Topics and/or questions for future investigations include the following:
The least luminous galaxies are often disproportionately interesting. What sorts of bound stellar/gaseous objects will the next generation of sky surveys detect?
This field will continue to develop in proportion to 1) the rate at which data sets grow in size and quality and 2) the efficiency with which analytical tools can extract the information contained therein. Promising strategies for analysis include the formulation of statistical likelihood functions that depend on discrete measurements (e.g., of individual stellar positions and velocities) rather than on binned profiles, and exploitation of multi-component structure/substructure that is present in the data.
All dSphs clearly deviate from the simple models invoked to characterise their observed properties. In order to understand dSphs as galaxies, one must consider not only the structural and kinematic data emphasised above, but also chemical abundances, star formation histories (i.e., stellar masses), internal substructure and external environment.
The outer stellar structures of dSphs carry valuable information about the gravitational competition between the Milky Way and its satellites. Combined with deep photometric surveys that map the Galactic stellar halo, wide-field spectroscopic surveys that reach large galactocentric distances in dSphs will reveal details of the transition from satellite to host potential.
The standard CDM hypothesis seems to require baryon-physical processes to have formed large constant-density cores in galactic dark matter halos. Do the internal mass distributions of galaxies correlate with other observables directly related to baryon physics (e.g., luminosity, metallicity, star formation history)? Constraints on core sizes for the least luminous dSphs would be extremely valuable.
Can observations and/or experiments provide clear evidence for non-gravitational interactions involving a dark matter particle? Can observations provide evidence for gravitational interactions involving dark matter halos on subgalactic scales?
Are there cosmological and/or particle physics models for dark matter from which can be extracted accurate predictions regarding the stellar dynamics of the most dark-matter dominated galaxies?
The author is grateful to Gerry Gilmore for the invitation to write this review and for insightful comments. The author thanks Giuseppina Battaglia, Alexey Boyarsky, Alexander Kusenko, Oleg Ruchayskiy and Ed Olszewski for suggestions that improved the quality of this work. MGW is supported by NASA through Hubble Fellowship grant HST-HF-51283.01-A, awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.