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Polar hydrogen deposits on the Moon provide evidence that its spin axis has shifted; analysis of the locations of these deposits and of the lunar figure suggests that the shift occurred as a result of changes in the Moon’s moments of inertia caused by a low-density thermal anomaly beneath the Procellarum region. Polar wandering on the Moon Matthew Siegler and co-authors show that the polar hydrogen deposits detected on the Moon by orbital neutron spectroscopy pose something of a mystery: the spatial distribution of hydrogen, which is thought to arise from the presence of water ice, does not match that expected from present-day lunar temperatures. The explanation may lie in the phenomenon known as 'true polar wander', in which a reference point on a solid body rotates with respect to its spin axis. Based on an analysis of polar deposit locations and of the lunar figure, the authors suggest that the shift occurred as a result of changes in the Moon's moment of inertia caused by a low-density thermal anomaly beneath the Procellarum region. Procellarum was most geologically active early in lunar history, which would imply that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. The earliest dynamic and thermal history of the Moon is not well understood. The hydrogen content of deposits near the lunar poles may yield insight into this history, because these deposits (which are probably composed of water ice) survive only if they remain in permanent shadow. If the orientation of the Moon has changed, then the locations of the shadowed regions will also have changed. The polar hydrogen deposits have been mapped by orbiting neutron spectrometers 1 , 2 , 3 , and their observed spatial distribution does not match the expected distribution of water ice inferred from present-day lunar temperatures 4 , 5 . This finding is in contrast to the distribution of volatiles observed in similar thermal environments at Mercury’s poles 6 . Here we show that polar hydrogen preserves evidence that the spin axis of the Moon has shifted: the hydrogen deposits are antipodal and displaced equally from each pole along opposite longitudes. From the direction and magnitude of the inferred reorientation, and from analysis of the moments of inertia of the Moon, we hypothesize that this change in the spin axis, known as true polar wander, was caused by a low-density thermal anomaly beneath the Procellarum region. Radiogenic heating within this region resulted in the bulk of lunar mare volcanism 7 , 8 , 9 , 10 , 11 and altered the density structure of the Moon, changing its moments of inertia. This resulted in true polar wander consistent with the observed remnant polar hydrogen. This thermal anomaly still exists and, in part, controls the current orientation of the Moon. The Procellarum region was most geologically active early in lunar history 7 , 8 , 9 , which implies that polar wander initiated billions of years ago and that a large portion of the measured polar hydrogen is ancient, recording early delivery of water to the inner Solar System. Our hypothesis provides an explanation for the antipodal distribution of lunar polar hydrogen, and connects polar volatiles to the geologic and geophysical evolution of the Moon and the bombardment history of the early Solar System.

\"This book is the first to document in depth the history of lunar and planetary cartography in Russia. The first map of the far side of the Moon was made with the participation of Lomonosov Moscow University (Sternberg Astronimcal Institute, MSU) in 1960. The developed mapping technologies were then used in preparing the \"Complete map of the Moon\" in 1967 as well as other maps and globes. Over the years, various maps of Mars have emerged from the special course \"Mapping of extraterrestrial objects\" in the MSU Geography Department, including the hypsometric map of Mars at a scale of 1:26,000,000, compiled by J.A. Ilykhina and published in 2004 in an edition of 5,000 copies. A more detailed version of this map has since been produced with a new hypsometric scale. In addition, maps of the northern and southern hemisphers of Mars have been compiled for the hypsometric globe of Mars. Relief maps of Venus were made in 2008, 2010, and 2011, and hypsometric maps of Phobos and Deimos at a scale of 1:60,000 were published in 2011.\" -- Back cover.

The much larger appearance of the moon near horizon than the perceived size of the moon at zenith has motivated many scientists to develop theories that aim at explaining this puzzling phenomenon. Considering that the size of retinal images of the moon in these positions are very similar, the explanation of difference in their apparent sizes has relied on perceptual cues of distance embedded in the retinal image of their respective contexts. Although this account of the moon illusion is quite popular, it does not explain all aspects of this phenomenon. The theoretical formulation of the moon illusion based on other factors such as size contrast later may have had some advantages but has also created some new problems. Although the moon is perceived in a three-dimensional (3D) environment, the present analysis proposes that an explanation of the moon illusion based on two-dimensional (2D) cues can remove some of the unnecessary problems. The empty space and size contrast that have already been considered in explaining classic geometric-optical illusions play a parallel role in explaining the moon illusion. In other words, the role of open space in interaction with the image of the moon and different objects near horizon, all reflected on the retina, are considered as the main explaining factors. The advantages of this approach will be discussed and some of the facts pertaining to the moon illusion will be explained within this theoretical framework.

New analyses undermine a popular theory about an intense asteroid storm 4 billion years ago. New analyses undermine a popular theory about an intense asteroid storm 4 billion years ago.

