No abstract

No abstract

We present a statistical analysis of the distribution of large scale topographic features on comet 67P/Churyumov-Gerasimenko. We observe that the cumulative cliff height distribution across the surface follows a power law with a slope equal to −1.69 ± 0.02. When this distribution is studied independently for each region, we find a good correlation between the slope of the power law and the orbital erosion rate of the surface. For instance, the northern hemisphere topography is dominated by structures on the 100 m scale while the southern hemisphere topography, illuminated at perihelion, is dominated by 10 m scale terrain features. Our study suggest that the current size of a cliff is controlled not only by material cohesion but by the dominant erosional process in each region. This observation can be generalized to other comets, where we argue that primitive nuclei are characterized by the presence of large cliffs with a cumulative height power index equal to or above -1.5, while older, eroded cometary surfaces have a power index equal to or below -2.3. In effect, our model shows that a measure of the topography provides a quantitative assessment of a comet's erosional history, i.e. its evolutionary age.

Previous investigations of impact-induced atmospheric erosion considered mainly crater-forming impacts. Simple estimates show that in dense primary planetary atmospheres, considerable erosion could be induced by aerial bursts resulting from impacts of 1 to 10 km sized projectiles. Numerical simulations of cometary and asteroidal impacts (striking unmodified and crater-forming, impacting as fragmented meteorites, or causing aerial bursts) into dense (200 bar) atmospheres of different temperatures have been performed to obtain the amount of atmospheric erosion. The results have been approximated by simple analytical formulae.

Aims. We investigate the influence of the Yarkovsky force on the long-term orbital evolution of Jupiter Trojan asteroids. Methods. Clones of the observed population with different sizes and different thermal properties were numerically integrated for 1 Gyr with and without the Yarkovsky effect. The escape rate of these objects from the Trojan region as well as changes in the libration amplitude, eccentricity, and inclination were used as a metric of the strength of the Yarkovsky effect on the Trojan orbits. Results. Objects with radii R ≤1 km are significantly influenced by the Yarkovsky force. The effect causes a depletion of these objects over timescales of a few hundred million years. As a consequence, we expect the size-frequency distribution of small Trojans to show a shallower slope than that of the currently observable population (R 1 km), with a turning point between R = 100 m and R = 1 km. The effect of the Yarkovsky acceleration on the orbits of Trojans depends on the sense of rotation in a complex way. The libration amplitude of prograde rotators decreases with time while the eccentricity increases. Retrograde rotators experience the opposite effect, which results in retrograde rotators being ejected faster from the 1:1 resonance region. Furthermore, for objects affected by the Yarkovsky force, we find indications that the effect tends to smooth out the differences in the orbital distribution between the two clouds. Key words. Jupiter Trojan Asteroids -Yarkovsky effect -Numerical integration−6 J K -1 m -2 s -0.5 has been determined for (624) Hektor (Hanuš et al. 2015), while for (1173) Anchises, a higher value in the range Article number, page 1 of 10