We present Hubble Space Telescope WFC3/IR images of the Cassiopeia A supernova remnant that survey its high-velocity , S-rich debris in the NE jet and SW counterjet regions through [ S iii ] \lambda \lambda 9069 , 9531 and [ S ii ] \lambda \lambda 10,287 – 10,370 line emissions .
We identify nearly 3400 sulfur emitting knots concentrated in \sim 120 { \arcdeg } wide opposing streams , almost triple the number previously known .
The vast majority of these ejecta knots lie at projected distances well out ahead of the remnant ’ s forward blast wave and main shell ejecta , extending to angular distance of 320 ^ { \prime \prime } to the NE and 260 ^ { \prime \prime } to the SW from the center of expansion .
Such angular distances imply undecelerated ejecta knot transverse velocities of 15,600 and 12,700 km s ^ { -1 } respectively , assuming an explosion date \approx 1670 AD and a distance of 3.4 kpc .
Optical spectra of knots near the outermost tip of the NE ejecta stream show strong emission lines of S , Ca , and Ar .
We estimate a total mass \sim 0.1 M _ { \odot } and a kinetic energy of at least \sim 1 \times 10 ^ { 50 } erg for S-rich ejecta in the NE jet and SW counterjet .
Although their broadness and kinetic energy argue against the Cas A SN being a jet-induced explosion , the jets are kinematically and chemically distinct from the rest of the remnant .
This may reflect an origin in a jet-like mechanism that accelerated interior material from a Si , S , Ar , Ca-rich region near the progenitor ’ s core up through the mantle and H , He , N and O-rich outer layers with velocities that greatly exceeded that of the rapidly expanding photosphere .