Radar observations of Itokawa in 2004 and improved shape estimation

Abstract— We present June 2004 radar images of asteroid 25143 Itokawa (1998 SF36) that improve upon the longitude‐latitude coverage of images obtained in 2001 by Ostro et al. (2004) and use the 2001–2004 data to refine that paper's constraints on Itokawa's shape. The 2004 images, the first of the asteroid's southern side, look distinctly different from the 2001 images, revealing leading edges that are much more curved and rugged than the nearly convex leading edges seen at northern latitudes in 2001. Itokawa is shaped like a slightly asymmetrical, bent, lumpy ellipsoid with dimensions along the principal axes within 10% of 594 times 320 times 288 m. To illustrate the uncertainty space associated with shape reconstruction from images with suboptimal orientational coverage, we present two alternative three‐dimensional models of the object.     

A late Early Pleistocene pollen record from Fontana Ranuccio (central Italy)

A pollen record from a sediment core drilled underneath the Acheulian site of Fontana Ranuccio provides new data on the vegetation characters in central Italy during the late Early Pleistocene, in a forest phase possibly corresponding to a substage of Marine Isotope Stage 21. A number of tree taxa nowadays extinct in Europe (Cathaya, Tsuga, Taxodium type, Carya and Pterocarya) are present at Fontana Ranuccio in a temperate phase characterised by dense forest conditions, dominated by Alnus and Pterocarya. The comparison of the Fontana Ranuccio record with other dated sites distributed along the Italian peninsula indicates that the floristic and vegetational characters of the Mid Pleistocene revolution present a rather distinct succession of biostratigraphic events. Compared to other Early Pleistocene pollen records from southern Europe, the Italian Peninsula shows greater floristic similarities with the Eastern Mediterranean regions than with the Iberian Peninsula. Copyright © 2011 John Wiley & Sons, Ltd.     

Physical properties of near-Earth Asteroid (33342) 1998 WT24

During its close Earth approach in 2001, the E-class near-Earth Asteroid (33342) 1998 WT24 was the focus of extensive radar, optical, and thermal infrared observations. We present a physical model of this object, estimated from Arecibo and Goldstone radar images that cover multiple rotations and span over 100° of sky motion. The asteroid has an equivalent diameter of 415±40 m and a diffuse radar scattering law that is identical in both senses of circular polarization, implying a surface that is extremely rough on centimeter-to-decimeter scales. The shape is dominated by three large basins, which may be impact craters or a relic of past dynamical disruption of the object. Analysis of YORP perturbations on WT24's spin state predicts that the asteroid's spin rate is decreasing at a rate of . Simply extrapolating this rate suggests that the asteroid will despin over the next 150 kyr and was spinning at its surface disruption rate 75 kyr ago, but the rotational evolution of WT24 depends on the surface's thermal properties and probably is more complex than a simple spin-down.     

Assessing anthropogenic impacts on limited water resources under semi-arid conditions: three-dimensional transient regional modelling in Jordan

Both increasing aridity and population growth strongly stress freshwater resources in semi-arid areas such as Jordan. The country’s second largest governorate, Irbid, with over 1 million inhabitants, is already suffering from an annual water deficit of 25 million cubic meters (MCM). The population is expected to double within the next 20 years. Even without the large number of refugees from Syria, the deficit will likely increase to more then 50 MCM per year by 2035 The Governorate’s exclusive resource is groundwater, abstracted by the extensive Al Arab and Kufr Asad well fields. This study presents the first three-dimensional transient regional groundwater flow model of the entire Wadi al Arab to answer important questions regarding the dynamic quality and availability of water within the catchment. Emphasis is given to the calculation and validation of the dynamic groundwater recharge, derived from a multi-proxy approach, including (1) a hydrological model covering a 30-years dataset, (2) groundwater level measurements and (3) information about springs. The model enables evaluation of the impact of abstraction on the flow regime and the groundwater budget of the resource. Sensitivity analyses of controlling parameters indicate that intense abstraction in the southern part of the Wadi al Arab system can result in critical water-level drops of 10 m at a distance of 16 km from the production wells. Moreover, modelling results suggest that observed head fluctuations are strongly controlled by anthropogenic abstraction rather than variable recharge rates due to climate changes.     

Holocene environmental instability in the wetland north of the Tiber delta (Rome,Italy): sea-lake-man interactions

Combined analyses of pollen, seeds, woods, micro-charcoal and non-pollen palynomorphs from Stagno di Maccarese, an artificially dried out coastal basin north of the Tiber delta now occupied by the Fiumicino Airport (Rome, Italy), document marked vegetation and environmental changes during the last 8300 years. Between 8300 and 5400 cal. a BP dense mixed deciduous and evergreen forests surrounded a eutrophic freshwater basin. An abrupt change around 5400 cal. a BP marks the transition to a marshy environment, due to a lowering of the water table. An increase of cereals and micro-charcoals matches the presence of a nearby Eneolithic settlement. Between 5100 and 2900 cal. a BP there is a remarkable expansion of riparian trees, indicating an increase of the water level. Between 2900 and 2000 cal. a BP, a new development of marshlands points to a progressive lowering of the lake. After 2000 cal. a BP, during the Roman exploitation of the area, an expansion of arboreal vegetation is recorded, characterized by evergreen and deciduous oak-dominated forests, while an extensive chenopods marshland matches the presence of saltworks. On the whole, the Stagno di Maccarese area appears very unstable, due to changes in lake level, introgression of marine water, eutrophic phases, flood events, desiccations and openings of the forest vegetation.     

