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Gary S.P.,Space Science Institute Boulder | Fu X.,New Mexico Consortium Los Alamos | Cowee M.M.,Los Alamos National Laboratory | Winske D.,Los Alamos National Laboratory | Liu K.,Auburn University
Journal of Geophysical Research: Space Physics | Year: 2017

The Alfvén-cyclotron instability is driven by an ion temperature anisotropy such that T⊥/T|| >1 where ⊥ and || denote directions perpendicular and parallel to a uniform background magnetic field Bo, respectively. The computations presented here consider a model of a magnetized, homogeneous, collisionless plasma. Two representations of the proton velocity distribution are considered: a single bi-Maxwellian and a magnetospheric-like configuration of two components, a more dense, relatively cool, isotropic component and a less dense, relatively hot, bi-Maxwellian component which drives the instability. Only wave propagation parallel to Bo is considered. Using numerical solutions of the full kinetic linear dispersion equation, concise analytic expressions for the scaling of the dimensionless maximum instability growth rate and the corresponding dimensionless real frequency are derived as functions of three dimensionless variables: the hot proton temperature anisotropy, the relative hot proton density, and the hot proton β||. Furthermore, using one-dimensional hybrid particle-in-cell simulations of this same instability, a third relation for the scaling of the maximum amplitude of the dimensionless fluctuating magnetic field energy density is derived. ©2017. American Geophysical Union.

Mangold N.,University of Nantes | Forni O.,CNRS Institute for research in astrophysics and planetology | Dromart G.,University of Lyon | Stack K.,California Institute of Technology | And 43 more authors.
Journal of Geophysical Research E: Planets | Year: 2015

The Yellowknife Bay formation represents a ~5m thick stratigraphic section of lithified fluvial and lacustrine sediments analyzed by the Curiosity rover in Gale crater, Mars. Previous works have mainly focused on the mudstones that were drilled by the rover at two locations. The present study focuses on the sedimentary rocks stratigraphically above the mudstones by studying their chemical variations in parallel with rock textures. Results show that differences in composition correlate with textures and both manifest subtle but significant variations through the stratigraphic column. Though the chemistry of the sediments does not vary much in the lower part of the stratigraphy, the variations in alkali elements indicate variations in the source material and/or physical sorting, as shown by the identification of alkali feldspars. The sandstones contain similar relative proportions of hydrogen to the mudstones below, suggesting the presence of hydrous minerals that may have contributed to their cementation. Slight variations in magnesium correlate with changes in textures suggesting that diagenesis through cementation and dissolution modified the initial rock composition and texture simultaneously. The upper part of the stratigraphy (~1m thick) displays rocks with different compositions suggesting a strong change in the depositional system. The presence of float rocks with similar compositions found along the rover traverse suggests that some of these outcrops extend further away in the nearby hummocky plains. ©2015. American Geophysical Union.

Lanza N.L.,Los Alamos National Laboratory | Wiens R.C.,Los Alamos National Laboratory | Arvidson R.E.,Washington University in St. Louis | Clark B.C.,Space Science Institute Boulder | And 40 more authors.
Geophysical Research Letters | Year: 2016

The Curiosity rover observed high Mn abundances (>25wt % MnO) in fracture-filling materials that crosscut sandstones in the Kimberley region of Gale crater, Mars. The correlation between Mn and trace metal abundances plus the lack of correlation between Mn and elements such as S, Cl, and C, reveals that these deposits are Mn oxides rather than evaporites or other salts. On Earth, environments that concentrate Mn and deposit Mn minerals require water and highly oxidizing conditions; hence, these findings suggest that similar processes occurred on Mars. Based on the strong association between Mn-oxide deposition and evolving atmospheric dioxygen levels on Earth, the presence of these Mn phases on Mars suggests that there was more abundant molecular oxygen within the atmosphere and some groundwaters of ancient Mars than in the present day. ©2016. American Geophysical Union.

