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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2005.11.005 Byline: Renee Prange (a)(b), Thierry Fouchet (a)(c), Regis Courtin (a), J.E.P. Connerney (d), John C. McConnell (e) Keywords: Atmospheres; composition; Photochemistry; Saturn; atmosphere; Ultraviolet observations Abstract: We obtained spatially-resolved ultraviolet spectra of Saturn in 1994 with the Faint Object Spectrometer and Goddard High Resolution Spectrograph of the Hubble Space Telescope. We observed four areas on the planet at 15[degrees]aN, 33[degrees]aS, 41[degrees]aS, and 52[degrees]aS, with a field-of-view of less than 2x2 arcsec.sup.2, compared to the 16-arcsec planet diameter. The wavelength range, 1550-2300 A, encompasses absorption from major hydrocarbons (C.sub.2H.sub.6, C.sub.2H.sub.4, C.sub.2H.sub.2, CH.sub.3C.sub.2H, C.sub.4H.sub.2) and water. We find global hydrocarbon abundances and a C.sub.2H.sub.2 vertical distribution compatible with infrared observations, in contrast with previous analyses of ultraviolet spectra. The stratospheric haze opacity decreases from polar region to the equator. Saturn mid-latitudes are photochemically distinct from the rest of the planet. At 33[degrees]aS, the spectrum requires either (1) a distinctly different C.sub.2H.sub.2 vertical distribution or (2) a locally enhanced water abundance. At 41[degrees]aS, the hydrocarbon abundance exhibits a local minimum, within a global trend of increasing abundance from equator to pole. This global trend may result from an increased abundance of short-lived hydrocarbons such as C.sub.4H.sub.2. Photochemical models predict a depletion of hydrocarbon molecules in the presence of stratospheric water [Moses et al., 2000. Icarus 143, 166-202]. These results are consistent with a localized influx of water, in the form of high charge to mass ratio particles, flowing into Saturn's atmosphere at latitudes magnetically linked to the rings. Author Affiliation: (a) LESIA, Observatoire de Paris, 5 Place Jules Janssen, 92195 Meudon Cedex, France (b) Institut d'astrophysique spatiale, Universite Paris-Sud 11 and CNRS (UMR8617), BAcentstiment 121, F-91405 Orsay, France (c) AOPP, University of Oxford, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU, UK (d) Laboratory for Extraterrestrial Physics, Goddard Space Flight Center, Code 695, Greenbelt, MD 20771, USA (e) Department of Earth and Atmospheric Science, York University, Toronto, Canada M3J 1P3 Article History: Received 7 April 2005; Revised 31 October 2005

Mars currently has no global magnetic field of internal origin but must have had one in the past, when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like magnetic field (thermoremanent magnetization). A new map of the magnetic field of Mars, compiled by using measurements acquired at an [approximately equal to] 400-km mapping altitude by the Mars Global Surveyor spacecraft, is presented here. The increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the Mars crust. Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes and Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and support the notion that the Mars crust formed during an early era of plate tectonics. magnetic | planetary | plate tectonics

The distribution of H(sub 3)(super +) emissions in Jupiter's polar region is interpreted in terms of the corresponding source regions and the energetic in the magnetosphere by reference to corrected jovimagnetic coordinates based on the VIP4 magnetic field model of J. E. P. Connerney et al. (1998, J. Geophys. Res. 103,11929-11939). Two sets of 3.43-(mu)m auroral images, acquired on May 31/June 1,1996, and on July 8/July 9, 1996, using NSFCAM at NASA IRTF, were analyzed. Model images were generated for observed rotation phases, and the generalized inverse methodology of T. Satoh et al. (1996, Icarus 122, 1-23) is applied to pixel-by-pixel comparison of intensities to constrain the parameters of the emission source model. The most intense emissions are found between the 12-R(sub j) (jovian radii) and 30-R(sub j) ovals, representing the main auroral emissions. The System-III longitudes (lambda(sub III) of peak brightness in this zone, (lambda(sub III) approximately 260 degrees in the north and approximately 130 degrees in the south, coincide well with those of the minimum surface field magnitudes according to the VIP4 model. Between the 8-R(sub j) and the 12-R(sub j) ovals, the peak brightness occurs at (lambda(sub III) approximately 215 degrees in the north and at approximately 25 degrees in the south, consistent with the Satoh et al. (1996) System-III anomalies. These enhancements may originate from the 'windshield wiper' effects of drifting electrons, caused by pitch angle scattering of varying efficiency from the inner to the distant magnetosphere. The total power emitted from the entire auroral region by the H(sub 3)(super +) ion at all ro-vibrational levels is estimated as 2.1 x 10(super 12) W in the north, and 1.2 x 10(super 12) W in the south. Relative contributions from the individual zones are approximately 10% from the 6- to 8-R(sub j) zone, approximately 20% from the 8- to 12-R(sub j) zone, approximately 25% from the 12- to 30-R(sub j) zone, and approximately 45% from the polar-cap emission, respectively. Key Words: Jupiter, magnetosphere; aurorae; magnetic fields; ionospheres; infrared observations.

The magnetometer and electron reflectometer investigation (MAG/ER) on the Mars Global Surveyor spacecraft has obtained magnetic field and plasma observations throughout the near-Mars environment, from beyond the influence of Mars to just above the surface (at an altitude of ~100 kilometers). The solar wind interaction with Mars is in many ways similar to that at Venus and at an active comet, that is, primarily an ionospheric-atmospheric interaction. No significant planetary magnetic field of global scale has been detected to date ([is less than] 2 X [10.sup.21] Gauss-cubic centimeter), but here the discovery of multiple magnetic anomalies of small spatial scale in the crust of Mars is reported., The Mars Global Surveyor (MGS) magnetic field experiment is identical to that developed for the Mars Observer Mission that failed to achieve Mars orbit in 1993 (1). The instrumentation provides [...]

