Editorial to the Topical Collection: Role of Sample Return in Addressing Major Questions in Planetary Sciences

Space Science Reviews - Spectral retrieval has long been a powerful tool for interpreting planetary remote sensing observations. Flexible, parameterised, agnostic models are coupled with inversion...     

Mesospheric OH temperatures: Simultaneous ground-based and SABER OH measurements over Millstone Hill

We present rotational temperature measurements of the mesospheric OH emission layer using a meridional imaging spectrograph at Millstone Hill (42.6°N, 72.5°W). The system is equipped with a state-of-the-art bare-CCD detector and can yield simultaneous quasi-meridional images of the mesospheric OH and O₂ intensity and temperature fields at 87 and 94 km altitude during the course of each night. A cross-validation study of the rotational OH temperature measurements obtained on 61 nights during the autumnal months of 2005–2007 was undertaken with near-simultaneous kinetic temperature measurements made by the SABER instrument aboard the NASA TIMED satellite during overpasses of Millstone Hill. Excellent agreement was obtained between the two datasets with the small differences being attributable to differences in the spatial and temporal averaging inherent between the two datasets.     

HYDRODYNAMIC AND MHD EQUATIONS ACROSS THE BOW SHOCK AND ALONG THE SURFACES OF PLANETARY OBSTACLES

Examinations of the magnetohydrodynamic (MHD) equations across a bow shock are presented. These equations are written in the familiar Rankine–Hugoniot set, and an exact solution to this set is given which involves the upstream magnetosonic Mach number, plasma , polytropic index, and _B-v , as a function of position along the shock surface. The asymptotic Mach cone angle of the shock surface is also given as a function of the upstream parameters, as a set of transcendental equations. The standoff position of a detached bow shock from an obstacle is also reviewed. In addition, a detailed examination of the hydrodynamic equations along the boundary of the obstacle is performed. Lastly, the MHD relations along the obstacle surface are examined, for specific orientations of the upstream interplanetary magnetic field (IMF) in relation to the upstream flow velocity vector.     

Mass-loading and the formation of the Venus tail

Despite its lack of an intrinsic magnetic field Venus has a well defined magnetotail, containing about 3 megawebers of magnetic flux in a tail about 4 R_V across with perhaps a slightly elliptical cross section. This tail arises through the mass-loading of magnetic flux tubes passing by the planet. Mass-loading can occur due to charge exchange and photo-ionization as well as from the diffusion of magnetic field into the ionosphere. Various evidence exists for the mass-loading process, including the direct observation of the picked up ions with both the Venera and Pioneer Venus plasma analyzers.     

Fluctuating magnetic fields in the magnetosphere

The study of ULF waves in space has been in progress for about 12 years. However, because of numerous observational difficulties the properties of the waves in this frequency band (10^-3 to 1 Hz) are poorly known. These difficulties include the nature of satellite orbits, telemetry limitations on magnetometer frequency response and compromises between dynamic range and resolution. Despite the paucity of information, there is increasing recognition of the importance of these measurements in magnetospheric processes. A number of recent theoretical papers point out the roles such waves play in the dynamic behavior of radiation belt particles.At the present time the existing satellite observations of ULF waves suggest that the level of geomagnetic activity controls the types of waves which occur within the magnetosphere. Consequently, we consider separately quiet times, times of magnetospheric substorms and times of magnetic storms. Within each of these categories there are distinctly different wave modes distinguished by their polarization: either transverse or parallel to the ambient field. In addition, these wave phenomena occur in distinct frequency bands. In terms of the standard nomenclature of ground micropulsation studies ULF wave types observed in the magnetosphere include quiet time transverse — Pc 1, Pc 3, Pc 4, Pc 5 quiet time compressional — Pc 1 and Pi 1; substorm compressional Pi 1 and Pi 2; storm transverse — Pc 1; storm compressional Pc 4, 5. The satellite observations are not yet sufficient to determine whether the various bands identified in the ground data are equally appropriate in space.Publication No. 982. Institute of Geophysics and Planetary Physics, University of California, Los Angeles, Calif. 90024.