Description: Publication date: Available online 30 December 2014 Source: Planetary and Space Science Author(s): Xiao-Ping Lu , Wing-Huen Ip Extended from the ellipsoid shape, cellinoid shape model consists of eight octants from eight different ellipsoids with the constraint that the adjacent octants have the same semi-axes in common. With the asymmetric shape, cellinoid shape model could be adopted in simulating the irregular shapes of asteroids. In this article, we attempt to apply cellinoid shape model to multiple light curves observed in various geometries and present some techniques to make the whole inverse process more efficient. Finally numerical experiments confirm that cellinoid shape model could derive the physical parameters of asteroids from both of synthetic and real light curves.

Description: Publication date: Available online 24 December 2014 Source: Planetary and Space Science Author(s): V.A. Parkhomov , A.V. Dmitriev , B. Tsegmed We examined the features of bursts of unstructured Pc1 geomagnetic pulsations recorded with period in the range T =2–5 s on 19 November 2007 using simultaneous observations by the geosynchronous satellites GOES-10, 11, 12, a constellation of high-apogee satellites THEMIS and by the CARISMA ground-based network of magnetometers. The pulsation excitation resulted from contact of an oblique interplanetary shock wave (ISW) with the magnetosphere. At geosynchronous orbit, we found eastward drift of the source of Pc1 bursts observed first by GOES-11 (~09 MLT), then by GOES-12 (~13 MLT) and, finally, by GOES-10 (~14 MLT). Ground-based observatories with ~40° longitudinal separation observed the excitation of oscillations with a delay to the west and east as compared with the median Fort Simpson observatory. An increase in frequency, seen at the sharp leading edge of oscillations, lasted for about 150 s. We determined the propagation velocity of the pulsations’ source from the difference between the first observations of the pulsations by the satellites and at the Earth. In order to interpret the observed patterns of pulsation we considered different mechanisms such as: 1) Eastward drifting clouds of energetic electrons accelerated due to compression of the magnetosphere; 2) Plasmaspheric bulges (or detached plasma); 3) Magnetopause surface waves generated in the region of contact with the ISW and resulting in undulation of the region of developing the cyclotron instability.

Description: Publication date: Available online 23 December 2014 Source: Planetary and Space Science Author(s): Smitha V. Thampi , R. Sridharan , Tirtha Pratim Das , S.M. Ahmed , J.A. Kamalakar , Anil Bhardwaj The measurements carried out by the Chandra's Altitudinal Composition Explorer (CHACE) onboard the Moon Impact Probe (MIP) of Chandrayaan I mission is used to obtain information on the 2-D distribution of the lunar atmospheric H 2 by a novel approach that makes use of the basic fact that the Moon has a Surface Boundary Exosphere (SBE).These are the ‘first’ daytime in situ measurements of lunar H 2 covering the 20°S to 88°S latitude region centered ~14°E longitude. A critical examination of the observed spatial features of the surface number density of H 2 vis-à-vis the surface topography delineated from the Lunar Laser Ranging Instrument (LLRI) in the main orbiter Chandrayaan –I, indicates that that lunar surface process may be important in introducing small scale variations in the H 2 number density. Another constituent which exhibited spatial variation in the observed partial pressure is 40 Ar and it was hypothesized that it is indicative of the spatial heterogeneity in the radiogenic activity of the Lunar interior ( Sridharan et al., 2013a ). The absolute number density at the surface and also the latitude/altitude variation of the densities that are reported for the first time, highlight the complexities of the sunlit lunar atmosphere.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): A. Kereszturi , I. Gyollai , M. Szabó Analyzing the alteration in an olivine chondrule of the NWA 2086 CV3 meteorite, infrared spectral, electron microprobe and optical microscopic observations were correlated to each other. The intensity and wavelength position of olivine peaks changed characteristically with the progression of alteration and related Fe/Mg substitution inward the chondrule. Moderate to good correlations were identified between Fo% composition and positions of 830 and 860 cm −1 IR peaks. The disappearance of 1020 cm −1 peak by structural change happens already at a low level alteration without changing the optical appearance of the mineral. The existence of the 980 cm −1 peak found to be an indicator of the intact phase of olivine. While profiles perpendicular to the chondrule's perimeter showed alteration progressed inward 15–20 μm distance without observable fractures (thus probable by some diffusion related process), the similar “alteration distance” from various obvious fractures inside the chondrule was only 3–5 μm distance. These observations suggest that the substitution was more effective close to the matrix, and also related to some fluids that although were able to circulate along the large internal fractures too, but did not produce such strong substitution there, like it happened close to the matrix. It was also demonstrated that the poorly exploited contact mode observations with ATR based reflection method in infrared spectroscopy provides a useful tool to analyze the alteration at micrometer scale without much sample preparation, and able to identify alteration already at such a low level where the olivines still look optically intact.