Far-ultraviolet images of Jupiter from the Hubble Space Telescope Wide Field Planetary Camera 2 reveal polar auroral emissions at 300 kilometer resolution and three times higher sensitivity than previously achieved. Persistent features include a main oval containing most of the emission and magnetically connected to the middle magnetosphere, diffuse and variable emissions poleward of the main oval, and discrete emission from Io's magnetic footprint equatorward of the oval. The auroral emissions are variable, exhibit magnetic conjugacy, and are visible above the planet limb. All emissions approximately co-rotate with Jupiter except the Io 'footprint,' which is fixed along Io's magnetic flux tube., The presence and approximate strength of Jupiter's magnetic field have been known since the 1954 detection of radio emissions from trapped charged particles (1). In 1964 the decametric emissions were [...]

A program of observations of Jupiter's [Mathematical Expression Omitted] auroras was conducted during the first 4 months of 1992, a period that spanned the Ulysses encounter. Daily variations of auroral intensity are small in magnitude ([approximately]20%) and well correlated with variations in the solar wind ram pressure arriving at Jupiter. A much larger (factor of 3) time variation is observed to occur on a time scale of approximately 2 months. During the first 2 months of observation, the inferred total intrinsic intensity of the northern aurora exceeded that of the southern aurora by a factor of 2. Throughout the latter 2 months, characterized by less intense auroral activity, the intensity of the northern aurora was comparable to that of the southern aurora.

The electrodynamic interaction between Io and the Jovian magnetosphere drives currents to and from the planet's ionosphere, where [H.sub.3.sup.+] emission is excited. Direct images of this phenomenon were obtained with the ProtoCAM infrared camera at the National Aeronautics and Space Administration's 3-m Infrared Telescope Facility. The emissions are localized to the instantaneous foot of the lo flux tube, [is nearly equal to] 8 ° equatorward of the mor intense auroral [H.sub.3.sup.+] emission associated with higher magnetic latitudes. The foot of the lo flux tube leads that of (undisturbed) model magnetic field lines passing through lo by 15 ° to 20 ° in longitude and is less visible in the northern hemisphere at longitudes where the surface magnetic field strength is greatest. These data favor the unipolar inductor model of the lo interaction and provide insight into the source location and generation of Jovian decameter radio emission., Radio emission from the Jovian magnetosphere was first detected in 1955[1] and has been monitored ever since by terrestrial observers and spacecraft[2]. In 1964, Bigg discovered that the observation of [...]

Magnetic fields measured by Voyager 1 show that the spacecraft crossed or was crossed by the termination shock on about 16 December 2004 at 94.0 astronomical units. An estimate of the compression ratio of the magnetic field strength B (± standard error of the mean) across the shock is [B.sub.2]/[B.sub.1] = 3.05 ± 0.04, but ratios in the range from 2 to 4 are admissible. The average B in the heliosheath from day I through day 110 of 2005 was 0.136 ± 0.035 nanoteslas, ~4.2 times that predicted by Parker's model for B. The magnetic field in the heliosheath from day 361 of 2004 through day 110 of 2005 was pointing away from the Sun along the Parker spiral. The probability distribution of hourly averages of B in the heliosheath is a Gaussian distribution. The cosmic ray intensity increased when B was relatively large in the heliosheath., The existence of a shock at which a stellar wind makes a transition from a relatively cool supersonic flow to a hot subsonic flow was suggested by Weymann (1). In [...]

Reports that the Mars Global surveyor spacecraft obtained vector magnetic field measurements above the surface of Mars. Organization of crustal magnetization linear features; Crustal remanent magnetization and terrestrial crust observations; Discovery of groups of quasi-parallel linear features of altering magnetic polarity; Comparison to magnetic features associated with sea floor spreading and crustal genesis on Earth; Suggestion of an era of plate tectonics on Mars.

Reports that vector magnetic field observations of the martian crust were acquired by the Mars Global Surveyor (MGS) magnetic field experiment/electron reflectometer (MAG/ER) during the aerobraking and science phasing orbits. Observations of magnetic field sources, strength and geometry; Correlation between the location of the sources and the ancient cratered terrain of the martian highlands; Implication of cessation of internal dynamo action during the early Naochian epoch; Other observations.

Abstract: Early in the history of planetary evolution portions of Martian crust became magnetized by dynamo-generated magnetic field. A lateral distribution of the secondary magnetic field generated by crustal remanent sources containing magnetic carriers of certain grain size and mineralogy is able to produce an ambient magnetic field of larger intensity than preexisting dynamo. This ambient field is capable of magnetizing portions of deeper crust that cools through its blocking temperatures in an absence of dynamo. We consider both magnetite (Fe3O4) and hematite (α-Fe2O3) as minerals contributing to the overall magnetization. Analysis of magnetization of magnetic minerals of various grain size and concentration reveals that magnetite grains less than 0.01mm in size, and hematite grains larger than 0.01mm in size can become effective magnetic source capable of magnetizing magnetic minerals contained in surrounding volume. Preexisting crustal remanence (for example ∼250A/m relates to 25% of multi-domain hematite) can trigger a self-magnetizing process that can continue in the absence of magnetic dynamo and continue strengthening and/or weakening magnetic anomalies on Mars. Thickness of the primary magnetic layer and concentration of magnetic carriers allow specification of the temperature gradient required to trigger a self-magnetization process. [Copyright &y& Elsevier]