[X] My Assistant

[David]

I'm looking at two animations of the asteroid 4 Vesta: the first is a sequence of images from the HST; the second several seconds of one HST image followed by a partial rotation of a shape model.

Why do I get the impression that these two animations are depicting different objects? I admit that much less of the rotation is shown in the shape model animation, which may lie behind the differences in impression, but that itself seems to me to be a problem. The shape model looks like a smooth oblate spheroid, with some distortion at the bottom (south?) pole, whose shape doesn't vary very much as it rotates. The HST sequence shows some pretty drastic changes in Vesta's profile as it rotates, including what must be a huge off-center crater in the upper (northern?) hemisphere, while the shape of the lower hemisphere is not nearly as flat as the shape model suggests. And yet one meets with quite a lot of references to Vesta being a "spheroid", which is hardly the impression I get from the HST rotation sequence. What gives?