Abstract Electromagnetic instabilities in the collisional lower Martian ionosphere are investigated using a two‐fluid model that incorporates collisional effects and density gradients. The model accounts for magnetization asymmetry between electrons and ions, where electrons remain magnetized while ions are strongly coupled to neutrals. A general dispersion relation is derived, capturing both real frequency and growth rate of unstable modes. Limiting‐case analysis of the dispersion relation highlights the essential role of cross‐field electron drift, collisional resistive coupling, and background density gradients as sources of free energy. The analysis identifies a hybrid electromagnetic instability that develops over intermediate perpendicular wavelengths, driven by gradient‐drift processes but modulated by magnetic‐pressure and collisional dissipation. Numerical solutions reveal distinct parametric regimes controlled by ion‐neutral and electron‐neutral collisionalities, magnetic‐pressure, and density gradient strength. Growth rates exhibit well‐defined unstable windows in both wavenumber and parameter space, with optimal instability occurring at moderate ion collisionality and low‐to‐moderate electron collisionality. The model explains the key physical mechanisms responsible for small‐scale plasma irregularities observed by MAVEN at altitudes below 200 km, providing a theoretical framework for interpreting electromagnetic fluctuations in the weakly ionized Martian ionosphere.
Al‐Buradah et al. (2026) studied this question.