Description: The nonlinear wave structure of arbitrary amplitude ion acoustic solitary waves (IASWs) are studied in the Sagdeev’s pseudopotential framework for an ultra-relativistic degenerate dense plasma comprising cold and hot electrons and inertial ultra-cold ions. By employing standard normal-mode analysis the dispersion relation for linear waves is studied. The numerical results are presented to understand the features of ion acoustic solitary wave structures. It is shown that the present plasma model supports IASWs having positive potential well. Also, it is found that the small amplitude rarefactive double layer solution can exist in such a plasma system in some parametric region. It is shown that solitary structures and double layers are affected by relevant plasma parameters.

Description: The absolute brightness of the zenith sky was measured using a simple calibrated spectrometer during the annular solar eclipse event on May 21, 2012 in Fujioka City, Japan (36.2924°N, 139.0823°E). The sensitivity of the spectrometer was calibrated as a function of wavelength between 400 and 700 nm with an integral sphere. The brightness of the sky decreased to 6 % of its usual condition at the maximum magnitude of the annular eclipse of 0.95 for all wavelengths. The curve describing the variation of sky brightness accords well with the total luminosity of the solar disk estimated by a simple model that accounts for the limb darkening effect. This study provides zenith sky radiance as a function of wavelength and solar elevation angle, which is useful for the investigation of new optical instruments for atmospheric studies.

Description: This paper deals with the existence of triangular points and their linear stability when the primaries are oblate spheroid and sources of radiation considering the effect of oblateness up to 10 −6 of main terms in the restricted three-body problem; we see that the locations of the triangular points are affected by the oblateness of the primaries and solar radiation pressure. It is further seen that these points are stable for 0 ≤  μ  ≤ μ c ; and unstable for μ c  ≤  μ  ≤1/2; where μ c is the critical mass value depending on terms which involve parameters that characterize the oblateness and radiation repulsive forces such that $ \mu_{c} \in (0,1/2) $ ; in addition to this an algorithm has been constructed to calculate the critical mass value.

Description: Magnetic field intensity of the horizontal component (H) data measured from Magnetic Data Acquisition System (MAGDAS) at Ilorin (geographic latitude: 8.47°N, geographic longitude: 4.68°E, geomagnetic latitude: 1.82°S, geomagnetic longitude: 78.6°S), Nigeria in the year 2009 (a low activity year) was used to study the diurnal, monthly-median and standard deviation of the solar quiet of the horizontal component ( S q H ). The diurnal variation of S q H and its corresponding monthly median variation ( MS q H ) shows minima values at pre-sunrise hours between 0500 and 0600 LT. The S q H value shows a daytime maximum variation range between 20 and 91 nT and a nighttime minimum variation range from 1 to 4 nT. The occurrences of daytime maxima of the S q H values that were observed in all the months are between the hours of 1000 and 1200 LT. The daytime maximum of the MS q H values from the entire months were seen at 1100 LT with exceptions of January and December. The month of October has the highest value (61 nT) and the lowest value was observed in December (35 nT). It is clearer that the range in maximums of S q H and MS q H variations during the daytime period in all the months is greater than the range in minimums observed at nighttime period (post-sunset and pre-sunrise). The monthly standard deviation (STD) depicts the index of variability of all the day-to-day variations in each month. Counter electrojet (CEJ) events were observed in the morning and as well during the evening hours. The magnitudes and frequencies of CEJ events during the evening hours are greater than that of the morning hours. CEJ seen during the morning period around 0500–0600 LT is the consequence of late reversals of nighttime westward currents to daytime eastward currents. A semi-annual variation with peak values during March, April, September and October was observed. Seasonal variation that was characterized with CEJ was also investigated.

Description: Pitch-angle diffusion coefficients of electrons have been calculated for resonant interaction with electrostatic electron-cyclotron harmonic (ECH) waves using quasi linear diffusion theory. Calculations have been performed for the planets Earth and Jupiter at three radial distances for each planet. Electron precipitation fluxes have also been calculated and compared with observed fluxes. At Earth, electrons of energy ≤200 eV may be put on strong diffusion at L = 10. At lower L values, observed ECH wave amplitudes are insufficient to put electrons on strong diffusion. At Jupiter, electrons can be put on strong diffusion at all L values. However, the energy of electrons which may be put on strong diffusion decreases from about 1 keV at L = 7 to ~100 eV at L = 17. It is concluded that ECH waves may be partly responsible for diffuse auroral precipitation of low energy electrons at Jupiter for lower L values. At Earth contribution of ECH waves to diffuse aurora is quite small.

