The image of Hydra recently released shows a sharply edged black half oval cutting deep into its bottom as in the image below. Is it dark sky behind an open gap we see, or just unreflective matter on that surface patch? If the latter, could it be similar with the upper right black part of it too, that gives it its apparent shape of an axes head? I've not read or heard any comments about this yet. Is it likely to be figured out from New Horizon data?
(B) LORRI panchromatic (350 to 850 nm) image of Hydra at 1.13 km/pixel, solar phase angle 34°
roughly 43 km × 33 km
The feature then I suppose is about 6-9 km wide and high, as seen. But with pixels at 1 km its regularity can maybe not be trusted. Hydra is about 10 times as large as comet 69/P, and looks almost more incredibly irregularly shaped.