D. G. Simpson

Preliminary interpretation of Titan plasma interaction as observed by the Cassini Plasma Spectrometer: Comparisons with Voyager 1

The Cassini Plasma Spectrometer (CAPS) instrument made measurements of Titan s plasma environment when the Cassini Orbiter flew through the moon s plasma wake October 26,2004 (flyby TA) and December 13,2004 (flyby TB). Preliminary CAPS ion and electron measurements from these encounters (1,2) are compared with measurements made by the Voyager I Plasma Science Instrument (PLS). The comparisons are used to evaluate previous interpretations and predictions of the Titan plasma environment that have been made using PLS measurements (3,4). The plasma wake trajectories of flybys TA, TB and Voyager 1 are similar because they occurred when Titan was near Saturn s local noon. These similarities make possible direct, meaningful comparisons between the various plasma wake measurements. The inquiries stimulated by the previous interpretations and predictions made using PLS data have produced the following results from the CAPS ion measurements: A) The major ambient ion components of Saturn s rotating magnetosphere in the vicinity of Titan are H+, H2+, and O+. B) Finite gyroradius effects are apparent in ambient 0 as the result of its interaction with Titan s atmosphere. C) The principal pickup ions are composed of H+, H2+, CH4+ and N2+. D) There is clear evidence of slowing down of the ambient plasma due to pickup ion mass loading; and, as the ionopause~ is approached, heavier pickup ions such as N2+ become dominant. The similarities and differences between the magnitudes and structures of the electron densities and temperatures along the three flyby trajectories are described

An unexplained 10–40° shift in the location of some diverse neutral atom data at 1 AU

Abstract Four different data sets pertaining to the neutral atom environment at 1 AU are presented and discussed. These data sets include neutral solar wind and interstellar neutral atom data from IMAGE/LENA, energetic hydrogen atom data from SOHO/HSTOF and plasma wave data from the magnetometer on ISEE-3. Surprisingly, these data sets are centered between 262° and 292° ecliptic longitude, ∼10–40° from the upstream interstellar neutral (ISN) flow direction at 254° resulting from the motion of the Sun relative to the local interstellar cloud (LIC). Some possible explanations for this offset, none of which is completely satisfactory, are discussed.

Jovian plasma torus interaction with Europa. Plasma wake structure and effect of inductive magnetic field: 3D hybrid kinetic simulation

Abstract The hybrid kinetic model supports comprehensive simulation of the interaction between different spatial and energetic elements of the Europa moon–magnetosphere system with respect to a variable upstream magnetic field and flux or density distributions of plasma and energetic ions, electrons, and neutral atoms. This capability is critical for improving the interpretation of the existing Europa flyby measurements from the Galileo Orbiter mission, and for planning flyby and orbital measurements (including the surface and atmospheric compositions) for future missions. The simulations are based on recent models of the atmosphere of Europa ( Cassidy et al., 2007 , Shematovich et al., 2005 ). In contrast to previous approaches with MHD simulations, the hybrid model allows us to fully take into account the finite gyroradius effect and electron pressure, and to correctly estimate the ion velocity distribution and the fluxes along the magnetic field (assuming an initial Maxwellian velocity distribution for upstream background ions). Photoionization, electron-impact ionization, charge exchange and collisions between the ions and neutrals are also included in our model. We consider the models with O ++ and S ++ background plasma, and various betas for background ions and electrons, and pickup electrons. The majority of O2 atmosphere is thermal with an extended non-thermal population ( Cassidy et al., 2007 ). In this paper, we discuss two tasks: (1) the plasma wake structure dependence on the parameters of the upstream plasma and Europas atmosphere (model I, cases (a) and (b) with a homogeneous Jovian magnetosphere field, an inductive magnetic dipole and high oceanic shell conductivity); and (2) estimation of the possible effect of an induced magnetic field arising from oceanic shell conductivity. This effect was estimated based on the difference between the observed and modeled magnetic fields (model II, case (c) with an inhomogeneous Jovian magnetosphere field, an inductive magnetic dipole and low oceanic shell conductivity).

Possible Origin of the Secondary Stream of Neutral Fluxes at 1 AU

The existence of a secondary stream of neutral atoms inside the heliosphere arriving from about 285° ecliptic longitude, which is about 30° higher than the nominal upstream direction of the inflowing interstellar gas, has been proposed recently based on a wide variety of observations from many different missions. We will discuss the LENA/IMAGE measurements in detail and conclude that the secondary stream is composed mainly of hydrogen atoms at an energy of about 1 keV. We will discuss some possible explanations for the origin of the secondary stream, with the most likely source being the region upstream of the termination shock.

NASA Computational Case Study: Modeling Planetary Magnetic and Gravitational Fields

In this case study, we model a planets magnetic and gravitational fields using spherical harmonic functions. As an exercise, we analyze data on the Earths magnetic field collected by NASAs MAGSAT spacecraft, and use it to derive a simple magnetic field model based on these spherical harmonic functions. The Web extra contains an ASCII text file of Magsat data, as mentioned in the article.

NASA Computational Case Study: The Flight of Friendship 7

In this case study, we study a method for computing the position of an Earth-orbiting spacecraft as a function of time. As an exercise, we compute the position of John Glenns Mercury spacecraft Friendship 7 as it orbited the Earth during the third flight of NASAs Mercury program.