Table 2 Reference model properties of the surface regolith of Phobos

Particle size

30 µm–10 cm

Model 1: very fine (< 300 µm)

Model 2 (nominal): 100 µm-5 mm

Model 3: > 1 mm

Particle size distribution

Power index 0.0–4.0

Power index ~ 3.0

Particle shape

Round to very angular

Subangular to angular

Internal friction angle of the particles

< 10 to > 55 degrees

30–50 degrees

Cohesion of particles

0–2000 N/m²

50-700 N/m²

Compressional strength of particles

0.5–70 MPa

Model a: 1–10 MPa

Model b: 30–50 MPa

Macroscopic porosity

< 10–70%

40–70%

Surface mobile particle-layer thickness

< 1 to > 100 m

5 m (can continue much deeper, but deeper parts are considered as mechanically stable)