Seasonal CO ₂ Cycle at the Martian Poles Revealed by Sounding Radar

Abstract Seasonal CO 2 frost accumulates and ablates at the Martian poles during night and day, respectively. We report the first robust measurements of polar seasonal change in SHAllow RADar (SHARAD) data, based on calibration of the 16‐year data set. At each pole, radar surface echo power varies annually by ∼3–4 dB (increase of 2–2.5 times in power) with a distinct temporal signal, where power decreases during the night and increases during daytime, although spatial heterogeneities exist. Power variations are restricted to the surface reflection. The timing and magnitude of radar power variations are largely consistent with the deposition and removal of CO 2 frost, despite predicted seasonal frost layers being thinner than a SHARAD range cell. Radar power variations largely agree with previous analyses. This study represents the first documentation of the full seasonal CO 2 frost cycle at both Martian poles using radar sounder data.