COBE Constraints on Asteroidal Models of the Zodiacal Cloud

E.K. Holmes, S.F. Dermott, K. Grogan (University of Florida)

Using COBE 25 tex2html_wrap_inline14 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, tex2html_wrap_inline20 , is tex2html_wrap_inline22 , which is tex2html_wrap_inline24 of the value tex2html_wrap_inline26 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 tex2html_wrap_inline30 , which is significantly different from the longitude of the apocenter of the Earth's orbit, tex2html_wrap_inline32 . 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 tex2html_wrap_inline42 and compare them to the 25 tex2html_wrap_inline14 m waveband results.

This research was funded in part by a NASA GSRP grant.