The melting temperature of Earth's mantle provides key constraints on the thermal structures of both the mantle and the core. Through high-pressure experiments and three-dimensional x-ray microtomographic imaging, we showed that the solidus temperature of a primitive (pyrolitic) mantle is as low as 3570 ± 200 kelvin at pressures expected near the boundary between the mantle and the outer core. Because the lowermost mantle is not globally molten, this provides an upper bound of the temperature at the core-mantle boundary (T(CMB)). Such remarkably low T(CMB) implies that the post-perovskite phase is present in wide areas of the lowermost mantle. The low T(CMB) also requires that the melting temperature of the outer core is depressed largely by impurities such as hydrogen.

Samples of the carbonaceous asteroid Ryugu were brought to Earth by the Hayabusa2 spacecraft. We analyzed seventeen Ryugu samples measuring 1-8 mm. CO 2 -bearing water inclusions are present within a pyrrhotite crystal, indicating that Ryugu’s parent asteroid formed in the outer Solar System. The samples contain low abundances of materials that formed at high temperatures, such as chondrules and Ca, Al-rich inclusions. The samples are rich in phyllosilicates and carbonates, which formed by aqueous alteration reactions at low temperature, high pH, and water/rock ratios < 1 (by mass). Less altered fragments contain olivine, pyroxene, amorphous silicates, calcite, and phosphide. Numerical simulations, based on the mineralogical and physical properties of the samples, indicate Ryugu’s parent body formed ~ 2 million years after the beginning of Solar System formation.

In order to interpret the formation mechanism of calcium carbonate polymorphs, we propose and construct a new 'precipitation diagram', which has two variables: the driving force for nucleation and temperature. The precipitation experiments were carried out by mixing calcium chloride and sodium carbonate aqueous solutions. As a result, a calcite-vaterite co-precipitation zone, a vaterite precipitation zone, a vaterite-aragonite co-precipitation zone and an aragonite precipitation zone can be defined. Theoretical considerations suggest that the steady state nucleation theory can explain well the appearance of these four zones, and the first-order importance of the temperature dependency of surface free energy in the nucleation of aragonite. Furthermore, the addition of an impurity will likely result in the change of these energies, and this precipitation diagram gives a new basis for interpreting the nature of the polymorphs precipitated in both inorganic and biological environments.

A way to understand mechanical characteristics of an ultrasonic motor is presented. First, the vibration mode of a stator is calculated using a finite-element method (FEM) code. The path of the elliptic motion of the stator's teeth is obtained. The computed vibration mode at the surface of the stator is compared with that measured by an electrooptical displacement transducer. Next, the contact condition of the rotor/stator is calculated. The displacement and velocity of the rotor/stator, the distortion of the stick/slip area, the rotational speed of the rotor, and the friction loss of the motor are obtained. The calculated rotor displacement and torque-rotational speed curve correspond closely to the experimentally measured ones. The internal loss of the rotor/stator and the loss of the supporting felt are measured. The total loss of these losses and the calculated friction loss agree with the measured total loss. The calculated and the measured efficiency of the motor also agree.

Crystallization of groundmass minerals may record the physicochemical conditions of magmatic processes upon eruption and is thus a topic of interdisciplinary research in the disciplines of mineralogy, petrology, and volcanology. Recent studies have reported that the groundmass crystals of some volcanic rocks exhibit a break in their crystal size distribution (CSD) slopes that range from a few micrometers to hundreds of nanometers. The crystals consisting of the finer parts of the break were defined as nanolites. In this study, we report the presence of nanometer-scale crystals down to 1 nm in the pyroclasts of the 2011 eruption of Shinmoedake, the Kirishima volcano group, based on field emission-scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM).We discovered a gap (hiatus) from ~100 to ~30 nm in the size distribution of pyroxene in a dense juvenile fragment of a vulcanian explosion. The pyroxene crystals ~20-30 nm on a diameter were ferroaugite (C2/c), while those a few hundred nanometers in width had a composite structure consisting of the domains of orthopyroxene (Pbca), augite (C2/c), and sub-calcic augite (C2/c). In high-angle annular dark-field scanning TEM images of the same sample, bright spots ~1-2 nm in diameter were recognized with a gap in size from ~10-20 nm titanomagnetite (Fd3m). They are presumed to have Fe-rich compositions, although their phases were too small to be determined. In addition, we found that crystals smaller than a few tens of nanometers for pyroxene and 100 nm for plagioclase did not exist or their number densities were too low for accurate determination. This indicates that there are practical minimum sizes of the crystals. These observations show that nucleation of the nanoscale crystals almost paused (froze) in the late stage of groundmass crystallization, possibly due to a decrease in undercooling, increase in interfacial free energy, and decrease in diffusivity in a dehydrated melt, whereas crystal growth was mostly continuous. In this paper, we introduce the novel term "ultrananolite," to refer to crystals smaller than 30 nm in diameter, and redefine "nanolite" simply as those 30 nm to 1 μm in width, complementing the size interval of crystals in volcanic groundmass smaller than microlites (1-30 μm). In the transient nucleation process, the presence of subcritical size clusters is required. The observed ultrananolite-sized particles might partly include subcritical clusters. The difference in the slope of CSDs, presence of gaps in size distribution, and minimum crystal size among the eruption styles of the 2011 Shinmoedake eruption may be interpreted by considering the difference in magma residence time and fragmentation pressure in the shallow conduit, and possibly the rewelding process in the crater.

The relationship between Raman spectra and crystallographic orientation was examined for single crystals of Fo 89 Fa 11 olivine [(Mg 0.89 Fe 0.11 ) 2 SiO 4 ]. Raman spectra were obtained for chemically homogeneous olivine grains with various orientations on a thin section of mantle-derived rock (dunite) using micro-Raman equipment and an unpolarized exciting laser. Crystallographic orientations of each olivine grain were determined using an electron backscattered diffraction (EBSD) method. Five apparent peaks at 822 (peak 1), 854 (peak 2), 880 (peak 3), 917 (peak 4), and 959 cm −1 (peak 5) were observed in the spectral range of 700-1050 cm −1 . Intensity ratios of peak i to peak 2, I i /I 2 , for i = 1, 4, and 5 were formulated empirically as functions of crystallographic orientations: I i /I 2 = .a 1i q 2 /p 2 + a 2i q/p + a 3i / sin 2 f + .b 1i q 2 /p 2 + b 2i q/p + b 3i / sin f + c i where a 1i , a 2i , a 3i , b 1i , b 2i , b 3i , c i are constants. f is the angle between the [100] axis and the incident direction of the laser, and q is the angle between the [001] axis and the incident direction of laser projected on the f100g plane. These equations well describe the relationships between I i /I 2 and crystallographic orientation. The obtained empirical equations enable Raman spectroscopic determination of the crystallographic orientation of olivine.

Discovery of fossil asteroidal ice in a meteorite provides new insight into asteroid formation in the early Solar System.

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