Description: The use of lithosphere strength indicators (as for example the effective elastic thickness of the lithosphere or the depth to the brittle-ductile transition) can give clues on the surface heat flow and the thermal state of the ice crust of icy satellites, which in turn has profound implications for the internal evolution, and the possible existence of internal oceans, in these planetary bodies. As shown in this review, this kind of approach has found very high (and possibly recent) surface heat flows for Europa and ancient high heat flows for Ganymede. On the other hand, the heavily cratered of Callisto suggests a cold and inactive outer ice shell throughout the entire history of that body. However, irrespective of the greatly different geology recorded on the surface of the icy Galilean satellites, there is evidence from orbital magnetic observations for internal oceans in all them. By considering heat flow estimates in the context existence of internal oceans, a more complete description of the thermal history of the icy Galilean satellites should emerge.

Description: This article provides some astronomical background for a systematic study of the lunar regolith. The Moon, like other atmosphere-less bodies, is the subject to all kinds of cosmic radiation, which are imprinted in the lunar surface. Therefore, the study of the lunar regolith for signs of cosmic radiation can assist to trace the history of changes in these emissions over time. Mostly changes in the solar wind and galactic cosmic rays are very interesting at time intervals from a few tens of millions of years to several billion years. The paper develops the idea of paleoregolith, the possible location of which can be seen on the slopes of some craters (Euler, Bessel) in images obtained by camera of LRO spacecraft (LROC). Because of the complexities of placing a spacecraft on the slopes of craters, some other possible locations of paleoregolith are offered to consideration. To study the recent history of the evolution of the Moon and the inner planets (up to 200 million years) the stored information in impact and volcanic melts, which are widely represented in the LROC images, should be considered.

Description: As the number of observatories located on the surface of Earth is increasing largely in decades more and more photometric data of asteroids is observed to make the research about their various physical and chemical characteristics. Compared with hundreds of thousands of asteroids found up to now, rare hundreds of three-dimensional shape models of asteroids have been built from the tremendous photometric data with incessant observations, i.e. lightcurves. For some specific asteroid already with many observed lightcurves, the unceasing observation is not too much valuable, nevertheless an additional lightcurve observed in a request viewing aspect can refine the shape model and other related parameters. This article taking the asteroid (6) HEBE for example, attempts to introduce a method to make the observation plan by combining the request of the shape model and the orbital limitation of asteroids. Through analyzing the distribution of lightcurves of (6) HEBE, small cabins without any lightcurve data are found, which can be filled by new observations at some specified dates when the positions of Asteroid, Sun, Earth are limited as the request geometry.

Description: This paper analyzes Robe’s circular restricted three-body problem when the hydrostatic equilibrium figure of the first primary is assumed to be an oblate spheroid, the shape of the second primary is considered as a triaxial rigid body, and the full buoyancy force of the fluid is taken into account. It is found that there is an equilibrium point near the center of the first primary, another equilibrium point exists on the line joining the centers of the primaries and there exist infinite number of equilibrium points on an ellipse in the orbital plane of the second primary. It is also observed that under certain conditions, all these equilibrium points can be stable. The most interesting and distinguishable results of this study are the existence of elliptical points and their stability.

Description: A numerical simulation of the Oort cloud is used to explain the observed orbital distributions and numbers of Jupiter-family (JF) and Halley-type (HT) short-period (SP) comets. Comets are given initial orbits with perihelion distances between 5 and 36 au, and evolve under planetary, stellar and Galactic perturbations for 4.5 Gyr. This process leads to the formation of an Oort cloud (which we define as the region of semimajor axes a  〉 1,000 au), and to a flux of cometary bodies from the Oort cloud returning to the planetary region at the present epoch. The results are consistent with the dynamical characteristics of SP comets and other observed cometary populations: the near-parabolic flux, Centaurs, and high-eccentricity trans-Neptunian objects. To achieve this consistency with observations, the model requires that the number of comets versus initial perihelion distance is concentrated towards the outer planetary region. Moreover, the mean physical lifetime of observable comets in the inner planetary region ( q  〈 2.5 au) at the present epoch should be an increasing function of the comets’ initial perihelion distances. Virtually all observed HT comets and nearly half of observed JF comets come from the Oort cloud, and initially (4.5 Gyr ago) from orbits concentrated near the outer planetary region. Comets that have been in the Oort cloud also return to the Centaur (5 〈  q  〈 28 au, a  〈 1,000 au) and near-Neptune high-eccentricity regions. Such objects with perihelia near Neptune are hard to discover, but Centaurs with characteristics predicted by the model (e.g. large semimajor axes, above 60 au, or high inclinations, above 40°) are increasingly being found by observers. The model provides a unified picture for the origin of JF and HT comets. It predicts that the mean physical lifetime of all comets in the region q  〈 1.5 au is less than ∼200 revolutions.