  Cosmological distances inferred from supernova Ia observations constitute the
most direct and solid evidence for the recently detected accelerated expansion
of the universe. In this contribution, we show some inconsistencies between two
of the main light-curve fitters used for the elaboration of supernova Ia data
sets, opening new observational challenges regarding the use of these
luminosity distances when combined with CMB and BAO data. We also mention
ongoing analysis related to alternative models. The resolution of these
challenges will be crucial for XXI century cosmology.
