High Ice Purity of Martian Lobate Debris Aprons at the Regional Scale: Evidence From an Orbital Radar Sounding Survey in Deuteronilus and Protonilus Mensae

Lobate Debris Aprons (LDA) are martian landforms with a strong morphologic resemblance to rock glaciers and debris‐covered glaciers. While the Shallow Radar (SHARAD) sounder has confirmed that a handful of LDA are composed of >80% water ice, viscous flow morphology can also be produced by as little as 30% ice. To distinguish between these endmembers, we conducted a comprehensive regional SHARAD survey of LDA, in Deuteronilus Mensae. We found that the majority of LDA are penetrated by SHARAD and determined that they are composed of a material with ε ′ = 3 and t a n δ ≈0.002 < 0.005. These LDA are thus consistently composed of >80% water ice, which constrains the regional sequestered ice budget to a minimum of 0.9 − 1.0 × 10 5  km 3 or a 62–69‐cm Global Equivalent Layer.