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): Gina A. DiBraccio , James A. Slavin , Suzanne M. Imber , Daniel J. Gershman , Jim M. Raines , Caitriona M. Jackman , Scott A. Boardsen , Brian J. Anderson , Haje Korth , Thomas H. Zurbuchen , Ralph L. McNutt Jr. , Sean C. Solomon We report an investigation of magnetic reconnection in Mercury's magnetotail conducted with MESSENGER Magnetometer and Fast Imaging Plasma Spectrometer measurements during seven “hot seasons” when the periapsis of the spacecraft orbit is on Mercury's dayside. Flux ropes are formed in the cross-tail current sheet by reconnection. We have analyzed 49 flux ropes observed between 1.7 R M and 2.8 R M (where R M is Mercury's radius, or 2440 km) down the tail from the center of the planet, for which minimum variance analysis indicates that the spacecraft passed near the central axis of the structure. An average Alfvén speed of 465 km s −1 is measured in the plasma sheet surrounding these flux ropes. Under the assumption that the flux ropes moved at the local Alfvén speed, the mean duration of 0.74±0.15 s determined for these structures implies a typical diameter of ∼345 km, or ∼0.14 R M , which is comparable to a proton gyroradius in the plasma sheet of ∼380 km. We successfully fit the magnetic signatures of 16 flux ropes to a force-free model. The mean radius and core field determined in this manner were ∼450 km, or ∼0.18 R M , and ∼40 nT, respectively. A superposed epoch analysis of the magnetic field during these events shows variations similar to those observed at Earth, including the presence of a post-plasmoid plasma sheet, filled with disconnected magnetic flux, but the timescales are 40 times shorter at Mercury. The results of this flux rope survey indicate that intense magnetic reconnection occurs frequently in the cross-tail current layer of this small but extremely dynamic magnetosphere.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): R. Hueso , J. Peralta , I. Garate-Lopez , T.V. Bandos , A. Sánchez-Lavega The Venus Express mission has provided a long-term monitoring of Venus atmosphere including the morphology and motions of its upper clouds. Several works have focused on the dynamics of the upper cloud visible on the day-side in ultraviolet images sensitive to the 65–70 km altitude and in the lower cloud level (50 km height) observable in the night-side of the planet in the 1.74 μm spectral window. Here we use VIRTIS-M spectral images in nearby wavelengths to study the upper cloud layer in three channels: ultraviolet (360–400 nm), visible (570–680 nm) and near infrared (900–955 nm) extending in time the previous analysis of VIRTIS-M data. The ultraviolet images show relatively well contrasted cloud features at the cloud top. Cloud features in the visible and near infrared images lie a few kilometers below the upper cloud top, have very low contrast and are distinct to the features observed in the ultraviolet. Wind measurements were obtained on 118 orbits covering the Southern hemisphere over a six-year period and using a semi-automatic cloud correlation algorithm. Results for the upper cloud from VIRTIS-M ultraviolet data confirm previous analysis based on images obtained by the Venus Monitoring Camera ( Khatuntsev et al. (2013) . Icarus 226, 140–158). At the cloud top the mean zonal and meridional winds vary with local time accelerating towards the local afternoon. The upper branch of the Hadley cell circulation reaches maximum velocities at 45° latitude and local times of 14–16 h. The mean zonal winds in the ultraviolet cloud layer accelerated in the course of the 2006–2012 period at least 15 ms −1 . The near infrared and visible images show a more constant circulation without significant time variability or longitudinal variations. The meridional circulation is absent or slightly reversed in near infrared and visible images indicating that, either the Hadley-cell circulation in Venus atmosphere is shallow, or the returning branch of the meridional circulation extends to levels below the cloud level sensed in near infrared images. At subpolar to polar latitudes the three wavelength ranges show similar features and motions which is a signature of small vertical wind shear and may be affected by vertical convergence of both layers. At the clod top level observed in UV images there are signatures of a long-term acceleration of the zonal winds at afternoon hours when comparing zonal winds from the first years of Venus Express observations (2006–2008) to later dates (2009–2012) with a mean acceleration of zonal winds of 17±6 ms −1 between both time periods.

