  This paper investigates whether an isotropic zodiacal light from the outer
Solar system can account for the detected background excess in near-infrared.
Assuming that interplanetary dust particles are distributed in a thin spherical
shell at the outer Solar system (>200 AU), thermal emission from such cold (<30
K) dust in the shell has a peak at far-infrared (~100 microns). By comparing
the calculated thermal emission from the dust shell with the observed
background emissions at far-infrared, permissible dust amount in the outer
Solar system is obtained. Even if the maximum dust amount is assumed, the
isotropic zodiacal light as the reflected sunlight from the dust shell at the
outer Solar system cannot explain the detected background excess at
near-infrared.
