Obviously without the image or knowledge of what Q16/Q17 are makes this tricky... but as a general rule, strings of craters are usually impact-related. They form when a loose body or collection of smaller objects (comets are commnly very loose) breaks up or spreads out as it approaches the surface, causing a trail of smaller impact craters, one for each piece, lying along the trajectory of the body.
See also comet Shoemaker-Levy 9: http://en.wikipedia.org/wiki/Comet_Shoemaker%E2%80%93Levy_9
Mar 21st, 2015
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