Mapping of the cusp plasma precipitation on the surface of Mercury

The presence of a magnetosphere around Mercury plays a fundamental role on the way the solar wind plasma interacts with the planet. Since the observations suggest that Mercury should occupy a large fraction of its magnetosphere and because of lack of an atmosphere, significant differences in solar wind-magnetosphere coupling are expected to exist with respect to the Earth case. On the basis of a modified Tsyganenko T96 model we describe the geometry of the magnetic field that could characterize Mercury, and its response to the variations of the impinging solar wind and of the interplanetary magnetic field. The investigation is focused on the shape and dimension of the open magnetic field regions (cusps) that allow the direct penetration of magnetosheath plasma through the exosphere of Mercury, down to its surface. The precipitating particle flux and energy are evaluated as a function of the open field line position, according to different solar wind conditions. A target of this study is the evaluation of the sputtered particles from the crust of the planet, and their contribution to the exospheric neutral particle populations. Such estimates are valuable in the frame of a neutral particle analyser to be proposed on board of the ESA/BepiColombo mission.     

CUBES: cassegrain U-band Brazil-ESO spectrograph

CUBES is a high-efficiency, medium-resolution (R～20,000) ground based UV (300–400 nm) spectrograph, to be installed in the cassegrain focus of one of ESO’s VLT unit telescopes in 2017/18. The CUBES project is a joint venture between ESO and IAG/USP, and LNA/MCTI. CUBES will provide access to a wealth of new and relevant information for stellar as well as extragalactic sources. Main science cases include the study of beryllium and heavy elements in metal-poor stars, the direct determination of carbon, nitrogen and oxygen abundances by study of molecular bands in the UV range, as well as the study of active galactic nuclei and the quasar absorption lines. With a streamlined modern instrument design, high efficiency dispersing elements and UV-sensitive detectors, it will give a significant gain in sensitivity over existing ground based medium-high resolution spectrographs, enabling vastly increased sample sizes accessible to the astronomical community. We present here a brief overview of the project including the status, science cases and a discussion of the design options.     

Discrimination of agricultural crops in a tropical semi-arid region of Brazil based on L-band polarimetric airborne SAR data

Recent articles are indicating that polarimetric data provide significantly more information than conventional or multi-polarized images, particularly due to the additional phase information. The objective of this paper is to evaluate the multi-polarized and fully polarimetric L-band airborne SAR-R99B data, in terms of their capability to distinguish among different agricultural crops in the western part of Bahia State, Brazil. Emphasis was given to coffee, cotton and pasture crops which were at well developed growing stages. Discrimination among crops was carried out using graphical analysis of mean backscatter values. Crop classification was performed for single and multiple polarizations, and fully polarimetric images with a classifier that uses the contextual Iterated Conditional Modes–ICM algorithm. The investigation confirmed the potential of L-band multi-polarized and polarimetric airborne SAR-R99B data to distinguish and classify agricultural crops in the tropical condition of the test-site. In addition, it clearly indicated the gradual and considerable improvement that was achieved going from single to three polarizations and from multi-polarized to fully polarimetric images.     

Volcanic and structural history of the rocks exposed at Pickering Crater (Daedalia Planum, Mars)

In the western hemisphere of Mars Amazonian volcanism from Arsia Mons produced the smooth surfaces of Daedalia Planum and masks older rocks. Close to the southern termination of Daedalia Planum basement rocks are exposed in which are preserved craters that escaped or were only partially filled by this most recent volcanism. Pickering Crater is an approximately 130 km diameter crater. The youngest lavas flowed into this crater from Daedalia Planum by way of a NW rim breach, covering its western part. East of a well-defined flow front an older lava sequence with a distinctive platy surface and derived from a more proximal unestablished source to the northeast is exposed. Several units are identified within this sequence on the basis of surface texture, which is more subdued in progressively older rocks. Only local mapping of the flow front boundaries of these units is possible because of incomplete coverage by high resolution imagery. During emplacement of the older lavas a NE-SW striking en echelon graben system and parallel smaller troughs and dikes formed under inferred regional NW-SE extension. A much earlier strike-slip regime pre-dating the lavas exposed in the crater floor is postulated, based on the highly fretted nature of the rim of Pickering Crater and an elongated smaller crater to its northeast, approximately 40 km long in the NE-SW direction. The rims of these craters contrast with that of a smoother rimmed impact crater in the southeast that was excavated subsequent to strike-slip deformation but prior to the emplacement of platy surfaced lavas.     

