Electrostatic waves and nonlinear structures in Titan’s ionosphere

Usman Saeed; Shaukat Ali Shan; Hamid Saleem

doi:10.1140/epjp/s13360-025-06204-4

EPJ

Electrostatic waves and nonlinear structures in Titan’s ionosphere

Usman Saeed¹^,2, Shaukat Ali Shan³^,4 and Hamid Saleem³^,5^a

¹ Theoretical Physics Department (TPD), National Centre for Physics (NCP), Shahdrah Valley Road, 44000, Islamabad, Islamabad Capital Territory, Pakistan
² Department of Space Science, Institute of Space Technology (IST), 1, Islamabad Expressway, 44000, Islamabad, Islamabad Capital Territory, Pakistan
³ Theoretical Research Institute, Pakistan Academy of Sciences (TRIPAS), Pakistan Academy of Sciences, 3 Constitution Ave, G-5/2, 44000, Islamabad, Islamabad Capital Territory, Pakistan
⁴ Theoretical Physics Division, PINSTECH, 45650, Islamabad, Islamabad Capital Territory, Pakistan
⁵ School of Natural Sciences (SNS), National University of Sciences and Technology (NUST), H-12, 44000, Islamabad, Islamabad Capital Territory, Pakistan

Received: 5 August 2024
Accepted: 9 March 2025
Published online: 16 April 2025

Abstract

The temporal and spatial scales associated with linear and nonlinear ion acoustic waves (IAWs) in Titan’s ionosphere have been estimated in the presence of an extremely small ambient magnetic field of the order of

B_{0} ≃ 2 \times 10^{- 4}

$B_0 \simeq 2 \times 10^{-4}$ G. Titan’s ionosphere has many kinds of positive and negative ions but for analytical calculations, the dominant ions HCNH⁺ and CN⁻ are taken into account along with free electrons keeping in view the observations of the Cassini spacecraft. The frequencies of IAW turn out to be of the order of (0.001) rad/s, and parallel wavelengths of the order of several kilometers, which are very different from Earth’s ionosphere. Shear flow-driven purely growing instability is also investigated. It is found that the IAWs become unstable in the presence of field-aligned shear flow of positive and negative ions. It is pointed out that the nonlinear IAWs can give rise to large solitary electrostatic structures with widths of the order of several hundred kilometers. The values of plasma beta corresponding to positive and negative ions are

β_{a} ≃ (0.046) ≪ 1

$\beta _{a}\simeq (0.046)\ll 1$ and

β_{b} ≃ (0.006) ≪ 1

$\beta _{b}\simeq (0.006)\ll 1$ , which are suitable for the propagation of electrostatic waves.

Usman Saeed, Shaukat Ali Shan and Hamid Saleem have contributed equally to this work.

12 Internat. Congress of the Balkan Physical Union
July 8-12, 2025
Bucharest, Romania

EPJ

Electrostatic waves and nonlinear structures in Titan’s ionosphere

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