Farside explorer: unique science from a mission to the farside of the moon

Farside Explorer is a proposed Cosmic Vision medium-size mission to the farside of the Moon consisting of two landers and an instrumented relay satellite. The farside of the Moon is a unique scientific platform in that it is shielded from terrestrial radio-frequency interference, it recorded the primary differentiation and evolution of the Moon, it can be continuously monitored from the Earth–Moon L2 Lagrange point, and there is a complete lack of reflected solar illumination from the Earth. Farside Explorer will exploit these properties and make the first radio-astronomy measurements from the most radio-quiet region of near-Earth space, determine the internal structure and thermal evolution of the Moon, from crust to core, and quantify impact hazards in near-Earth space by the measurement of flashes generated by impact events. The Farside Explorer flight system includes two identical solar-powered landers and a science/telecommunications relay satellite to be placed in a halo orbit about the Earth–Moon L2 Lagrange point. One lander would explore the largest and oldest recognized impact basin in the Solar System— the South Pole–Aitken basin—and the other would investigate the primordial highlands crust. Radio astronomy, geophysical, and geochemical instruments would be deployed on the surface, and the relay satellite would continuously monitor the surface for impact events.     

A PRINCIPAL AXIS SHIFT IN THE AMERICAN SPATIAL ECONOMY?*

Gottmann in his classic Megalopolis attributes the dominance of the Northeast to its function as the hinge region of the United States. In this paper, we show, via statistics on maritime trade and interregional freight traffic by rail, that Megalopolis is no longer the dominant “hinge” region. We present evidence that the Gulf region may be supplanting it in this function. Finally, we speculate on some of the reasons for the Gulf's rather sudden assumption of this role and its implications for the economic geography of the U.S.     

A spectroscopic comparison of HED meteorites and V-type asteroids in the inner Main Belt

V-type asteroids in the inner Main Belt (a < 2.5 AU) and the HED meteorites are thought to be genetically related to one another as collisional fragments from the surface of the large basaltic Asteroid 4 Vesta. We investigate this relationship by comparing the near-infrared (0.7-2.5 μm) spectra of 39 V-type asteroids to laboratory spectra of HED meteorites. The central wavelengths and areas spanned by the 1 and 2 μm pyroxene-olivine absorption bands that are characteristic of planetary basalts are measured for both the asteroidal and meteoritic data. The band centers are shown to be well correlated, however the ratio of areas spanned by the 1 and 2 μm absorption bands are much larger for the asteroids than for the meteorites. We argue that this offset in band area ratio is consistent with our currently limited understanding of the effects of space weathering, however we cannot rule out the possibility that this offset is due to compositional differences. Several other possible causes of this offset are discussed.Amongst these inner Main Belt asteroids we do not find evidence for non-Vestoid mineralogies. Instead, these asteroids seem to represent a continuum of compositions, consistent with an origin from a single differentiated parent body. In addition, our analysis shows that V-type asteroids with low inclinations (i < 6°) tend to have band centers slightly shifted towards long wavelengths. This may imply that more than one collision on Vesta’s surface was responsible for producing the observed population of inner belt V-type asteroids. Finally, we offer several predictions that can be tested when the Dawn spacecraft enters into orbit around Vesta in the summer of 2011.     

Late Quaternary secular variation of geomagnetic declination in western New York

A secular variation record of the geomagnetic declination has been obtained from glaciolacustrine varved clays and postglacial sediments, sampled both from outcrop and from piston cores from Lake Ontario. It appears to be uninterrupted and covers the interval 14,000 years B.P. (¹⁴C) to the present. The record for the interval 14,000–12,300 years B.P. consists of true declination and was obtained from samples collected from outcrop. The record for the interval 12,500 + years B.P. to the present consists of relative declination and was obtained from piston cores. The secular variation record is internally consistent and is compatible with the chronology of events known to have occurred during and following the deglaciation of western New York. Use of the record for magnetic correlation within the study area is demonstrated.     

The challenge of numerically implementing numerous force–resultant models in the stability analysis of long on-bottom pipelines

Plasticity models written directly in terms of force and displacement are finding increased popularity in describing the behaviour of offshore foundations. However, when applied to the on-bottom stability analysis of pipelines under random storm loading, hundreds, if not thousands, of models must be incorporated with structural elements in a three-dimensional analysis and simultaneously solved. This necessitates extremely efficient and accurate numerical integration techniques. This paper scrutinizes constitutive integration algorithms within both explicit and implicit frameworks, and applies them to a two-surface mixed hardening model that describes the force–displacement behaviour of a pipe partially embedded in sand. Detailed solutions are provided, allowing implementation of the pipe–soil model into any standard structural finite-element program. Through use of practical examples, the efficiency and accuracy of the solution methods are assessed.     

