Surface materials of the Viking landing sites

摘要: Martian surface materials viewed by the two Viking landers (VL-1 and VL-2) range from fine-grained nearly cohesionless soils to rocks. Footpad 2 of VL-1, which landed at 2.30 m/s, penetrated 16.5 cm into very fine grained dunelike drift material; footpad 3 rests on a rocky soil it ≈3.6 cm. Further penetration may have been arrested hard substrate. Penetration is less than would be expected for typical lunar regolith. During landing, retroengine exhausts eroded propelled grains rocks produced craters impact with surface. Trenches excavated in material sampler steep walls up 6 relief. Incipient failure failures end trenches are compatible cohesion near 10–10^2 N/m^2. Trenching clods possibly In five samples, commanded extensions were not achieved, situation indicating that buried or local areas large cohesions (≥10 kN/m^2) both present. VL-2, velocity between 1.95 2.34 partly rock, appears struck one; leg strokes small. Retroengine more erosion occurred VL-1 owing increased thrust levels just before touchdown. Deformations doming without visible fracturing accompanied production angular clods. Although larger 3.0 abundant repeated attempts collect 0.2–1.2 across imbedded indicate this size scarce. There no evidence while was pushing nudging ≈25 across, spalled, chipped, fractured Preliminary analyses motor currents (≈25 N force resolution) during normal sampling consistent frictional (ϕ ≈ 36°) weakly cohesive frictionless (C < kN/m^2). The Mars has friction.