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  • 1
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    Substorms At Jupiter: Galileo Observations of Transient Reconnection in The Near Tail (2000)
    In:  Other Sources
    Details
    Publication Date: 2011-08-23
    Description: The magnetic flux content of the Jovian magnetosphere is set by the internal dynamo, but those magnetic field lines are constantly being loaded by heavy ions at the orbit of lo and dragged inexorably outward by the centrifugal force. Vasyliunas has proposed a steady state reconnecting magnetospheric model that sheds plasma islands of zero net magnetic flux and returns nearly empty flux tubes to the inner magnetosphere. The Galileo observations indicate that beyond 40 Rj the current sheet begins to tear and beyond 50 Rj on the nightside explosively reconnects as the tearing site reaches the low density lobe region above and below the current sheet. Small events occur irregularly but on average about every 4 hours and large events about once a day. The magnetic flux reconnected in such events amounts up to about 70,000 Webers/sec and is sufficient to return the outwardly convected magnetic flux to the inner magnetosphere. Since this process releases plasmoids into the jovian tail, as do terrestrial substorms; since this process involves explosive reconnection across the current sheet on the nightside of the planet, as do terrestrial substorms; and since the process is a key in closing the circulation pattern of the magnetic and plasma flux, as it is in terrestrial substorms; we refer to these events as jovian substorms.
    Keywords: Astronomy
    Type: Advanced Space Research (ISSN 0273-1177); Volume 26; No. 10; 1499-1504
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  • 2
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    Characterization of Mineralogy Across Vesta (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: Dawn VIR spectra are characterized by pyroxene absorptions and no clear evidence for abundant other minerals are observed at the scale of the present measurements. Even though Vesta spectra are dominated by pyroxenes, spectral variation at regional and local scales are evident and distinct color units are identified. Although almost all of the surface materials exhibit spectra like those of howardites, some large units can be interpreted to be material richer in diogenite (based on pyroxenes band depths and band centers) and some others like eucrite-rich howardite units. VIR data strongly indicate that the south polar region (Rheasilvia) has its own spectral characteristics, indicating the presence of Mg-pyroxene-rich terrains (diogenite-like), while the equatorial areas have swallower band depths and average band centers at slightly longer wavelengths, consistent with more eucrite rich materials. Vesta surface shows considerable diversity at smaller scales (tens of km), in terms of spectral reflectance and emission, band depths and slopes. Many bright and dark spots are present on Vesta. Dark spots have low reflectance at visible wavelengths and are spectrally characterized by shallower 1 and 2 micron bands with respect the surrounding terrains. Bright materials have high reflectance and are often spectrally characterized by deep pyroxenes absorption bands. Vesta presents complex geology/topography and the mineral distribution is often correlated with geological and topographical structures. Ejecta from large craters have distinct spectral behaviors, and materials exposed in the craters show distinct spectra on floors and rims. VIR reveals the mineralogical variation of Vesta s crustal stratigraphy on local and global scales. Maps of spectral parameters show surface and subsurface unit compositions in their stratigraphic context. The hypothesis that Vesta is the HED parent body is consistent with, and strengthened by, the geologic and spectral context for pyroxene distribution provided by Dawn.
    Keywords: Geophysics
    Type: JSC-CN-25729 , European Geosciences Union General Assembly 2012; Apr 22, 2012 - Apr 27, 2012; Vienna; Austria
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  • 3
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    Colors and Photometry of Bright Materials on Vesta as Seen by the Dawn Framing Camera (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-19
    Description: The Dawn spacecraft has been in orbit around the asteroid Vesta since July, 2011. The on-board Framing Camera has acquired thousands of high-resolution images of the regolith-covered surface through one clear and seven narrow-band filters in the visible and near-IR wavelength range. It has observed bright and dark materials that have a range of reflectance that is unusually wide for an asteroid. Material brighter than average is predominantly found on crater walls, and in ejecta surrounding caters in the southern hemisphere. Most likely, the brightest material identified on the Vesta surface so far is located on the inside of a crater at 64.27deg S, 1.54deg . The apparent brightness of a regolith is influenced by factors such as particle size, mineralogical composition, and viewing geometry. As such, the presence of bright material can indicate differences in lithology and/or degree of space weathering. We retrieve the spectral and photometric properties of various bright terrains from false-color images acquired in the High Altitude Mapping Orbit (HAMO). We find that most bright material has a deeper 1-m pyroxene band than average. However, the aforementioned brightest material appears to have a 1-m band that is actually less deep, a result that awaits confirmation by the on-board VIR spectrometer. This site may harbor a class of material unique for Vesta. We discuss the implications of our spectral findings for the origin of bright materials.
