Time-Domain Photometry of Protostars at Far-Infrared and Submillimeter
  Wavelengths
  The majority of the ultimate main-sequence mass of a star is assembled in the
protostellar phase, where a forming star is embedded in an infalling envelope
and encircled by a protoplanetary disk. Studying mass accretion in protostars
is thus a key to understanding how stars gain their mass and ultimately how
their disks and planets form and evolve. At this early stage, the dense
envelope reprocesses most of the luminosity generated by accretion to
far-infrared and submillimeter wavelengths. Time-domain photometry at these
wavelengths is needed to probe the physics of accretion onto protostars, but
variability studies have so far been limited, in large part because of the
difficulty in accessing these wavelengths from the ground. We discuss the
scientific progress that would be enabled with far-infrared and submillimeter
programs to probe protostellar variability in the nearest kiloparsec.
