Vesta's mineralogical composition as revealed by the visible and infrared spectrometer on Dawn

The Dawn spacecraft mission has provided extensive new and detailed data on Vesta that confirm and strengthen the Vesta–howardite–eucrite–diogenite (HED) meteorite link and the concept that Vesta is differentiated, as derived from earlier telescopic observations. Here, we present results derived by newly calibrated spectra of Vesta. The comparison between data from the Dawn imaging spectrometer—VIR—and the different class of HED meteorites shows that average spectrum of Vesta resembles howardite spectra. Nevertheless, the Vesta spectra at high spatial resolution reveal variations in the distribution of HED‐like mineralogies on the asteroid. The data have been used to derive HED distribution on Vesta, reported in Ammannito et al. (2013), and to compute the average Vestan spectra of the different HED lithologies, reported here. The spectra indicate that, not only are all the different HED lithologies present on Vesta, but also carbonaceous chondritic material, which constitutes the most abundant inclusion type found in howardites, is widespread. However, the hydration feature used to identify carbonaceous chondrite material varies significantly on Vesta, revealing different band shapes. The characteristic of these hydration features cannot be explained solely by infalling of carbonaceous chondrite meteorites and other possible origins must be considered. The relative proportion of HEDs on Vesta's surface is computed, and results show that most of the vestan surface is compatible with eucrite‐rich howardites and/or cumulate or polymict eucrites. A very small percentage of surface is covered by diogenite, and basaltic eucrite terrains are relatively few compared with the abundance of basaltic eucrites in the HED suite. The largest abundance of diogenitic material is found in the Rheasilvia region, a deep basin, where it clearly occurs below a basaltic upper crust. However, diogenite is also found elsewhere; although the depth to diogenite is consistent with one magma ocean model, its lateral extent is not well constrained.     

Toward high spatial resolution in solar observations

To achieve high spatial resolution capability for IR solar observations, we suggest the use of a special mask placed before the entrance aperture of large conventional optical telescopes. Such a mask would match well the resolution of a non-redundant array and would provide safe operation of a large telescope used for solar observations. The proposed solution has the additional advantage of relatively low cost because already-existing optical telescopes are used.     

Spada: An Array of Spad Detectors For Astrophysical Applications

Astrophysical studies require accurate, sensitive and fast detectors to detect faint sources with high variability. Recently an array of Single Photon Avalanche Diodes (SPAD), SPADA, has been developed. This array is suitable for competitive adaptive optics operations and fast transient image acquisition at a fraction of the current cost of imaging arrays. The fabricated solid-state photon counters are rugged, easily integrated with the optics, free from readout noise, and have very fast frame rates (> 10 kHz, for visible corrections) with nanosecond electronic gating. In this paper, the following are described: the development of silicon monolithic arrays of 60 photon-counters, the detection electronics (based on integrated active quenching circuits for each pixel of the array), the real-time data-processing board implemented into FPGA and some aspects of the mechanical housing.     

Ocean's philosophical images

From early Greek cosmology and pre-socratic thought to Kant, Nietzsche and the philosophy of existence, ‘ocean’ is a figure of the most relevant significance, in accordance with two different patterns: as mythical representation of the principle of the universe and as metaphor of the adventure of human knowledge. Now the question could be: do the philosophical images of the ocean have some value for modern science?     

Fault-controlled Soil CO2 Degassing and Shallow Magma Bodies: Summit and Lower East Rift of Kilauea Volcano (Hawaii), 1997

Soil CO₂ flux measurements were carried out along traverses across mapped faults and eruptive fissures on the summit and the lower East Rift Zone of Kilauea volcano. Anomalous levels of soil degassing were found for 44 of the tectonic structures and 47 of the eruptive fissures intercepted by the surveyed profiles. This result contrasts with what was recently observed on Mt. Etna, where most of the surveyed faults were associated with anomalous soil degassing. The difference is probably related to the differences in the state of activity at the time when soil gas measurements were made: Kilauea was erupting, whereas Mt. Etna was quiescent although in a pre-eruptive stage. Unlike Mt. Etna, flank degassing on Kilauea is restricted to the tectonic and volcanic structures directly connected to the magma reservoir feeding the ongoing East Rift eruption or in areas of the Lower East Rift where other shallow, likely independent reservoirs are postulated. Anomalous soil degassing was also found in areas without surface evidence of faults, thus suggesting the possibility of previously unknown structures. Received: November 2003, revised: January 2005, accepted: January 2005     

The southernmost record of tropical pollen grains in the mid-Cretaceous of Patagonia, Argentina