    Keywords: Astronomy
    Type: JSC-CN-25735 , European Geosciences Union General Assembly 2012; Apr 22, 2012 - Apr 27, 2012; Vienna; Austria
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  • 4
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    Electromagnetic Ion Cyclotron Waves in the High-Altitude Cusp: Polar Observations (2005)
    In:  Other Sources
    Details
    Publication Date: 2019-07-18
    Description: High-resolution magnetic field data from the Polar Magnetic Field Experiment (MFE) show that narrow-band waves at frequencies approx. 0.2-3 Hz are a permanent feature in the vicinity of the polar cusp. The waves have been found in the magnetosphere adjacent to the cusp (both poleward and equatorward of the cusp) and in the cusp itself. The occurrence of waves is coincident with depression of magnetic field strength associated with enhanced plasma density, indicating the entry of magnetosheath plasma into the cusp region. The wave frequencies are generally scaled by the local proton cyclotron frequency and vary between 0.2 and 1.7 times local proton cyclotron frequency. This suggests that the waves are generated in the cusp region by the precipitating magnetosheath plasma. The properties of the waves are highly variable. The waves exhibit both left-handed and right-handed polarization in the spacecraft frame. The propagation angles vary from nearly parallel to nearly perpendicular to the magnetic field. We find no correlation among wave frequency, propagation angle, and polarization. Combined magnetic field and electric field data for the waves indicate that the energy flux of the waves is guided by the background magnetic field and points downward toward the ionosphere.
    Keywords: Geophysics
    Type: 2005 Chapman Conference on Magnetospheric ULF Waves; Mar 21, 2005 - Mar 25, 2005; San Diego, CA; United States
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  • 5
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    Dissipative Processes in the Magnetopause Boundary Layer and Flux Transfer Events Using the Interball Spacecraft (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Work on two quite distinct projects was accomplished: a study of flux transfer events and a study of the magnetosheath-polar cusp interface. The study with Oleg Vaisberg of the Space Research Institute in Moscow used only Interball data. We analyzed the magnetometer data and to assist the observations of Flux Transfer Events (FTEs) to aid in the interpretation of the data. One of the issues was to distinguish between simple traversals of the magnetopause and encounters with FTES. Once that distinction became clear then we could examine the changes in the plasma associated with the FTE. The second study was undertaken to study the turbulent interaction of the magnetosheath flow past the polar cusp. In this study Polar Data was used inside the magnetosphere as Interball crossed through the cusp into the magnetosheath. Our most interesting but least turbulent example was on May 29, 1996 when the interplanetary magnetic field (IMF) was northward. During these conditions the magnetosheath interface with the cusp becomes streamlined due to reconnection above the polar cusp. This reconnection provides a smooth surface across which the velocity shear occurs, thus minimizing turbulence in the interaction. The magnetopause current lies closer to the Earth than the flow boundary. This current layer reverses the field direction from nortward to southward in the neighborhood of the distant cusp and is somewhat noisty but not as much as this region becomes when the IMF is southward.
    Keywords: Geophysics
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  • 6
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    The CUSP/Magnetosheath Interface on May 29, 1996: Interball-1 and Polar Observations (1998)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: On May 29, 1996, under steady strong northward IMF and high solar wind dynamic pressure conditions both Polar and Interball cross field lines that pass through the northern cusp and apparently close to the post-cusp reconnection site. The magnetopause current observed by Interball consists of two quite distinct layers, an inner broad current that is quite turbulent and another current that is quite abrupt and quiet. Polar also crosses current layers, similar to the Interball inner one. These observations support a model in which cusp field lines experience essentially stochastic behavior but on average provide topological connection between the cusp and magnetosheath.
