A Single Deformed Bow Shock for Titan‐Saturn System

Abstract

During periods of high solar wind pressure, Saturn's bow shock is pushed inside Titan's orbit exposing the moon and its ionosphere to the solar wind. The Cassini spacecraft's T96 encounter with Titan occurred during such a period and showed evidence for shocks associated with Saturn and Titan. It also revealed the presence of two foreshocks: one prior to the closest approach (foreshock 1) and one after (foreshock 2). Using electromagnetic hybrid (kinetic ions and fluid electrons) simulations and Cassini observations, we show that the origin of foreshock 1 is tied to the formation of a single deformed bow shock for the Titan‐Saturn system. We also report the observations of a structure in foreshock 1 with properties consistent with those of spontaneous hot flow anomalies formed in the simulations and previously observed at Earth, Venus, and Mars. The results of hybrid simulations also show the generation of oblique fast magnetosonic waves upstream of the outbound Titan bow shock in agreement with the observations of large‐amplitude magnetosonic pulsations in foreshock 2. We also discuss the implications of a single deformed bow shock for new particle acceleration mechanisms and also Saturn's magnetopause and magnetosphere.

Formation and Topology of Foreshock Bubbles

“…The resulting time series data show the classic features of an FB with the spacecraft first encountering the core region, followed by the sheath plasma and the shock wave. An interesting aspect of planar FBs is that their shock and the bow shock combine into a single deformed bow shock similar to what happens at the Titan-Saturn system during periods of high solar wind pressure (Omidi et al, 2017). Under these conditions, ions escaping the quasi-parallel bow shock can interact with the quasiperpendicular portions of the bow shock resulting in further acceleration through shock drift processes.…”

Dayside Transient Phenomena and Their Impact on the Magnetosphere and Ionosphere

“…Based on the radial nature of the IMF and symmetry around it, the FCB is a cylindrical boundary in 3-D (see 3-D example in Omidi et al. 2017b ).

Fig.

…”

“…For example, Omidi et al. ( 2017b ) performed hybrid simulations of the solar wind-Venus interaction and theoretically predicted the occurrence of foreshock cavitons and foreshock compressional boundaries.…”

Motion of Classic and Spontaneous Hot Flow Anomalies Observed by Cluster

“…The foreshock is the region where the magnetic field lines are connected to the bow shock and filled with particles reflected from the bow shock (Eastwood et al., 2005). Many foreshock transient phenomena such as hot flow anomalies (HFAs; Schwartz, 1995; Schwartz et al., 1985), spontaneous hot flow anomalies (SHFAs; Omidi et al., 2013, 2015; Zhang et al., 2013), foreshock bubbles (Omidi et al., 2010; Wang, Wang et al., 2020; Wang et al., 2021), cavitons (Blanco‐Cano et al., 2009; Omidi, 2007), cavities (Sibeck et al., 2002, 2004, 2008), and density holes (Parks et al., 2006) have been widely observed near the Earth's bow shock (Bai et al., 2020; Chu et al., 2017; Liu et al., 2020; Thomsen et al., 1986; Turner et al., 2020; Zhang et al., 2010) and other planetary bow shocks (Collinson et al., 2012, 2014, 2017; Masters et al., 2008; Oieroset et al., 2001; Omidi et al., 2017, 2020; Slavin et al., 2009; Uritsky et al., 2014; Valek et al., 2017). These kinetic processes in the foreshock can affect the magnetosheath, magnetosphere, and ionosphere (Gutynska et al., 2015; Sibeck et al., 2003).…”