has important implications in predicting high resolution hydrographs, in the water cycle of wetlands and in water management.
Project description:The Moon may have formed from an Earth-orbiting disk of vapor and melt produced by a giant impact.1 The Moon and Earth's mantles have similar compositions. However, it is unclear why lunar samples are more depleted in volatile elements than terrestrial mantle rocks2-3, given that an evaporative escape mechanism4 appears inconsistent with expected disk conditions.5 Dynamical models6-7 suggest that the Moon initially accreted from the outermost disk, but later acquired up to 60% of its mass from melt originating from the inner disk. Here we combine dynamical, thermal and chemical models to show that volatile depletion in the Moon can be explained by preferential accretion of volatile-rich melt in the inner disk to the Earth, rather than to the growing Moon. Melt in the inner disk is initially hot and volatile-poor, but volatiles condense as the disk cools. In our simulations, the delivery of inner disk melt to the Moon effectively ceases when gravitational interactions cause the Moon's orbit to expand away from the disk, and this termination of lunar accretion occurs prior to condensation of potassium and more volatile elements. Thus, the portion of the Moon derived from the inner disk is expected to be volatile depleted. We suggest that this mechanism may explain part or all of the Moon's volatile depletion, depending on the degree of mixing within the lunar interior.