ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP): Evidence for
  a Molecular Jet Launched at an Unprecedented Early Phase of Protostellar
  evolution
  Protostellar outflows and jets play a vital role in star formation as they
carry away excess angular momentum from the inner disk surface, allowing the
material to be transferred toward the central protostar. Theoretically, low
velocity and poorly collimated outflows appear from the beginning of the
collapse, at the first hydrostatic core (FHSC) stage. With growing protostellar
core mass, high-density jets are launched which entrain an outflow from the
infalling envelope. Until now, molecular jets have been observed at high
velocity ($\gtrsim$ 100 km/s) in early Class\,0 protostars. We, for the first
time, detect a dense molecular jet in SiO emission with small-velocity ($\sim$
4.2 km\,s$^{-1}$, deprojected $\sim$ 24 km\,s$^{-1}$) from source
G208.89-20.04Walma (hereafter, G208Walma) using ALMA Band\,6 observations. This
object has some characteristics of FHSCs, such as a small outflow/jet velocity,
extended 1.3\,mm continuum emission, and N$_2$D$^+$ line emission. Additional
characteristics, however, are typical of early protostars: collimated outflow
and SiO jet. The full extent of the outflow corresponds to a dynamical time
scale of $\sim$ 930$^{+200}_{-100}$ years. The spectral energy distribution
also suggests a very young source having an upper limit of T$_{bol}$ $\sim$ 31
K and L$_{bol}$ $\sim$ 0.8 L$_\sun$. We conclude that G208Walma is likely in
the transition phase from FHSC to protostar, and the molecular jet has been
launched within a few hundred years of initial collapse. Therefore, G208Walma
may be the earliest object discovered in the protostellar phase with a
molecular jet.