Arvidson R.E.,University of Missouri | Bell J.F.,Arizona State University | Catalano J.G.,University of Missouri | Clark B.C.,Space Science Institute Boulder | And 16 more authors.
Journal of Geophysical Research E: Planets | Year: 2015

Compact Reconnaissance Imaging Spectrometer for Mars hyperspectral (1.0-2.65μm) along-track oversampled observations covering Victoria, Santa Maria, Endeavour, and Ada craters were processed to 6m/pixel and used in combination with Opportunity observations to detect and map hydrated Mg and Ca sulfate minerals in the Burns formation. The strongest spectral absorption features were found to be associated with outcrops that are relatively young and fresh (Ada) or preferentially scoured of dust, soil, and coatings by prevailing winds. At Victoria and Santa Maria, the scoured areas are on the southeastern rims and walls, opposite to the sides where wind-blown sands extend out of the craters. At Endeavour, the deepest absorptions are in Botany Bay, a subdued and buried rim segment that exhibits high thermal inertias, extensive outcrops, and is interpreted to be a region of enhanced wind scour extending up and out of the crater. Ada, Victoria, and Santa Maria outcrops expose the upper portion of the preserved Burns formation and show spectral evidence for the presence of kieserite. In contrast, gypsum is pervasive spectrally in the Botany Bay exposures. Gypsum, a relatively insoluble evaporative mineral, is interpreted to have formed close to the contact with the Noachian crust as rising groundwaters brought brines close to and onto the surface, either as a direct precipitate or during later diagenesis. The presence of kieserite at the top of the section is hypothesized to reflect precipitation from evaporatively concentrated brines or dehydration of polyhydrated sulfates, in both scenarios as the aqueous environment evolved to very arid conditions. ©2015. American Geophysical Union.

Liu Y.,Southwest Research Institute | Glotch T.D.,State University of New York at Stony Brook | Scudder N.A.,Purdue University | Kraner M.L.,University of Nevada, Reno | And 5 more authors.
Journal of Geophysical Research E: Planets | Year: 2016

We present spectral unmixing results over the southwest Melas Chasma region, where a variety of hydrated minerals were identified. We use the Discrete Ordinate Radiative Transfer radiative transfer model to simultaneously model Mars atmospheric gases, aerosols, and surface scattering and retrieve the single-scattering albedos (SSAs) modeled by the Hapke bidirectional scattering function from Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) data. We employ a spectral unmixing algorithm to quantitatively analyze the mineral abundances by modeling the atmospherically corrected CRISM SSAs using a nonnegative least squares linear deconvolution algorithm. To build the spectral library used for spectral unmixing, we use the factor analysis and target transformation technique to recover spectral end-members within the CRISM scenes. We investigate several distinct geologic units, including an interbedded polyhydrated and monohydrated sulfate unit (interbedded unit 1) and an interbedded phyllosilicate-sulfate unit (interbedded unit 2). Our spectral unmixing results indicate that polyhydrated sulfates in the interbedded unit 1 have a much lower abundance (~10%) than that of the surrounding unit (~20%) and thus may have been partially dehydrated into kieserite to form the interbedded strata, supporting a two-staged precipitation-dehydration formation hypothesis. In the interbedded unit 2 phyllosilicates have an abundance of ~40% and are interbedded with ~20% sulfates. The results, in combination with thermodynamic calculations performed previously, suggest that the interbedded phyllosilicates and sulfates likely formed through coupled basalt weathering and evaporation. The methodology developed in this study provides a powerful tool to derive the mineral abundances, aiming to better constrain the formation processes of minerals and past aqueous environment on Mars. © 2016. American Geophysical Union. All Rights Reserved.

Lanza N.L.,Los Alamos National Laboratory | Fischer W.W.,California Institute of Technology | Wiens R.C.,Los Alamos National Laboratory | Grotzinger J.,California Institute of Technology | And 17 more authors.
Geophysical Research Letters | Year: 2014

The surface of Mars has long been considered a relatively oxidizing environment, an idea supported by the abundance of ferric iron phases observed there. However, compared to iron, manganese is sensitive only to high redox potential oxidants, and when concentrated in rocks, it provides a more specific redox indicator of aqueous environments. Observations from the ChemCam instrument on the Curiosity rover indicate abundances of manganese in and on some rock targets that are 1-2 orders of magnitude higher than previously observed on Mars, suggesting the presence of an as-yet unidentified manganese-rich phase. These results show that the Martian surface has at some point in time hosted much more highly oxidizing conditions than has previously been recognized. ©2014. American Geophysical Union.

