Investigating grain size in the Martian mantle: Implications of basal mantle layers and viscoelastic models

This study examines the grain size in the Martian mantle using viscoelastic dissipation models and two interior structural configurations: S23M1 (without a basal mantle layer, BML) and S23M2 (with a BML). Results indicate substantial variations in grain size estimates depending on the viscoelastic model employed. For instance, Andrade(μ-β) models suggest smaller grain sizes (∼1 mm), while Burgers(background), Burgers(+peak), and Andrade(fixed β) models predict a broader range of 0.1–10 cm. Sundberg-Cooper models, by contrast, yield larger grain sizes (>0.5 cm). The inclusion of a BML generally leads to smaller grain size estimates. For instance, Sundberg-Cooper predictions decrease from ∼10 cm to ∼0.8 cm with a BML, attributed to altered average rigidity of Mars that reduces elastic response. These findings stress the importance of mantle structure in interpreting viscoelastic properties and reconciling laboratory-derived constraints with geophysical observations. Future tidal measurements are critical for refining these models further.