36.08-P
COBE Constraints on Asteroidal Models of the Zodiacal Cloud
E.K. Holmes, S.F. Dermott, K. Grogan (University of Florida)
Using COBE 25 
m waveband data, we have determined the variation
with the longitude of the Earth of the brightness of the zodiacal cloud
as seen at the North, N, and South, S, ecliptic poles. The extent
to which a purely asteroidal model of the zodiacal cloud can account
for these observations is investigated. We have determined from the
COBE data that the ratio of the amplitude of the variation with the
longitude of the Earth of the sum of the ecliptic brightnesses to the
mean value of this sum (averaged over all longitudes), that is,
, is 
, which is 
of the value 
determined from our asteroidal model.
This could be evidence for the loss of asteroidal dust with decreasing
heliocentric distance due to particle breakup. We have also determined
that the observed value of N + S is a minimum when the Earth has a
longitude of 
, which is significantly different
from the longitude of the apocenter of the Earth's orbit,
.
This could be evidence that the center of
symmetry of the zodiacal cloud is displaced from the Sun, in which
case our interpretation of the observed variation of N + S with
Earth's longitude needs further investigation. We compare COBE
observations with our model for four other mid infrared COBE wavebands:
4.9, 12, 60, and 
and compare them to the 25 m
waveband results.
This research was funded in part by a NASA GSRP grant.