Pollen grains characteristic of tropical Northern Gondwana (Schrankipollis, Brenneripollis and Pennipollis peroreticulatus) have been recorded from the Cretaceous of Patagonia. They were recovered from the Late Albian–Cenomanian Kachaike Formation in Santa Cruz Province, southern Argentina. The palynological assemblages are dominated by gymnosperm pollen and bryophyte-pteridophyte spores, whereas angiosperms are poorly represented. The angiospermoid type Schrankipollis has not been reported previously from Argentina, and a new species S. kachaikensis is described. Two species of Brenneripollis (of uncertain affinity) and Pennipollis peroreticulatus (related to the Alismatales) are also reported. The first appearances of Pennipollis peroreticulatus are clearly diachronous from north to south, ranging from the Barremian in tropical regions to the Coniacian–Santonian in Antarctica. S. kachaikensis and P. peroreticulatus show restricted stratigraphic distributions through the Kachaike Formation and may be stratigraphically useful markers. A tetrad of Walkeripollis (related to modern Winteraceae) is also recognized. This is the oldest record of Winteraceae in the southern temperate region where the family lives today. Evidence for migration of Winteraceae from tropical Gondwana to Antarctica and Australia throughout South America, is provided by this new finding. The presence of tropical elements in the austral margin of South America gives support to previous studies on the expansion of warm temperatures towards high latitudes during the mid Cretaceous.     

Seismically induced rock slope failures resulting from topographic amplification of strong ground motions: The case of Pacoima Canyon, California

The 1994 Northridge earthquake (M_w = 6.7) triggered extensive rock slope failures in Pacoima Canyon, immediately north of Los Angeles, California. Pacoima Canyon is a narrow and steep canyon incised in gneissic and granitic rocks. Peak accelerations of nearly 1.6 g were recorded at a ridge that forms the left abutment of Pacoima Dam; peak accelerations at the bottom of the canyon were less than 0.5 g, suggesting the occurrence of topographic amplification. Topographic effects have been previously suggested to explain similarly high ground motions at the site during the 1971 (M_w = 6.7) San Fernando earthquake. Furthermore, high landslide concentrations observed in the area have been attributed to unusually strong ground motions rather than higher susceptibility to sliding compared with nearby zones. We conducted field investigations and slope stability back-analyses to confirm the impact of topographic amplification on the triggering of landslides during the 1994 earthquake. Our results suggest that the observed extensive rock sliding and falling would have not been possible under unamplified seismic conditions, which would have generated a significantly lower number of areas affected by landslides. In contrast, modelling slope stability using amplified ground shaking predicts slope failure distributions matching what occurred in 1994. This observation confirms a significant role for topographic amplification on the triggering of landslides at the site, and emphasises the need to select carefully the inputs for seismic slope stability analyses.     

Multimode migration of scattered and converted waves for the structure of the Hikurangi slab interface, New Zealand

Reflectivity imaging of local earthquake seismograms has revealed the structure of the Hikurangi subduction interface at the location of two strong earthquakes that occurred in 1990. The earthquakes originated within the continental plate of the North Island of New Zealand and below in the subducting Pacific slab. We used seismograms from 500 well-located events in two earthquake sequences recorded by a small temporary seismograph deployment to directly image the structure and multiphase reflectivity of the plate interface. Synthetic tests of the imaging method show the effects of the poor 3-d geometric coverage afforded by the seismometer array. Kirchhoff summation image sections computed from synthetics show accurate depth imaging of backscattering interfaces. Phase-converting interfaces imaged with forward-scattered waves are smeared by poor ray coverage to 5-km depth inaccuracy and are only imaged over a small range of their horizontal extent. From the data, we computed image sections for P–P, P–S, S–P and S–S scattering. We mitigated imaging artifacts due to poor ray coverage with an obliquity factor, an antialiasing criterion and enhancement by resampling statistics. Imaging used a sharply layered velocity model. We tested for the effects of imaging with first-arriving headwaves by imaging through smoothly varying velocity models. For our ray geometry, early-arrival headwaves contribute little to the images.The plate interface appears as a 3–5-km thick P–P and possibly S–S backscatterer with 5° NW dip, offset 5 km down-to-the-NW above a normal fault in the slab. When illuminated from below, a wedge of the interface on the downdip side of the slab fault forms a very prominent P–P forward scatterer. The edges of the wedge forward-scatter some S–P and S–S energy, but an order of magnitude less than the P–P forward scattering. The imbalances between forward scattering of P and S energy suggest a wedge of subducted sediment retaining significant porosity but with rigidity close to that of surrounding rocks.