A verified physical model for the stratification of planetary regolith

We introduce a ready-to-use regolith stratification model for airless Solar System bodies, built on laboratory and literature data describing granular-media compression. Under the influence of gravity, regolith becomes progressively denser with increasing depth (Schräpler et al. 2015, Bürger et al. 2024) . We quantify this densification by extracting key parameters from experimentally determined compression curves (Blum et al. 2026).

To establish the model, we analysed compression data for various granular SiO₂ samples and determined the turnover pressure, i.e. the stress p_m at which the material transitions from a loose to a compact state, and the logarithmic width of this transition Δ. We then correlated the packing fraction with grain size r to link particle radius to the turnover pressure. Our analysis covers grain radii from approximately r=0.5 µm to r=100 µm and reveals a power-law relationship p_m~r^-2, in agreement with a theoretical dust-aggregate compression model (Tatsuuma et al. 2023).

The regolith-stratification model was indirectly validated by providing a unique solution for grain size, transition width and deep-layer density for the lunar regolith when thermal radiation from LRO/Diviner and Chang'E-2/MRM over a wide wavelength range are taken into account and compared to a thermophysical model (Bürger et al. 2026).

Finally, we present the full stratification model along with all relevant free parameters determined from the data. Valid across a wide range of grain sizes and materials, this model provides a practical tool for estimating density profiles in the regolith of moons, asteroids, and comets. 

References:

J. Blum, J. Cybulski, G. Meier, B. Gundlach, C. Güttler, J. Bürger 2026. The stratification of planetary regolith: investigating the relation between turnover pressure and grain size, Astronomy & Astrophysics 707, A361.

J. Bürger, J. Feng, M.A. Siegler, J. Blum 2026. A microphysical thermal model for the lunar regolith: determining the lunar regolith properties using a combination of LRO/Diviner and Chang’E-2/MRM data, Astronomy & Astrophysics, accepted.

J. Bürger, P. Hayne, B. Gundlach, M. Läuter, T. Kramer, J. Blum 2024. A microphysical thermal Model for the lunar regolith: investigating the latitudinal dependence of regolith properties, JGR Planets 129, e2023JE008152.

R. Schräpler, J. Blum, I. von Borstel, C. Güttler 2015. The stratification of regolith on celestial objects, Icarus 257, 33-46.

M. Tatsuuma, A. Kataoka, S. Okuzumi, H. Tanaka 2023. Formulating compressive strength of dust aggregates from low to high volume filling factors with numerical simulations, The Astrophysical Journal 953, id.6.