Research Groups

Planetary Imaging Group (PIG)

Rosetta/OSIRIS at comet Churyumov-Gerasimenko

The morphological diversity of comet 67P/Churyumov-Gerasimenko

During the two years mission of Rosetta the camera OSIRIS onboard the spacecraft Rosetta has extensively acquired images of the surface of the nucleus of 67P/Churyumov-Gerasimenko at high resolution (up to tens of centimeters by pixel). These detailed observations revealed the complex bi-lobate shape of the nucleus and the morphological diversity of its surface (Fig. 1). Indeed we discovered the presence of amazing features (Fig. 2) which include for instance cliffs, overhangs, large depressions, layers, fractures, polygons, boulders, pinnacles, small pits or smooth-looking terrains where features that resemble to dunes on Earth formed! Therefore comets appear to be complex geologic worlds with features that are the expression of different physical processes.

[LEFT] Figure 1: OSIRIS (NAC) image of 67P/Churyumov-Gerasimenko acquired on the 06/08/2014 showing the morphological diversity of the nucleus. [RIGHT] Figure 2: Examples of morphological features observed at the surface of 67P/Churyumov-Gerasimenko. Up, left: clusters of bright spots likely to be H2O ice rich observed in Khepry (Pommerol et al. 2015). Up, right: “Aeolian-like” ripples (indicate by red arrow) observed in the Hapi region (Thomas et al. 2015). Down, left: fractures (indicate by yellow arrows) in the neck region (El-Maary et al. 2018). Down, right: large boulder (indicate by yellow arrow) that has been observed to move in the Khonsu region (El-Maary et al. 2018).

From all the information collected we defined and mapped regions and sub-regions at the surface of 67P’s nucleus based on the morphological characteristics of the different areas (Fig. 3).

boundaries
Figure 3: Regional definitions based on large-scale unit boundaries (Thomas et al., 2015)

We observed the presence of different terrain textures with consolidated terrains which looks likes rocks on Earth and unconsolidated terrains composed of dust deposits and pebbles/boulders. Although we know comets are partially composed of H2O ice from the analysis of the outgassing gases, the observation of ice at the surface is limited. Analyses of the different spectral filters of the OSIRIS imaging system permitted to identify the presence of localized patches of H2O ices at the surface of the comet. The constant monitoring during the two years mission allowed the observation of surface changes such as fracture extensions, boulders movement (up to tens meters wide), cliffs collapse or dust redistribution. The presence, at some locations of the unconsolidated and smooth terrains, of “aeolian-like” features that looks like to features observed on planetary surfaces such the Earth, Mars or the icy moon Titan, was an unexpected surprise as the comet display no atmosphere. These features show evolution during periods before and after perihelion, therefore it's an ongoing process but the physics that drive their formation is still uncertain.

This work have been supported and enhanced by the MiARD project.

 

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Publications

El-Maarry, M.R., Thomas, N., Giacomini, L., et al. (2015). Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images. Astronomy and Astrophysics, 583, A26.
 
El-Maarry, M.R., Thomas, N., Gracia-Berná, A., et al. (2015). Fractures on comet 67P/Churyumov-Gerasimenko observed by Rosetta/OSIRIS. Geophysical Research Letters, 42(13), 5170-5178.
 
El-Maarry, M.R., Thomas, N., Gracia-Berná, A., et al. (2016). Regional surface morphology of comet 67P/Churyumov-Gerasimenko from Rosetta/OSIRIS images: The southern hemisphere. Astronomy and Astrophysics, 593, A110.
 
El-Maarry, M.R., Groussin, O., Thomas, N., et al. (2018). Surface changes on comet 67P/Churyumov-Gerasimenko suggest a more active past. Science.
 
Giacomini, L., Massironi, M., El-Maarry, M.R., et al. (2016). Geologic mapping of the Comet 67P/Churyumov–Gerasimenko's Northern hemisphere. MNRAS, 462, S352-S367.
 
Pommerol, A., Thomas, N., El-Maary, M.R., et al. (2015). OSIRIS observations of meter-sized exposures of H2O ice at the surface of 67P/Churyumov-Gerasimenko and interpretation using laboratory experiments. Astronomy and Astrophysics, 583, A25.
 
Sunshine, J., Thomas, N., El-Maarry, M.R. (2016). Evidence for geologic processes on comets. Journal of Geophysical Research: Planets, 121(11), 2194-2210.
 
Thomas, N., Keller, H.U., Arijs, E., et al. (1998). Osiris - The optical, spectroscopic and infrared remote imaging system for the Rosetta orbiter. Advances in Space Research, 21(11), 1505-1515.
 
Thomas, N., Sierks, H., Barbieri, C., et al. (2015). The morphological diversity of comet 67P/Churyumov-Gerasimenko. Science 347 (6220), 1–6.
 
Thomas, N., Davidsson, B., El-Maarry, M.R. et al., (2015). Redistribution of particles across the nucleus of comet 67P/Churyumov-Gerasimenko. Astronomy and Astrophysics, 583, A17.