    Keywords: Geophysics
    Type: Paper-98GL01402 , Geophysical Research Letters (ISSN 0094-8534); 25; 15; 2963-2966
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  • 7
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    Design Study for a Global Magnetospheric Dynamics Mission (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: A successful design was developed, one with many advantages over the original mission. The time spent in orbit was more evenly spread over the region being investigated. The radiation close was significantly lower and the mission did not rely on gravity assist at the moon and thus did not have to make measurements that far out in the tail. A spacecraft design was developed that keeps interference from the engines to a minimum. The design however was quite specific for four spacecraft. It could not be easily scaled to five spacecraft for example. One problem was discovered that is a concern for all similar missions. Inter- spacecraft communication can determine the spacing of the vehicles easily and to the accuracy required. However, the orientation of the polyhedron with the spacecraft at its vertices is not well known for small separations. Ground station range measurements give the line of sight location well but not the angle around that vector. This is a problem any such mission needs to solve. Neither the navigation teams at Goddard nor at Lewis were willing to attempt to solve this problem. At the completion of the study a report was made to the AGU meeting in San Francisco and a paper published in the volume "Science Closure and Enabling Technologies for Constellation Class Missions". This paper is attached.
    Keywords: Geophysics
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  • 8
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    Solar Wind-Magnetosphere Coupling During an Isolated Substorm Event: A Multispacecraft ISTP Study (1997)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Multispacecraft data from the upstream solar wind, polar cusp, and inner magnetotail are used to show that the polar ionosphere responds within a few minutes to a southward IMF turning, whereas the inner tail signatures are visible within ten min from the southward turning. Comparison of two subsequent substorm onsets, one during southward and the other during northward IMF, demonstrates the dependence of the expansion phase characteristics on the external driving conditions. Both onsets are shown to have initiated in the midtail, with signatures in the inner tail and auroral oval following a few minutes later.
    Keywords: Geophysics
    Type: NASA-CR-205242 , Paper-97GL00816 , NAS 1.26:205242 , Geophysical Research Letters (ISSN 0094-8534); 24; 8; 983-986
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  • 9
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    Analysis of Temperature Maps of Selected Dawn Data Over the Surface of Vesta (2012)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The thermal behavior of areas of unusual albedo at the surface of Vesta can be related to physical properties that may provide some information about the origin of those materials. Dawn s Visible and Infrared Mapping Spectrometer (VIR) [1] hyperspectral cubes can be used to retrieve surface temperatures. Due to instrumental constraints, high accuracy is obtained only if temperatures are greater than 180 K. Bright and dark surface materials on Vesta are currently investigated by the Dawn team [e.g., 2 and 3 respectively]. Here we present temperature maps of several local-scale features that were observed by Dawn under different illumination conditions and different local solar times.
    Keywords: Geophysics
    Type: JSC-CN-25716 , 43rd Lunar and Planetary Science Conference; Mar 19, 2012 - Mar 23, 2012; The Woodlands, TX; United States
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  • 10
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    Mapping Vesta: First Results from Dawn's Survey Orbit (2011)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: The geologic objectives of the Dawn Mission [1] are to derive Vesta s shape, map the surface geology, understand the geological context and contribute to the determination of the asteroids origin and evolution. Geomorphology and distribution of surface features will provide evidence for impact cratering, tectonic activity, volcanism, and regolith processes. Spectral measurements of the surface will provide evidence of the compositional characteristics of geological units. Age information, as derived from crater size-frequency distributions, provides the stratigraphic context for the structural and compositional mapping results, thus revealing the geologic history of Vesta. We present here the first results of the Dawn mission from data collected during the approach to Vesta, and its first discrete orbit phase - the Survey Orbit, which lasts 21 days after the spacecraft had established a circular polar orbit at a radius of approx.3000 km with a beta angle of 10deg-15deg.
    Keywords: Geophysics
    Type: JSC-CN-23953 , EPSC-DPS Joint Meeting 2011; Oct 02, 2011 - Oct 07, 2011; Nantes; France
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