Estimates of the amount of water outgassed from Mars, based on the composition of the atmosphere, range from 6 to 160 m, as compared with 3 km for the Earth. In contrast, large flood features, valley networks, and several indicators of ground ice suggest that at least 500 m of water have outgassed. The two sets of estimates may be reconciled if early in its history, Mars lost part of its atmosphere by impact erosion and hydrodynamic escape.

Water on Mars

High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.

/pdf/the-crust-of-the-moon-as-seen-by-grail-1glf8bzv6k.pdf

The Crust of the Moon as Seen by GRAIL

Lunar sourcebook. A user's guide to the moon

Progress in probability density function methods for turbulent reacting flows

The Holy GRAIL? The gravity field of a planet provides a view of its interior and thermal history by revealing areas of different density. GRAIL, a pair of satellites that act as a highly sensitive gravimeter, began mapping the Moon's gravity in early 2012. Three papers highlight some of the results from the primary mission. Zuber et al. (p. 668, published online 6 December) discuss the overall gravity field, which reveals several new tectonic and geologic features of the Moon. Impacts have worked to homogenize the density structure of the Moon's upper crust while fracturing it extensively. Wieczorek et al. (p. 671, published online 6 December) show that the upper crust is 35 to 40 kilometers thick and less dense—and thus more porous—than previously thought. Finally, Andrews-Hanna et al. (p. 675, published online 6 December) show that the crust is cut by widespread magmatic dikes that may reflect a period of expansion early in the Moon's history. The Moon's gravity field shows that the lunar crust is less dense and more porous than was thought. High-resolution gravity data obtained from the dual Gravity Recovery and Interior Laboratory (GRAIL) spacecraft show that the bulk density of the Moon's highlands crust is 2550 kilograms per cubic meter, substantially lower than generally assumed. When combined with remote sensing and sample data, this density implies an average crustal porosity of 12% to depths of at least a few kilometers. Lateral variations in crustal porosity correlate with the largest impact basins, whereas lateral variations in crustal density correlate with crustal composition. The low-bulk crustal density allows construction of a global crustal thickness model that satisfies the Apollo seismic constraints, and with an average crustal thickness between 34 and 43 kilometers, the bulk refractory element composition of the Moon is not required to be enriched with respect to that of Earth.

The crust of the Moon as seen by GRAIL

/pdf/aqueous-alteration-of-nakhlites-implications-for-water-on-4ygmalrgvw.pdf

Aqueous alteration of Nakhlites: implications for water on Mars

Angrites are a small group of silica undersaturated achondrites notable for their apparent lack of shock features or brecciation and their characteristic unusual mineralogy. We are interested in studying their magmatic history, as reflected by their light-element chemistry. Here, we report on the abundance, distribution and isotopic composition of nitrogen in a suite of 5 angrites. We employed the technique of stepped oxidation, which has previously been used to determine the nitrogen chemistry of a variety of meteoritic and terrestrial rocks.

A trapped nitrogen component in angrites

Chondrule cooling rates are one of the important constraints on chondrule formation and can be used to distinguish between different chondrule formation mechanisms. Here we have modelled diffusion profiles observed across the boundary between forsteritic-olivine relict grains and more fayalitic overgrowth. We show that the cooling of chondrules is complex and good model fits are produced with non-linear cooling rates, offering additional scope for constraining the origin of chondrules.

Cooling rates of chondrules from diffusion profiles in relict olivine grains

The geochemistry and textures of phosphate minerals can provide insights into the geological histories of parental asteroids, but the processes governing their formation and deformation remain poorly constrained We assessed phosphorus-bearing minerals in the three lithologies (light, dark, and melt) of the Chelyabinsk (LL5) ordinary chondrite using scanning electron microscope, electron microprobe, cathodoluminescence, and electron backscatter diffraction techniques The majority of studied phosphate grains appear intergrown with olivine However, microtextures of phosphates (apatite [Ca5(PO4)3(OH,Cl,F)] and merrillite [Ca9NaMg(PO4)7]) are extremely variable within and between the differently shocked lithologies investigated We observe continuously strained as well as recrystallized strain-free merrillite populations Grains with strain-free subdomains are present only in the more intensely shocked dark lithology, indicating that phosphate growth predates the development of primary shock-metamorphic features Complete melting of portions of the meteorite is recorded by the shock-melt lithology, which contains a population of phosphorus-rich olivine grains The response of phosphorus-bearing minerals to shock is therefore hugely variable throughout this monomict impact breccia We propose a paragenetic history for P-bearing phases in Chelyabinsk involving initial phosphate growth via P-rich olivine replacement, followed by phosphate deformation during an early impact event This event was also responsible for the local development of shock melt that lacks phosphate grains and instead contains P-enriched olivine We generalize our findings to propose a new classification scheme for Phosphorus-Olivine-Assemblages (Type I–III POAs) We highlight how POAs can be used to trace radiogenic metamorphism and shock metamorphic events that together span the entire geological history of chondritic asteroids

https://onlinelibrary.wiley.com/doi/pdf/10.1111/maps.13648

Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus-Olivine-Assemblages in chondrites

croscope of lunar meteorite LAP 04841. Top – crossed-polar view of a whole thinsection. Buttons on the right allow users to switch from plane polarized light (PPL) to crossed polars (XPL), vary magnification, pan around, zoom in an out on an area of interest, and overlay a grid or scale. Bottom – the two circular areas are rotation movies in PPL (left) and XPL (right). The user can rotate these two circles simultaneously something not possible with a real microscope! VIRTUAL MICROSCOPE FOR EXTRA-TERRESTRIAL SAMPLES: A NEW TOOL FOR PUBLIC ENGAGEMENT IN PLANETARY SCIENCES M. Anand 1,2 , S. P. Kelley 1 , A. G. Tindle 1 and P. C. Whalley 3 , 1 Department of Earth and Environmental Sciences, CEPSAR, Open University, Milton Keynes, MK7 6AA, UK (m.anand@open.ac.uk) 2 Department of Mineralogy, The Natural History Museum, London, SW7 5BD, UK. 3 Knowledge Media Institute, Open University, Milton Keynes, MK7 6AA, UK

Mahesh Anand

Papers

Aqueous alteration of Nakhlites: implications for water on Mars

A trapped nitrogen component in angrites

Cooling rates of chondrules from diffusion profiles in relict olivine grains

Microtextures in the Chelyabinsk impact breccia reveal the history of Phosphorus-Olivine-Assemblages in chondrites

Virtual Microscope for Extra-Terrestrial Samples: A New Tool for Public Engagement in Planetary Sciences