Excitation of whistler waves by reflected auroral electrons

Excitation of electron cyclotron waves and whistlers by reflected auroral electrons which possess a loss-cone distribution is investigated. Based on a given magnetic field and density model, the instability problem is studied over a broad region along the auroral field lines. This region covers altitudes ranging from one quarter of an Earth radius to five Earth radii. It is found that the growth rate is significant only in the region of low altitude, say below the source region of the auroral kilometric radiation. In the high altitude region the instability is insignificant either because of low refractive indices or because of small loss cone angles.     

Time-dependentX- andY-functions for an isotropically scattering neutron transport problem in a finite slab

Expressions for time-dependentX- andY-functions for a one-speed neutron transport problem in a finite slab have been derived using a technique combining invariant imbedding method and eigenfunction expansion method. The atmosphere has been considered to scatter isotropically.     

POLE-TO-POLE SOLAR WIND DENSITY FROM ULYSSES RADIO MEASUREMENTS

We present new in situ measurements of solar wind electron density as a function of heliolatitude. The data were obtained on Ulysses during its fast transit from south solar pole to north solar pole, at heliocentric distance about 1.5 AU, near the 1996 solar activity minimum. The density is measured accurately using the method of quasi-thermal noise spectroscopy with the Ulysses radio experiment, at a higher time resolution than the particle analysers on board. At low heliolatitudes (22° S to 21° N) the histogram of our data shows three main classes of flows with densities centered at 3.5, 7, and 12 cm^-3, close to the values previously found by near-ecliptic space probes, in the region where fast coronal hole wind alternates with slower streamer belt wind. Poleward of 22° latitude where Ulysses encountered fast wind coming from coronal holes, the histogram of our data shows a single class of flow centered at 2.9 cm^-3 with a roughly normal distribution. We find a density nearly independent of latitude, with the mean density from the south coronal hole 10% larger than that from the north, which may stem from a genuine north/south asymmetry and/or from the small decrease in solar activity during the time of the observations. We finally compare the data with some analytical models.     

The Maria asteroid family: Genetic relationships and a plausible source of mesosiderites near the 3:1 Kirkwood Gap

We present a mineralogical assessment of 12 Maria family asteroids, using near-infrared spectral data obtained over the years 2000-2009 combined with visible spectral data (when available) to cover the spectral interval of 0.4-2.5 μm. Our analysis indicates the Maria asteroid family, which is located adjacent to the chaotic region of the 3:1 Kirkwood Gap, appears to be a true genetic family composed of assemblages analogous to mesosiderite-type meteorites. Dynamical models by Farinella et al. (Farinella, P., Gunczi, R., Froeschlé, Ch., Froeschlé, C., [1993]. Icarus 101, 174-187) predict this region should supply meteoroids into Earth-crossing orbits. Thus, the Maria family is a plausible source of some or all of the mesosiderites in our meteorite collections. These individual asteroids were most likely once part of a larger parent object that was broken apart and dispersed. One of the Maria dynamical family members investigated, ((695) Bella), was found to be unrelated to the genetic Maria family members. The parameters of (695) Bella indicate an H-chondrite assemblage, and that Bella may be a sister or daughter of Asteroid (6) Hebe.     

The roughness of the dark side of Iapetus from the 2004 to 2005 flyby

The roughness of a planetary surface offers clues to its past geologic history. We apply a surface roughness model developed by Buratti and Veverka (Buratti, B.J., Veverka, J. [1985]. Icarus 64, 320-328) to Cassini ISS data from the January 1st, 2005 flyby of Iapetus. This model uses the observed scattering behavior to provide a depth to radius factor q quantifying the size of idealized craters on the surface. Our findings indicate that the surface on the dark side is significantly smoother than the surfaces of other icy low-albedo saturnian satellites. We have found that the average depth to radius on the leading (dark) side is 0.084, corresponding to a Hapke mean slope angle of 6°. As compared to the 13-33° Hapke mean slope angle of other icy satellites (Buratti, B.J., and 10 colleagues [2008]. Icarus 193, 309-322), our results present a clearly different picture for the leading surface of Iapetus, suggesting that the dark deposit contributes to the decrease in macroscopic surface roughness of the leading side. Attempts were made to obtain an average depth to radius value for the trailing (bright) side; however the scans of the bright side from this flyby exhibited large variations in albedo, resulting in results that were physically unrealistic.