Location of the bow shock and ion composition boundaries at Venus—initial determinations from Venus Express ASPERA-4

For the first time since 1992 when the Pioneer Venus Orbiter (PVO) ceased to operate, there is again a plasma instrument in orbit around Venus, namely the ASPERA-4 flown on Venus Express (inserted into an elliptical polar orbit about the planet on April 11, 2006). In this paper we report on measurements made by the ion and electron sensors of ASPERA-4 during their first five months of operation and, thereby, determine the locations of both the Venus bow shock (BS) and the ion composition boundary (ICB) under solar minimum conditions. In contrast to previous studies based on PVO data, we employ a 3-parameter fit to achieve a realistic shape for the BS. We use a different technique to fit the ICB because this latter boundary cannot be represented by a conic section. Additionally we investigate the dependence of the location of the BS on solar wind ram pressure (based on ASPERA-4 solar wind data) and solar EUV flux (using a proxy from Earth).     

Catastrophic precipitation‐triggered lahar at Casita volcano,Nicaragua: occurrence,bulking and transformation

A catastrophic lahar began on 30 October 1998, as hurricane precipitation triggered a small ?ank collapse of Casita volcano, a complex and probably dormant stratovolcano. The initial rockslide‐debris avalanche evolved on the ?ank to yield a watery debris ?ood with a sediment concentration less than 60 per cent by volume at the base of the volcano. Within 2·5 km, however, the watery ?ow entrained (bulked) enough sediment to transform entirely to a debris ?ow. The debris ?ow, 6 km downstream and 1·2 km wide and 3 to 6 m deep, killed 2500 people, nearly the entire populations of the communities of El Porvenir and Rolando Rodriguez. These ‘new towns’ were developed in a prehistoric lahar pathway: at least three ?ows of similar size since 8330 ¹⁴C years bp are documented by stratigraphy in the same 30‐degree sector. Travel time between perception of the ?ow and destruction of the towns was only 2·5–3·0 minutes. The evolution of the ?ow wave occurred with hydraulic continuity and without pause or any extraordinary addition of water. The precipitation trigger of the Casita lahar emphasizes the need, in volcano hazard assessments, for including the potential for non‐eruption‐related collapse lahars with the more predictable potential of their syneruption analogues. The ?ow behaviour emphasizes that volcano collapses can yield not only volcanic debris avalanches with restricted runouts, but also mobile lahars that enlarge by bulking as they ?ow. Volumes and hence inundation areas of collapse‐runout lahars can increase greatly beyond their sources: the volume of the Casita lahar bulked to at least 2·6 times the contributing volume of the ?ank collapse and 4·2 times that of the debris ?ood. At least 78 per cent of the debris ?ow matrix (sediment < ?1·0Φ; 2 mm) was entrained during ?ow. Copyright © 2004 John Wiley & Sons, Ltd.     

Seismological constraints on the 2018 Mt. Etna (Italy) flank eruption and implications for the flank dynamics of the volcano

3D earthquake locations, focal mechanisms and stress tensor distribution in a 16‐month interval covering the 2018 Mt. Etna flank eruption, enabled us to investigate the relationship between magma intrusion and structural response of the volcano and shed light on the dynamic processes affecting the instability of Mt. Etna. The magma intrusion likely caused tension in the flanks of the volcano, leading to significant ground deformation and redistribution of stress on the neighbouring faults at the edge of Mt. Etna's unstable sector, encouraging the ESE sliding of the eastern flank of the volcano. Accordingly, FPSs of the post‐eruptive events show strike slip faulting mechanisms, under a stress regime characterized by a maximum compressive σ₁, NE‐SW oriented. In this perspective, any flank eruption could temporarily enhance the sliding process of both the southern and eastern flanks of the volcano.