A simulation of probabilistic wildfire risk components for the continental United States

This simulation research was conducted in order to develop a large-fire risk assessment system for the contiguous land area of the United States. The modeling system was applied to each of 134 Fire Planning Units (FPUs) to estimate burn probabilities and fire size distributions. To obtain stable estimates of these quantities, fire ignition and growth was simulated for 10,000 to 50,000 “years” of artificial weather. The fire growth simulations, when run repeatedly with different weather and ignition locations, produce burn probabilities and fire behavior distributions at each landscape location (e.g., number of times a “cell” burns at a given intensity divided by the total years). The artificial weather was generated for each land unit using (1) a fire danger rating index known as the Energy Release Component (ERC) which is a proxy for fuel moisture contents, (2) a time-series analysis of ERC to represent daily and seasonal variability, and (3) distributions of wind speed and direction from weather records. Large fire occurrence was stochastically modeled based on historical relationships to ERC. The simulations also required spatial data on fuel structure and topography which were acquired from the LANDFIRE project (). Fire suppression effects were represented by a statistical model that yields a probability of fire containment based on independent predictors of fire growth rates and fuel type. The simulated burn probabilities were comparable to observed patterns across the U.S. over the range of four orders of magnitude, generally falling within a factor of 3 or 4 of historical estimates. Close agreement between simulated and historical fire size distributions suggest that fire sizes are determined by the joint distributions of spatial opportunities for fire growth (dependent on fuels and ignition location) and the temporal opportunities produced by conducive weather sequences. The research demonstrates a practical approach to using fire simulations at very broad scales for purposes of operational planning and perhaps ecological research.     

Pi 2 pulsations and the eastward electrojet: A case study

We report the results of a case study of two Pi 2 pulsations observed near the eastward electrojet by the Scandinavian Magnetometer Array. The power of the two Pi 2 pulsations, calculated using a standard Fast Fourier Transform method, peaks near the centre of the eastward electrojet. For both events there is a strong latitudinal gradient in the power poleward of the equatorward border of the electrojet. The sense of polarisation is predominantly clockwise at the northern stations and anticlockwise at the southern stations although the reversal from clockwise to anticlockwise does not occur at a constant latitude. For the first event the polarisation reversal occurs at higher latitudes in the western half of the array; for the second the polarisation reversal occurs at higher latitudes at the edges of the array. The polarisation reversal does not appear to be related to the location of the eastward electrojet. Equivalent current vectors of the Pi 2 pulsations, obtained by rotating the band pass filtered data through 90°, exhibit clear vortex structures in both events. The vortices change sense of direction at half the period of the Pi 2 pulsation. A simple model for the ionospheric electric field in accord with the field line resonance theory reconstructs the basic features of the observed Pi 2 equivalent current system. We thus conclude that Pi 2 signatures in the region of the eastward electrojet and far away from the auroral break-up region are governed by the field line resonance mechanism.     

A search for planets transiting the M-dwarf debris disc host, AU Microscopii

We present high-cadence, high-precision multiband photometry of the young, M1Ve, debris disc star, AU Microscopii. The data were obtained in three continuum filters spanning a wavelength range from 4500 to 6600 Å, plus Hα, over 28 nights in 2005. The light curves show intrinsic stellar variability due to star-spots with an amplitude in the blue band of 0.051 mag and a period of 4.847 d. In addition, three large flares were detected in the data which all occur near the minimum brightness of the star. We remove the intrinsic stellar variability and combine the light curves of all the filters in order to search for transits by possible planetary companions orbiting in the plane of the nearly edge-on debris disc. The combined final light curve has a sampling of 0.35 min and a standard deviation of 6.8 mmag. We performed Monte Carlo simulations by adding fake transits to the observed light curve and find with 95 per cent significance that there are no Jupiter mass planets orbiting in the plane of the debris disc on circular orbits with periods,   P ≤ 5  d. In addition, there are no young Neptune like planets (with radii 2.5 times smaller than the young Jupiter) on circular orbits with periods,   P ≤ 3  d.