Overview
- High‑resolution SHARAD passes detected only very weak, diffuse reflections at the base of the south polar ice, inconsistent with a conductive water layer.
- The signals are roughly a thousand times weaker than the bright 2018 returns seen by ESA’s lower‑frequency MARSIS instrument.
- Engineers rolled Mars Reconnaissance Orbiter by 120 degrees on May 26, 2025 to enable the polar-facing measurements.
- Modeling reported in Geophysical Research Letters found dust attenuation or similar effects cannot explain the weak SHARAD echoes.
- Researchers now favor non‑aqueous explanations such as smectite clays or a smoother subsurface unit like an impact‑filled or volcanic layer, while noting the debate is not closed.