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Published online by Cambridge University Press: 25 May 2016
I review the dynamical measurements of mass in the solar neighborhood and show that, within 1 kpc, ∼ 40% is unaccounted for by known stars and gas. I discuss several interpretations of the data including the ‘standard model’ where the extra mass is due to a spherical dark halo. I argue that the evidence for a radically different picture of an ultra-flat distribution is at least as compelling as the standard model.