mode.

As is described by Jewitt (1997) and Frouard & Efroimsky (2018), in the presence of any damping for kinetic energy, a cometary nucleus in an excited state (i.e., one that is above lowest energy) will always tend to reach a lowest-energy state.

The two comets 1P and 103P are regarded as undergoing nonprincipal axis rotation, with the possibility that other comets may also exhibit this behavior, as is proposed by Knight et al. (2024).

Conversely, the majority of comets do not exhibit indications of strongly excited rotation states.

In the case of comet 67P/C-G, Gutiérrez et al. (2016), Godard et al. (2017), and Kramer et al. (2019) report only a minor excitation from the lowest-energy state.

This and the fact that most comets do not show excited rotations (Knight et al. 2024) leads us to the assumption that the lowest-energy state reflects the properties of most known comets in an appropriate manner.

In this case, observational data for angular velocity can be used to assess torque directions.

Momentum is created by sublimation processes close to the surface of the cometary nucleus.

Incoming solar irradiation heats up the upper surface layers and is mostly reradiated into space.

The sublimation process consumes some fraction of the incoming energy, while the remaining energy propagates into subsurface layers, where other frozen volatiles might be present.

Thermophysical models (TPMs) describe these processes at a point on the surface of the nucleus, as is discussed by Keller et al. (2015a) and Blum (2018).

Complex TPMs consider the composition of the material on the surface and within the column of the subsurface domain, the temporal evolution of solar irradiation, and the energy fluxes within the column.

The analyses of the Rosetta images of comet 67P/C-G by Kramer & Noack (2016), Gundlach et al. (2020), and Fulle et al. (2020) point to very low values of heat conductance, and thus sublimation of water occurs almost instantaneously with respect to the incoming radiation.

Due to a higher sublimation rate at lower temperatures, CO2 emission can occur even at night.

Here, we constrict the discussion to TPMs that establish sublimation flux as an instantaneous response to the incoming irradiation.

These models balance reradiation due to scattering or thermal activity and sublimation energy.

Heat transfer into the cometary material is neglected.

An increase in sublimation is related to an increase in irradiation (monotonous function).

In this case, no heat flow to the subsurface layers or any other delaying process is considered.

An example of such an approach is model A in Keller et al. (2015b), which is based on the energy balance for incoming radiation and outgoing thermal and sublimation fluxes on the surface.

The shape of the nucleus is of particular importance for rotational dynamics.

In addition to the tensor of inertia, the Article number, page 2
formation of torques is strongly affected by the local geometry of the surface faces with respect to the rotational axis.

The basic geometry-driven effects can already be studied for simplified ellipsoidal shapes.

More complex body shapes further complicate the analysis, for instance, by introducing concavities.

Concavities change the irradiation by self-shadowing and lead to significant variability in the regional torque directions.

The basic effect of concavities can be studied for a shape with a simplified bilobed structure.

Shapes that approximate the nucleus of comet 67P/C-G bring along further complexity, including surface roughness and boulders, which are not resolved in the typical grid sizes used for torque computations.

We study the dependence of the torque on the mesh size using remeshed versions of the shape model of Preusker et al. (2017) for comet 67P/C-G.

Also for other comets shape models have been derived.

The combination of light curve inversion for convex bodies of Kaasalainen (2001) and radar imaging of Ostro et al. (2002) yield coarse resolution for surface geometry such as in Donaldson et al. (2023) for 162P/Siding Spring and in Magri et al. (2011) for Asteroid (8567) 1996 HW1.

From spacecraft imagery the shapes of comets 1P, 9P, 19P, 67P, 81P, and 103P are constrained (see Snodgrass et al. 2022).

Knight et al. (2024) classify four of these comets as having a bilobed shape.

Observational data for the rotation state of comets are mainly extracted from light curves and radar detections.