Double layers and solitary waves in Martian upper ionosphere

Abstract Recent observations from NASA’s Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft at an altitude of 350–600 km are consistent with intense plasma wave activity. A unipolar feature (i.e., identified as a double layer) was observed, which is followed by a bipolar structure (i.e., solitary pulses). These nonlinear waves are presumably produced in the ion-acoustic frequency range, which is in conjunction with accelerated ions. The Martian upper ionosphere is identified by the presence of hydrogen ( H + ), oxygen ( O + ), and oxygen molecule ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:msubsup> <mml:mrow> <mml:mi>O</mml:mi> </mml:mrow> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> </mml:mrow> </mml:msubsup> </mml:math> ) ions, including background superthermal electrons. With the aid of a hydrodynamic description, the plasma model in this environment was analyzed through deriving an energy-balance-like equation. The existence domains, electric field, pulse time duration, and frequency range of both the double layer and solitary structure are determined. We examined how plasma parameters affect these pulses’ fundamental characteristics. It is found that supersonic compressive ion-acoustic solitary and double layer pulses can exist. Solitary waves are expected to exhibit an electric field of approximately 30 mV/m, with spatial width around 10 λ Di , a time duration of less than 8 ms, and a fast Fourier transform of one solitary structure with a frequency range of ∼ 0.6–1.4 kHz. On the other hand, the double layers have an electric field in the range ∼ 60–100 mV/m across spatial and temporal widths of ∼ 10 λ Di and ∼ 8 ms, and a fast Fourier transform of one double layer structure has a frequency range of ∼ 1.1–1.3 kHz. In addition, it has been observed that the steepness of solitary and double layer structures increases when the values of H + ion number density and superthermality parameter are increased or when the value of O + ion number density is decreased.