material just below the surface at the Abydos resting place of the Philae lander
(Spohn et al. 2015) might indicate that this process is important.
We can illustrate this further by using a two-layer model for the thermal conductivity in the 1-D heat transfer equation. An example result is shown in Fig. 2.35.
Here, we compare the temperature profile with depth of a case where there is a single
Fig. 2.34 The erosion of the surface caused by sublimation over one orbital period of the nucleus
of 67P using the model of Marboeuf et al. (2012). If the surface layer is porous, fractionation of the
ices occurs because highly volatile species can sublime at depth and the gas can escape. In this
example, CO is subliming around 4 m below the surface. Because of the high sublimation rate of
water ice near perihelion, the subliming CO 2 front is closest to the surface around perihelion (Credit:
C. Herny, pers. comm.)
Fig. 2.35 Temperature with depth for two models using the 1D heat equation. The dashed lines
show the dayside (heavy, dashed) and nightside (light, long dashed) temperature distribution for a
model with an increase in thermal conductivity of a factor of 20, 10 cm below the surface. The solid
and dot-dashed lines show the same model but with a constant low conductivity with depth. The
jump in thermal conductivity is intended to simulate a sub-surface ice layer. The internal temperature in both cases was set to 50 K
2.9 Surface Processes
99
(Spohn et al. 2015) might indicate that this process is important.
We can illustrate this further by using a two-layer model for the thermal conductivity in the 1-D heat transfer equation. An example result is shown in Fig. 2.35.
Here, we compare the temperature profile with depth of a case where there is a single
Fig. 2.34 The erosion of the surface caused by sublimation over one orbital period of the nucleus
of 67P using the model of Marboeuf et al. (2012). If the surface layer is porous, fractionation of the
ices occurs because highly volatile species can sublime at depth and the gas can escape. In this
example, CO is subliming around 4 m below the surface. Because of the high sublimation rate of
water ice near perihelion, the subliming CO 2 front is closest to the surface around perihelion (Credit:
C. Herny, pers. comm.)
Fig. 2.35 Temperature with depth for two models using the 1D heat equation. The dashed lines
show the dayside (heavy, dashed) and nightside (light, long dashed) temperature distribution for a
model with an increase in thermal conductivity of a factor of 20, 10 cm below the surface. The solid
and dot-dashed lines show the same model but with a constant low conductivity with depth. The
jump in thermal conductivity is intended to simulate a sub-surface ice layer. The internal temperature in both cases was set to 50 K
2.9 Surface Processes
99