Description: Publication date: Available online 17 December 2014 Source: Planetary and Space Science Author(s): Thiago Statella This paper presents a review of geodetic and cartographic aspects involved in the mapping of Mars and in the handling of planetary data returned and available from different team missions. It focuses on the reference system adopted for the planet, the main coordinate systems being used and main projection systems adopted when representing the data in a map. Several returned data are available in two different coordinate systems, the planetographic and the planetocentric. Errors in latitude and longitude when taking one system for another are addressed and quantified. As an example, the difference between planetographic and planetocentric latitudes can reach up to ∼0.35°. Errors involving Equirectangular, Sinusoidal and Stereographic map projections, which are among the most common projections used to represent Mars data, are studied. Angular, linear and areal distortions are calculated for all three projections and the results are discussed. For the given examples, the maximum angular distortion and the distortion along parallels for a typical HiRISE image were ∼0.6° and ∼1.009, respectively. For the MOC image used in the examples, the maximum angular distortion and the distortion along meridians were ∼0.02° and ∼1.00000005, respectively. And for the Stereographic projection the distortion along meridians was ∼1.049150.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): M.L. Delitsky , K.H. Baines Observations by many spacecraft that have visited Venus over the last 40 years appear to confirm the presence of lightning storms in the Venus atmosphere. Recent observations by Venus Express indicate that lightning frequency and power is similar to that on Earth. While storms are occurring, energy deposition by lightning into Venus atmospheric constituents will immediately dissociate molecules into atoms, ions and plasma from the high temperatures in the lightning column (>30,000 K) and the associated shock waves and heating, after which these atom and ion fragments of C,O,S,N,H-containing molecules will recombine during cooldown to form new sets of molecules. Spark and discharge experiments in the literature suggest that lightning effects on the main atmospheric molecules CO 2 , N 2 , SO 2 , H 2 SO 4 and H 2 O will yield carbon oxides and suboxides (CO m , C n O m ), sulfur oxides (S n O, S n O m ), oxyge n (O 2 ), elemental sulfur (S n ), nitroge n oxides (NO, N 2 O, NO 2 ), sulfuric acid clusters (H n S m O x − .aH n S m O x e.g. HSO 4 − .mH 2 SO 4 ), polysulfur oxides, carbon soot and other exotic species. While the amounts generated in lightning storms would be much less than that derived from photochemistry, during storms these species can build up in a small area and so their local concentrations may increase significantly. For a storm of 100×100 km, the increase could be ~5 orders of magnitude if they remain in the storm region for a period before becoming well-mixed. Some of these molecular species may be detectable by instruments onboard Venus Express while they are concentrated in the storm regions. We explore the diversity of new products likely created in lightning storms on Venus.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): Y.J. Lee , D.V. Titov , N.I. Ignatiev , S. Tellmann , M. Pätzold , G. Piccioni The upper cloud layer of Venus is a key factor affecting radiative energy balance of the mesosphere. Observations of the temperature and the cloud top structure by Venus Express revealed their strong variability with latitude. We used the 1-D radiative transfer model to study the dependence of the radiative forcing on the cloud top structure. The cloud top altitude effectively controls outgoing thermal fluxes. Sharp cloud top boundary can produce a pronounced peak of both solar heating and thermal cooling that suggests a radiative origin of temperature inversions in the cold collar. Strong diurnal variation of net forcing at low latitudes can be responsible for the origin of convective cells observed in UV images. Latitudinal contrasts in the radiative forcing in the mesosphere can drive meridional Hadley-type circulation with meridional winds of few m/s and vertical motions with speed of few cm/s.

Description: Publication date: Available online 18 December 2014 Source: Planetary and Space Science Author(s): A. Piccialli , F. Montmessin , D. Belyaev , A. Mahieux , A. Fedorova , E. Marcq , J.-L. Bertaux , S. Tellmann , A.C. Vandaele , O. Korablev The thermal structure of Venus upper atmosphere (90–140 km) was investigated using stellar occultation measurements acquired by the SPICAV experiment on board Venus Express. The SPICAV ultraviolet channel provides CO 2 local density and temperature vertical profiles with a vertical resolution of 〈 7 km of both the southern and the northern hemispheres on the nightside (18:00-06:00 hr local time). A permanent layer of warm air is observed at the mesopause in the altitude range 90–100 km. Temperature then decreases with increasing altitude reaching a minimum value around 125 km. Spatial and temporal changes in the thermal structure have been analyzed. Local time variations dominate the structure of Venus atmosphere at these altitudes: temperatures show an increase of ∼ 20 K on the morning side compared to the evening side. The homopause altitude was also determined; it varies between 119 and 138 km of altitude, increasing from the evening side to the morning side. SPICAV temperature profiles were compared to several literature results from ground-based observations, previous spacecraft missions and the Venus Express mission.