Titan's near magnetotail from magnetic field and electron plasma observations and modeling: Cassini flybys TA, TB, and T3

Abstract

[1] The first close Titan encounters TA, TB, and T3 of the Cassini mission at almost the same Saturnian local time $1030 and in the same spatial region downstream of Titan have enabled us to study the formation of the tail of its induced magnetosphere. The study is based on magnetic field and electron plasma observations as well as threedimensional modeling. Our most important findings are the following: (1) No crossings of a bow shock of Titan were observed, and all encounters occurred at high plasma b > 1 for transsonic and trans-Alfvénic Mach numbers. (2) The magnetic draping signature of the induced magnetosphere often shows a sharp outer boundary called the draping boundary (DB) in the near-tail region. (3) The DB is often occurring as a discontinuity in magnetic field spatial derivatives, and therefore the DB is a discontinuity in the spatial distribution of plasma currents. (4) Perpendicular to the incident flow direction the DB shows an approximately elliptic cross section elongated along the incident magnetic field direction and a displacement toward the Sun. (5) We argue that the DB in the magnetic tail region corresponds to the boundary of a structure which is analogous to an Alfvén wing at very small b and in our case of larger b contains Alfvénic and slow mode features. It forms a tail like a delta wing in aerodynamics. (6) For the two less disturbed flybys, TA and T3, a polarity reversal layer has been observed with thicknesses of $320 km and $230 km, respectively.

On magnetospheric electron impact ionisation and dynamics in Titan's ram-side and polar ionosphere – a Cassini case study

“…Although chemistry dominates, the ionospheric structure can be modified by transport since the magnetic pressure at times is comparable to the thermal pressure down to the lowest observed altitude. This magnetospheric magnetic field is not efficiently shielded from the ionosphere, but rather diffuses slowly through and drapes around the ionosphere of Titan (Backes et al, 2005;Ness et al, 1982).…”

“…and dynamic (Backes et al, 2005;Neubauer et al, 2006). We have not at this stage taken into account the geometry effect of the magnetic field.…”

“…Usually the moon is inside Saturn's outer and nearly co-rotating magnetosphere. Regardless of the origin of the external magnetic field and plasma flow (magnetosheath or upstream solar wind) this interaction creates an induced magnetosphere around Titan (Ness et al, 1982;Backes et al, 2005) where various processes erode the ionosphere (Gurnett et al, 1982;Wahlund et al, 2005). The magnetospheric plasma flow of energetic particles also ionise the upper part of Titan's atmosphere.…”

Influence of Saturnian moons on Saturn kilometric radiation

“…The Alfvén wings of Titan as discussed by Neubauer et al [1984Neubauer et al [ , 2006 are much weaker than those of Io and may not support strong currents to the Kronian ionosphere. The influence of Titan on the magnetosphere of Saturn is not insignificant, however.…”

Interaction of Titan's ionosphere with Saturn's magnetosphere

“…We also note that the magnetic field orientation during this encounter was not nominal with an approximately 238 tilt (e.g. Backes et al 2005;Neubauer et al 2006). Therefore, the electric field direction will also be different from the nominal anti-Saturn direction.…”