Do comet fractures drive surface evolution?

Extreme thermal stresses experienced by a comet as it orbits around the Sun could explain the extensive fracturing thought to drive its long-term surface erosion, say Rosetta scientists analysing high-resolution images of Comet 67P/Churyumov-Gerasimenko’s surface. The study, which is published online in the journal Geophysical Research Letters, is based on images taken between 6 August 2014 – when Rosetta first arrived at the comet – and 1 March 2015, and includes detailed images acquired from between just 8 and 18 km from the comet’s surface. Ramy’s team identified three distinct settings in which the fractures occur: networks of long narrow fractures, fractures on cliffs and fractured boulders. In addition, several unique features were identified: the parallel fractures running across Hathor’s 900 m-high cliffs, an isolated 500 metre-long crevice in the Anuket region of the comet’s neck, and a 200 m-long complex crack system in Aker on the large lobe. “The fractures show a variety of morphologies and occur all over the surface and at all scales: they are found in the towering 900 m-high cliffs of Hathor right down to the surfaces of boulders a few metres across,” describes lead author M. Ramy El-Maarry from the University of Bern. The most prevalent setting appears to be networks of narrow fractures that extend for a few metres to 250 m in length, typically on relatively flat surfaces. Interestingly, in some locations, the fractures appear to cross cut each other in polygonal patterns at angles of 90º – on Earth and Mars this is often an indicator of ice that has contracted below the surface. Another family of cross-cutting fractures is observed on cliff faces, such as in the Seth region on the comet’s large lobe, with debris deposits littering their bases. Fractured cliff faces were also observed at Abydos, the final […]

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