Abstract: Type Ia supernovae have famously been used as standard candles, a use that led to the discovery that the expansion of the Universe was accelerating under the influence of a mysterious new phenomenon called “dark energy.” And yet, we still do not have a clear picture of what types of star systems (the “progenitors”) end up exploding as these supernovae. Most astronomers observe Type Ia supernovae when they are young and at their brightest. In my talk, I will present recent results from Hubble Space Telescope observations of nearby Type Ia supernovae taken hundreds of days after explosion, when the supernovae are a million times fainter than at peak. These studies reveal a possible new correlation between the intrinsic luminosity of the supernovae and the way their luminosity fades at these late times. If confirmed, this correlation could provide a brand new diagnostic of Type Ia supernova progenitor, explosion, and nebular physics.