Impact craters serve as recorders of lunar evolutionary history, and determining the stratigraphic ages of craters is crucial. However, the age of many craters on the Moon remains undetermined. The morphology of craters is closely related to their stratigraphic ages. In the study, we systematically and quantitatively analyzed seven morphological parameters of 432 impact craters with known stratigraphic ages (Copernican, Eratosthenian, Imbrian), including crater depth, wall width, wall height, rim height, irregularity, volume, and roughness, as well as rock abundance. The study provided a range of morphological parameters for craters from the Copernican, Eratosthenian, and Imbrian. Additionally, we derived power law relationships between five morphological parameters and crater diameter, excluding irregularity and roughness. Furthermore, the transitional crater diameters from simple to complex crater morphology were determined for the Copernican and Eratosthenian, approximately 13 km and 15 km, respectively. These results suggest systematic differences in the lunar regolith in different stratigraphic ages. For impact craters of the same diameter, as crater age increases, irregularity tends to be greater, while crater depth, wall width, wall height, rim height, volume, roughness, and rock abundance tend to be smaller. Therefore, in cases where the diameter is determined, the actual values of morphological parameters and rock abundance can be used to constrain the stratigraphic age information of craters of an unknown age.

Geological and geodetic observations of the Moon from spacecraft revealed that it expanded by a few km for the first several hundred million years and then contracted later. The period when the planet expanded most coincides with that when the mare volcanism of the Moon was active. Given the high initial temperature of the deep mantle inferred from the giant impact and mantle overturn hypotheses of the Moon, the observed early expansion is difficult to account for by thermal expansion only. To understand the observed radial change of the Moon, we numerically calculated the thermal evolution of a one-dimensional spherically symmetric mantle caused by transport of heat, mass, and incompatible heat-producing elements (HPEs) by migration of magma that is generated by internal heating. The mantle is assumed to be enriched in HPEs at its base in the initial condition. The calculated mantle expands for the first several hundred million years by melting of the deep mantle and upward migration of the generated magma to the uppermost mantle; the top of the partially molten region rises to the depth level of around 300 km, which is shallow enough to generate mare basalts of the Moon. The migrating magma, however, extracts HPEs from the deep interior, and the planet then contracts gradually by cooling and solidification of the partially molten mantle. We obtained a thermal history model that is consistent with the observed history of radial change of the Moon when the initial mid-mantle temperature TM≈1600K and the initial ratio of the concentration of HPEs in the crust to that of the mantle Fcrst∗≤12. This model suggests that melting of the deep mantle and upward migration of the generated magma strongly affect the thermal history of the Moon. The model we developed here is a good starting point for constructing more realistic models of the thermal history of the Moon where the effects of heat and mass transport by mantle convection are also considered.

The Japanese eel, Anguilla japonica, spawns within the North Equatorial Current that bifurcates into both northward and southward flows in its westward region, so its spawning location and larval transport dynamics seem important for understanding fluctuations in its recruitment to East Asia. Intensive research efforts determined that Japanese eels spawn along the western side of the West Mariana Ridge during new moon periods, where all oceanic life history stages have been collected, including eggs and spawning adults. However, how the eels decide where to form spawning aggregations is unknown because spawning appears to have occurred at various latitudes. A salinity front formed from tropical rainfall was hypothesized to determine the latitude of its spawning locations, but an exact spawning site was only found once by collecting eggs in May 2009. This study reports on the collections of Japanese eel eggs and preleptocephali during three new moon periods in June 2011 and May and June 2012 at locations indicating that the distribution of lower salinity surface water or salinity fronts influence the latitude of spawning sites along the ridge. A distinct salinity front may concentrate spawning south of the front on the western side of the seamount ridge. It was also suggested that eels may spawn at various latitudes within low-salinity water when the salinity fronts appeared unclear. Eel eggs were distributed within the 150-180 m layer near the top of the thermocline, indicating shallow spawning depths. Using these landmarks for latitude (salinity front), longitude (seamount ridge), and depth (top of the thermocline) to guide the formation of spawning aggregations could facilitate finding mates and help synchronize their spawning.

IDEFIX, the Martian Moons eXploration (MMX) mission Phobos rover, will be the first of its kind to attempt wheeled-locomotion on a low-gravity surface. The IDEFIX WheelCams, two cameras placed on the underside of the rover looking at the rover wheels, provide a unique opportunity to study the surface properties of Phobos, regolith behaviour on small-bodies and rover mobility in low-gravity. The information gained about Phobos’ surface will be of high importance to the landing and sampling operations of the main MMX spacecraft, in addition to being valuable for understanding the surface processes and geological history of Phobos. Here we introduce the WheelCam science objectives, the instrument and the characterisation activities. We also discuss the on-going preparations linked to the analysis and interpretation of the WheelCam images on the surface of Phobos.