The Ursa Minor dwarf spheroidal shows a pronounced secondary density peak and other clumpy stellar substructures that appear kinematically cold and long-lived, implying they have survived for many crossing times inside a galaxy that is otherwise highly dark-matter dominated (Kleyna et al. 2003; Pace et al. 2014). In ΛCDM, such cold clumps should be rapidly sheared out or heated and dissolved if Ursa Minor sits in a cuspy, subhalo-rich dark-matter potential, so their persistence instead points toward a large, nearly harmonic central core and a smoother halo than standard simulations predict, adding to the small-scale core–cusp and substructure tensions (Lora et al. 2012; Bullock & Boylan-Kolchin 2017).