COBE DIRBE NEAR-INFRARED POLARIMETRY OF THE ZODIACAL LIGHT - INITIAL RESULTS

This Letter describes near-infrared polarimetry of the zodiacal light at 2.2 mum, measured with the Diffuse Infrared Background Experiment ( DIRBE) aboard the Cosmic Background Explorer (COBE) spacecraft. The po larization is due to scattering of sunlight. The polarization vector i s perpendicular to the scattering plane, and its observed amplitude on the ecliptic equator at an elongation of 90-degrees and ecliptic long itude of 10-degrees declines from 12.0 +/- 0.4% at 1.25 mum to 8.0 +/- 0.6% at 3.5 mum (cf. 16% in the visible); the principal source of unc ertainty is photometric noise due to stars. The observed near-infrared colors at this location are redder than Solar, but at 3.5 mum this is due at least in part to the thermal emission contribution from the in terplanetary dust. Mie theory calculations show that both polarization s and colors are important in constraining models of interplanetary du st.