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): 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): 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 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 17 December 2014 Source: Planetary and Space Science Author(s): A. Mahieux , A.C. Vandaele , S. Robert , V. Wilquet , R. Drummond , S. Chamberlain , D. Belyaev , J.L. Bertaux SOIR on board Venus Express sounds the Venus upper atmosphere using the solar occultation technique. It detects the signature from many Venus atmosphere species, including those of SO 2 and CO 2 . SO 2 has a weak absorption structure at 4 µm, from which number density profiles are regularly inferred. SO 2 volume mixing ratios (VMR) are calculated from the total number density that are also derived from the SOIR measurements. This work is an update of the previous work by Belyaev et al. (2012) , considering the SO 2 profiles on a broader altitude range, from 65 to 85 km. Positive detection VMR profiles are presented. In 68% of the occultation spectral datasets, SO 2 is detected. The SO 2 VMR profiles show a large variability up to two orders of magnitude, on a short term time scales. We present mean VMR profiles for various bins of latitudes, and study the latitudinal variations; the mean latitude variations are much smaller than the short term temporal variations. A permanent minimum showing a weak latitudinal structure is observed. Long term temporal trends are also considered and discussed. The trend observed by Marcq et al. (2013) is not observed in this dataset. Our results are compared to literature data and generally show a good agreement.

Description: Publication date: Available online 17 December 2014 Source: Planetary and Space Science Author(s): A. Mahieux , V. Wilquet , A.C. Vandaele , S. Robert , R. Drummond , S. Chamberlain , A. Grau Ribes , J.L. Bertaux The SOIR instrument on board Venus Express regularly sounds the Venus mesosphere using the solar occultation technique. Densities and volume mixing ratios of HCl and HF are measured in the 70 to 115 km and 75 to 110 km altitude region respectively, at the Venus terminator. All latitudes from pole to pole are covered. In this work, we study the latitude and long-term variations of the volume mixing ratio (VMR) of HCl, and the long-term time trend of HF, from June 2006 to February 2013. This period of time corresponds to approximately eleven Venusian years. Large variations in the VMR profiles are observed, mostly on the short-term. Both hydrogen halides present unforeseen positive exponential gradients of their VMR with pressure, which shows time and latitude variations. Long-term trends on the whole period of the HCl VMR are also observed at certain pressure levels in the equatorial and polar regions. HF also presents a time dependence of its VMR at certain pressure levels. Results are compared to previous HCl and HF VMR observations. The ability of SOIR to target both H 35 Cl and H 37 Cl isotopologues has also been investigated. Numerous concomitant density profiles lead to the determination of the 37 Cl/ 35 Cl isotopic ratio on Venus, found to be equal to 0.34±0.13, which is compatible with the value found on Earth.

Description: Publication date: Available online 16 December 2014 Source: Planetary and Space Science Author(s): K.T. Ramesh , James D. Hogan , Jamie Kimberley , Angela Stickle Modeling of catastrophic disruption requires understanding the processes of dynamic failure and fragmentation. This paper summarizes current mechanisms and models for dynamic failure, strength, and fragmentation, reviewing these from a mechanics perspective and with an emphasis on making links to the developing advances in these areas in the engineering and computational mechanics communities. We describe dynamic failure processes, examine size and rate effects, articulate the scaling concepts that arise naturally from these processes, and examine the influences of these processes on effective strength and fragmentation.

Description: Publication date: Available online 13 December 2014 Source: Planetary and Space Science Author(s): M.A. Ivanov , J.W. Head Two major types of volcanic units, older regional plains and younger lobate plains, make up ∼50% of the surface of Venus and represent different epochs of volcanism. The abundance of impact craters partially embayed from the exterior by each of these two types of units permits the testing of the key points of the model of equilibrium resurfacing. The proportion of craters embayed by the older regional plains is ∼3%, which requires the typical size of a volcanic resurfacing event to be ∼2700 km (∼25° of angular diameter) in the framework of the equilibrium model. These event dimensions are inconsistent with the quasi-random spatial distribution of the craters. The proportion of craters embayed by younger lobate plains is 33%, which can be achieved if the characteristic size of the resurfacing event is less than ∼160 km (∼1.5° of angular diameter). Events of this size do not disturb the character of the spatial distribution of craters. We conclude that the style of volcanic resurfacing on Venus has changed significantly during its observable portion of the geologic history. During the global volcanic regime when regional plains were emplaced, volcanism acted in large regions and the process of formation of regional plains was more intensive than accumulation of impact craters. This led to the very small proportion of embayed craters (∼3%). Later, during the network-rifting and volcanism regime (emplacement of lobate plains), volcanic sources were localized at distinctive centers, the net volcanic intensity decreased and became comparable to the rate of accumulation of craters, which resulted in much larger percentage (33%) of craters embayed by lobate plains.