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Fig. 1
A family portrait of the comets imaged by recent space missions. a) comet 9P/Tempel 1; b) comet 81P/Wild 2; c) comet 103P/Hartley 2; and d) comet 67P Churyumov-Gerasimenko. Some circular depressions are discernable in these images. Image credits: a)–c)NASA; d) ESA/MPS.
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