  Even at extragalactic distances, the shape of supernova ejecta can be
effectively diagnosed by spectropolarimetry. We present here results for 17
Type Ia supernovae that allow a statistical study of the correlation among the
geometric structures and other observable parameters of Type Ia supernovae.
These observations suggest that their ejecta typically consist of a smooth,
central iron rich core and an outer layer with chemical asymmetries. The degree
of this peripheral asphericity is correlated with the light-curve decline rate
of Type Ia supernovae. These observations lend strong support to
delayed-detonation models of Type Ia supernovae.
