Solar wind flow about the outer planets: Gas dynamic modeling of the Jupiter and Saturn bow shocks

Abstract

Pioneer 10 and 11 and Voyager 1 and 2 observations are used to study global aspects of the solar wind interaction with Jupiter and Saturn. Solar wind measurements before and after the encounters are used to determine average upstream flow parameters at 5 and 9 AU. Bow shock and magnetopause position are found to vary as the fourth root of dynamic pressure at Jupiter and the sixth root at Saturn. The average distances to the nose of the magnetopause based upon the Pioneer and Voyager boundary crossings for Jupiter and Saturn are 68 RJ and 19 RS, respectively, after correction for varying solar wind pressure. In shape, the Jovian bow shock and magnetopause surfaces are similar to their terrestrial counterparts, but the width of the magnetosheath is 45% less than predicted by axisymmetric gas dynamic theory. This result is interpreted as evidence for strong polar flattening of the Jovian magnetosphere. The Saturnian magnetopause and bow shock boundaries are significantly more flared than at the earth with a subsolar magnetosheath that is 20% thinner than predicted by gas dynamic theory. On the basis of these results it is suggested that Saturn is intermediate between the earth and Jupiter in terms of polar flattening, with the unusual flaring of the Saturn magnetopause being due to the low ratio of static to dynamic pressure in the distant heliosphere.

The dusk flank of Jupiter's magnetosphere

“…The detectors on the Cassini mission are speci®cally designed to detect and`image' such energetic neutral atoms emanating from planetary magnetospheres. The magnetosphere imaging instrument (MIMI) 8 uses an ion and neutral camera (INCA) sensor that rejects charged particles and can detect energetic neutral atoms over the velocity range ,10 3 to ,10 4 km s -1 using a time-of-¯ight technique, with crude separation into light (that is, H, He) and heavy (that is, O, S) components. A second MIMI sensor, the charge±energy±mass spectrometer (CHEMS) is capable of determining independently the charge state, mass, and energy of ions over the range of ,3 to ,220 keV per charge.…”

Polar confinement of Saturn's magnetosphere revealed by in situ Cassini observations

“…The factor of 1.16 has been introduced to account for the 4% abundance of He 2+ in the solar wind which has a temperature approximately 4 times greater than the protons, as found by Slavin et al [1985]. Kanani et al [2010] explored the sensitivity of the model to the value of this factor, as well as the solar wind speed and the solar wind temperature but found that it was insensitive to varying these parameters within reasonable limits.…”

The Near-Saturn Magnetic Field Environment

“…In addition, the two boundaries may respond differently to the solar wind dynamic pressure [Slavin et al, 1985;Hendricks et al, 2005] hence a change in the dynamic pressure is not necessarily proportional to the magnetosheath subsolar and polar thicknesses i.e. the planetocentric distances between the magnetopause and the bow shock at X KSM = 0 and Z KSM = 0 respectively (neglecting aberration).…”

“…At 10 AU (1 AU = 1.5 × 10 8 km), typical values for k B T e and n e are ~1 eV [Slavin et al, 1985] and ~0.05 cm -3 [Crary et al, 2005] respectively yielding λ D ~ 30 m.…”

“…This is attributed to the decrease in the IMF strength since wave takes a size and shape similar to the obstacle [Billig, 1967]. Saturn's magnetosphere is a blunt body (as opposed to a pointed wedge) and a detached bow shock is thus formed in the dayside region [Slavin et al, 1985]. Cassini's orbits typically restrict bow shock crossings to the dayside region enabling detailed modelling of its three-dimensional size and shape [Masters et al, 2008;Went et al, 2011; the latter herein referred to as W11].…”