Search Publications
Growth mechanisms and dune orientation on Titan
Lorenz, Ralph D.; Tokano, Tetsuya; Rodriguez, Sébastien +8 more
Dune fields on Titan cover more than 17% of the moon's surface, constituting the largest known surface reservoir of organics. Their confinement to the equatorial belt, shape, and eastward direction of propagation offer crucial information regarding both the wind regime and sediment supply. Herein, we present a comprehensive analysis of Titan's dun…
Surface of Ligeia Mare, Titan, from Cassini altimeter and radiometer analysis
Le Gall, Alice; Hayes, Alex; Zebker, Howard +3 more
Cassini radar observations of the surface of Ligeia Mare collected during the 23 May 2013 (T91) Cassini flyby show that it is extremely smooth, likely to be mostly methane in composition, and exhibits no surface wave activity. The radar parameters were tuned for nadir-looking geometry of liquid surfaces, using experience from Cassini's only compar…
Fast transport of resonant electrons in phase space due to nonlinear trapping by whistler waves
Krasnoselskikh, V.; Artemyev, A. V.; Agapitov, O. V. +4 more
We present an analytical, simplified formulation accounting for the fast transport of relativistic electrons in phase space due to wave-particle resonant interactions in the inhomogeneous magnetic field of Earth's radiation belts. We show that the usual description of the evolution of the particle velocity distribution based on the Fokker-Planck e…
Dynamic auroral storms on Saturn as observed by the Hubble Space Telescope
Brown, R. H.; Baines, K. H.; Dougherty, M. K. +14 more
We present observations of significant dynamics within two UV auroral storms observed on Saturn using the Hubble Space Telescope in April/May 2013. Specifically, we discuss bursts of auroral emission observed at the poleward boundary of a solar wind-induced auroral storm, propagating at ∼330% rigid corotation from near ∼01 h LT toward ∼08 h LT. We…
The long-term steady motion of Saturn's hexagon and the stability of its enclosed jet stream under seasonal changes
Hueso, R.; Sánchez-Lavega, A.; Rojas, J. F. +14 more
We investigate the long-term motion of Saturn's north pole hexagon and the structure of its associated eastward jet, using Cassini imaging science system and ground-based images from 2008 to 2014. We show that both are persistent features that have survived the long polar night, the jet profile remaining essentially unchanged. During those years, …
The flushing of Ligeia: Composition variations across Titan's seas in a simple hydrological model
Lorenz, Ralph D.
We use a simple box model to explore possible differences in the liquid composition of Titan's seas. Major variations in the abundance of involatile ethane, somewhat analogous to salinity in terrestrial waters, arise from the hydrological cycle, which introduces more "fresh" methane rainfall at the highest latitudes in summer. The observed composi…
Global model of low-frequency chorus (fLHR<f<0.1fce) from multiple satellite observations
Meredith, Nigel P.; Horne, Richard B.; Thorne, Richard M. +2 more
Whistler mode chorus is an important magnetospheric emission, playing a dual role in the acceleration and loss of relativistic electrons in the Earth's outer radiation belt. Chorus is typically generated in the equatorial region in the frequency range 0.1-0.8 fce, where fce is the local electron gyrofrequency. However, as the…
Cusp observation at Saturn's high-latitude magnetosphere by the Cassini spacecraft
Coates, A. J.; Krupp, N.; Dougherty, M. K. +11 more
We report on the first analysis of magnetospheric cusp observations at Saturn by multiple in situ instruments onboard the Cassini spacecraft. Using this we infer the process of reconnection was occurring at Saturn's magnetopause. This agrees with remote observations that showed the associated auroral signatures of reconnection. Cassini crossed the…
Highly structured electron anisotropy in collisionless reconnection exhausts
Torbert, R. B.; Li, G.; Chen, L. -J. +6 more
Results from two-dimensional particle-in-cell simulations of collisionless magnetic reconnection with zero guide field discussed in this paper reveal that around the time when the reconnection rate peaks, electron velocity distributions become highly structured in magnetic islands and open exhausts. Rings, arcs, and counterstreaming beams are gene…
Enhanced ionization of the Martian nightside ionosphere during solar energetic particle events
Gurnett, D. A.; Futaana, Y.; Němec, F. +2 more
Electron densities in the Martian nightside ionosphere are more than 90% of time too low to be detected by the Mars Advanced Radar for Subsurface and Ionosphere Sounding radar sounder on board the Mars Express spacecraft. However, the relative number of ionograms with peak electron density high enough to be detected represents a good statistical p…