Hartley D.P.,Lancaster University | Chen Y.,Los Alamos National Laboratory | Kletzing C.A.,University of Iowa | Denton M.H.,Space Science Institute Boulder | Kurth W.S.,University of Iowa
Journal of Geophysical Research A: Space Physics | Year: 2015

Most theoretical wave models require the power in the wave magnetic field in order to determine the effect of chorus waves on radiation belt electrons. However, researchers typically use the cold plasma dispersion relation to approximate the magnetic wave power when only electric field data are available. In this study, the validity of using the cold plasma dispersion relation in this context is tested using Electric and Magnetic Field Instrument Suite and Integrated Science (EMFISIS) observations of both the electric and magnetic spectral intensities in the chorus wave band (0.1-0.9 fce). Results from this study indicate that the calculated wave intensity is least accurate during periods of enhanced wave activity. For observed wave intensities >10-3 nT2, using the cold plasma dispersion relation results in an underestimate of the wave intensity by a factor of 2 or greater 56% of the time over the full chorus wave band, 60% of the time for lower band chorus, and 59% of the time for upper band chorus. Hence, during active periods, empirical chorus wave models that are reliant on the cold plasma dispersion relation will underestimate chorus wave intensities to a significant degree, thus causing questionable calculation of wave-particle resonance effects on MeV electrons. ©2015. The Authors.

Borovsky J.E.,University of Michigan | Denton M.H.,Space Science Institute Boulder
Journal of Geophysical Research A: Space Physics | Year: 2016

The trailing-edge rarefactions of 54 high-speed streams at 1AU are analyzed. The temporal durations of the trailing-edge rarefactions agree with ballistic calculations based on the observed speeds of the fast and slow wind bounding the rarefactions. A methodology is developed to measure solar-wind compression and rarefaction using the orientations of solar-wind current sheets. One focus is to determine the signature that best describes the location of the trailing-edge stream interface between coronal-hole-origin plasma and streamer-belt-origin plasma; based on the current-sheet orientations, on the magnetic-field strength, on the intensity of the electron strahl, and on the intensity of the negative vorticity, an inflection point in the temporal profile of the solar-wind velocity is taken as the best indicator of the trailing-edge stream interface. Computer simulations support this choice. Using superposed-epoch analysis, the plasma properties and turbulence properties of trailing-edge rarefactions are surveyed. Whereas the signatures of the coronal-hole/streamer-belt (slow-wind/fast-wind) boundary in the leading edge (corotating interaction region) stream interface are simultaneous, they are not simultaneous in the trailing edge, with ion-charge-state signatures occurring on average 13.7h prior to the proton entropy signature. It is suggested that differences in the leading and trailing edges of coronal holes on the Sun might account for the differences in the leading and trailing edges of high-speed streams at 1AU: the formation timescales, heating timescales, and charge-state-equilibration timescales of closed flux loops in the corona might be involved. © 2016. American Geophysical Union. All Rights Reserved.

Min K.,Auburn University | Liu K.,Auburn University | Gary S.P.,Space Science Institute Boulder
Journal of Geophysical Research A: Space Physics | Year: 2016

A ring-like proton velocity distribution with ∂fp(v⊥)/∂v⊥>0 and which is sufficiently anisotropic can excite two distinct types of growing modes in the inner magnetosphere: ion Bernstein instabilities with multiple ion cyclotron harmonics and quasi-perpendicular propagation and an Alfvén-cyclotron instability at frequencies below the proton cyclotron frequency and quasi-parallel propagation. Recent particle-in-cell simulations have demonstrated that even if the maximum linear growth rate of the latter instability is smaller than the corresponding growth of the former instability, the saturation levels of the fluctuating magnetic fields can be greater for the Alfvén-cyclotron instability than for the ion Bernstein instabilities. In this study, linear dispersion theory and two-dimensional particle-in-cell simulations are used to examine scalings of the linear growth rate and saturation level of the two types of growing modes as functions of the temperature anisotropy T⊥/T|| for a general ring-like proton distribution with a fixed ring speed of 2vA, where vA is the Alfvén speed. For the proton distribution parameters chosen, the maximum linear theory growth rate of the Alfvén-cyclotron waves is smaller than that of the fastest-growing Bernstein mode for the wide range of anisotropies (1≤T⊥/T||≤7) considered here. Yet the corresponding particle-in-cell simulations yield a higher saturation level of the fluctuating magnetic fields for the Alfvén-cyclotron instability than for the Bernstein modes as long as T⊥/T||≳3. Since fast magnetosonic waves with ion Bernstein instability properties observed in the magnetosphere are often not accompanied by electromagnetic ion cyclotron waves, the results of the present study indicate that the ring-like proton distributions responsible for the excitation of these fast magnetosonic waves should not be very anisotropic. © 2016. American Geophysical Union. All Rights Reserved.

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