Meter-scale thermal contraction crack polygons on the nucleus of comet 67P/Churyumov-Gerasimenko
2018
We report on the detection and characterization of more than 6300
polygonson the surface of the nucleus of comet 67P/Churyumov-Gerasimenko, using images acquired by the
OSIRIScamera onboard Rosetta between August 2014 and March 2015. They are found in consolidated terrains and grouped in localized networks. They are present at all latitudes (from North to South) and longitudes (head, neck, and body), sometimes on pit walls or following
lineaments. About 1.5% of the observed surface is covered by
polygons.
Polygonshave an homogeneous size across the nucleus, with 90% of them in the size range 1 – 5 m and a mean size of 3.0 ± 1.4 m. They show different morphologies, depending on the width and depth of their trough. They are found in networks with 3- or 4-crack intersection nodes. The
polygonsobserved on 67P are consistent with thermal contraction crack
polygonsformed by the diurnal or seasonal temperature variations in a hard (MPa) and consolidated sintered layer of water ice, located a few centimeters below the surface. Our thermal analysis shows an evolution of thermal contraction crack
polygonsaccording to the local thermal environment, with more evolved
polygons(i.e. deeper and larger troughs) where the temperature and the diurnal and seasonal temperature range are the highest. Thermal contraction crack
polygonsare young surface morphologies that probably formed after the injection of 67P in the inner solar system, typically 100 000 years ago, and could be as young as a few
orbital periods, following the decreasing of its perihelion distance in 1959 from 2.7 to 1.3 a.u. Meter scale thermal contraction crack
polygonsshould be common features on the nucleus of Jupiter family comets.
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