Surface materials of the Viking landing sites

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

The Environs of Viking 2 Lander

Forty-six days after Viking 1 landed, Viking 2 landed in Utopia Planitia, about 6500 kilometers away from the landing site of Viking 1. Images show that in the immediate vicinity of the Viking 2 landing site the surface is covered with rocks, some of which are partially buried, and fine-grained materials. The surface sampler, the lander cameras, engineering sensors, and some data from the other lander experiments were used to investigate the properties of the surface. Lander 2 has a more homogeneous surface, more coarse-grained material, an extensive crust, small rocks or clods which seem to be difficult to collect, and more extensive erosion by the retro-engine exhaust gases than lander 1. A report on the physical properties of the martian surface based on data obtained through sol 58 on Viking 2 and a brief description of activities on Viking 1 after sol 36 are given

Physical Properties of the Martian Surface from the Viking 1 Lander: Preliminary Results

The purpose of the physical properties experiment is to determine the characteristics of the martian "soil" based on the use of the Viking lander imaging system, the surface sampler, and engineering sensors. Viking 1 lander made physical contact with the surface of Mars at 11:53:07.1 hours on 20 July 1976 G.M.T. Twenty-five seconds later a high-resolution image sequence of the area around a footpad was started which contained the first information about surface conditions on Mars. The next image is a survey of the martian landscape in front of the lander, including a view of the top support of two of the landing legs. Each leg has a stroke gauge which extends from the top of the leg support an amount equal to the crushing experienced by the shock absorbers during touchdown. Subsequent images provided views of all three stroke gauges which, together with the knowledge of the impact velocity, allow determination of "soil" properties. In the images there is evidence of surface erosion from the engines. Several laboratory tests were carried out prior to the mission with a descent engine to determine what surface alterations might occur during a Mars landing. On sol 2 the shroud, which protected the surface sampler collector head from biological contamination, was ejected onto the surface. Later a cylindrical pin which dropped from the boom housing of the surface sampler during the modified unlatching sequence produced a crater (the second Mars penetrometer experiment). These two experiments provided further insight into the physical properties of the martian surface

The "Soil" of Mars (Viking 1)

The location of the Viking 1 lander is most ideal for the study of soil properties because it has one footpad in soft material and one on hard material. As each soil sample was acquired, information on soil properties was obtained. Although analysis is still under way, early results on bulk density, particle size, angle of internal friction, cohesion, adhesion, and penetration resistance of the soil of Mars are presented