Radar observations and a physical model of Asteroid 1580 Betulia

We report Arecibo (2380-MHz, 13-cm) observations of Asteroid 1580 Betulia in May-June 2002. We combine these continuous-wave Doppler spectra and delay-Doppler images with optical lightcurves from the 1976 and 1989 apparitions in order to estimate Betulia's shape and spin vector. We confirm the spin vector solution of Kaasalainen et al. [Kaasalainen, M., and 21 colleagues, 2004. Icarus 167, 178-196], with sidereal period P=6.13836 h and ecliptic pole direction (λ,β)=(136°,+22°), and obtain a model that resembles the Kaasalainen et al. convex-definite shape reconstruction but is dominated by a prominent concavity in the southern hemisphere. We find that Betulia has a maximum breadth of 6.59±0.66 km and an effective diameter of 5.39±0.54 km. These dimensions are in accord with reanalyzed polarimetric and radar data from the 1970s. Our effective diameter is 15% larger than the best radiometric estimate of Harris et al. [Harris, A.W., Mueller, M., Delbó, M., Bus, S.J., 2005. Icarus 179, 95-108], but this difference is much smaller than the size differences between past models. Considering orbits of test particles around Betulia, we find that this asteroid's unusual shape results in six equilibrium points close to its equatorial plane rather than the usual four points; two of these six points represent stable synchronous orbits while four are unstable. Betulia's close planetary encounters can be predicted for over four thousand years into the future.     

Radar imaging of Asteroid 7 Iris

Arecibo radar images of Iris obtained in November 2006 reveal a topographically complex object whose gross shape is approximately ellipsoidal with equatorial dimensions within 15% of 253 × 228 km. The radar view of Iris was restricted to high southern latitudes, precluding reliable estimation of Iris’ entire 3D shape, but permitting accurate reconstruction of southern hemisphere topography. The most prominent features, three roughly 50-km-diameter concavities almost equally spaced in longitude around the south pole, are probably impact craters. In terms of shape regularity and fractional relief, Iris represents a plausible transition between ∼50-km-diameter asteroids with extremely irregular overall shapes and very large concavities, and very much larger asteroids (Ceres and Vesta) with very regular, nearly convex shapes and generally lacking monumental concavities.     

Estimates of site seismicity rates using ill-defined macroseismic data

A new approach to the problem of site seismic hazard analysis is proposed, based on intensity data affected by uncertainties. This approach takes into account the ordinal and discrete character of intensities, trying to avoid misleading results due to the assumption that intensity can be treated as a real number (continuous distribution estimators, attenuation relationships, etc.). The proposed formulation is based on the use of a distribution function describing, for each earthquake, the probability that site seismic effects can be described by each possible intensity value. In order to obtain site hazard estimates where local data are lacking, the dependence of this distribution function with the distance from the macroseismic epicenter and with epicentral intensity is examined. A methodology has been developed for the purpose of combining such probabilities and estimating site seismicity rates which takes into account the effect of uncertainties involved in this kind of analysis. An application of this approach is described and discussed.     

Late Quaternary western Mediterranean pollen records and African winds

Late Quaternary vegetation changes of regional and global significance in the Mediterranean region are generally interpreted as being controlled by changes in the circulation patterns of North Atlantic air masses. However, the possibility cannot be excluded that they may also be related to winds blowing from Africa. Long pollen records from southwest Europe show that Cedrus pollen of northwest African provenance is found during the glacial periods, and occasionally during abrupt deforestation events in the forest-dominated periods of the interglacials. A pollen concentration record from central Italy shows that during the Holocene the presence of Cedrus pollen coincides with two abrupt deforestation events, around 8.1 and 4.2 cal kyr BP. These observations raise the question of a possible influence of eolian activity on arboreal vegetation during phases of climatic stress towards aridity, and suggest the use of modern pollen monitoring as a strategy for revealing tendencies towards aridification in southwestern Europe.     

A radar survey of main-belt asteroids: Arecibo observations of 55 objects during 1999-2003

We report Arecibo observations of 55 main-belt asteroids (MBAs) during 1999-2003. Most of our targets had not been detected previously with radar, so these observations more than double the number of radar-detected MBAs. Our bandwidth estimates constrain our targets' pole directions in a manner that is geometrically distinct from optically derived constraints. We present detailed statistical analyses of the disk-integrated properties (radar albedo and circular polarization ratio) of the 84 MBAs observed with radar through March 2003; all of these observations are summarized in the online supplementary information. Certain conclusions reached in previous studies are strengthened: M asteroids have higher mean radar albedos and a wider range of albedos than do other MBAs, suggesting that both metal-rich and metal-poor M-class objects exist; and C- and S-class MBAs have indistinguishable radar albedo distributions, suggesting that most S-class objects are chondritic. Also in accord with earlier results, there is evidence that primitive asteroids from outside the C taxon (F, G, P, and D) are not as radar-bright as C and S objects, but a convincing statistical test must await larger sample sizes. In contrast with earlier work, we find S-class MBAs to have higher circular polarization ratios than other MBAs, indicating greater near-surface structural complexity at decimeter scales, due to different mineralogy (material strength or loss tangent), a different impactor population, or both.