Type Ia supernova science 2010-2020
  In the next decade Type Ia supernovae (SNe Ia) will be used to test theories
predicting changes in the Dark Energy equation of state with time. Ultimately
this requires a dedicated space mission like JDEM. SNe Ia are mature
cosmological probes --- their limitations are well characterized, and a path to
improvement is clear. Dominant systematic errors include photometric
calibration, selection effects, reddening, and population-dependent
differences. Building on past lessons, well-controlled new surveys are poised
to make strides in these areas: the Palomar Transient Factory, Skymapper, La
Silla QUEST, Pan-STARRS, the Dark Energy Survey, LSST, and JDEM. They will
obviate historical calibrations and selection biases, and allow comparisons via
large subsamples. Some systematics follow from our ignorance of SN Ia
progenitors, which there is hope of determining with SN Ia rate studies from
0<z<4.
  Aside from cosmology, SNe Ia regulate galactic and cluster chemical
evolution, inform stellar evolution, and are laboratories for extreme physics.
Essential probes of SNe Ia in these contexts include spectroscopy from the UV
to the IR, X-ray cluster and SN remnant observations, spectropolarimetry, and
advanced theoretical studies. While there are an abundance of discovery
facilities planned, there is a deficit of follow-up resources. Living in the
systematics era demands deep understanding rather than larger statistics. NOAO
ReSTAR initiative to build 2-4m telescopes would provide necessary follow-up
capability. Finally, to fully exploit LSST, well-matched wide-field
spectroscopic capabilities are desirable.
