SILICATE EMISSION FEATURE IN THE SPECTRUM OF COMET MUELLER 1993A

An 8- to 13-mu m spectrum of comet Mueller 1993a, a dynamically new co met, was acquired when the comet was at R = 2 AU. Strong, structured s ilicate emission is present, closely resembling that seen in Comet P/H alley at smaller R. For the first time in a new comet, the 11.2-mu m p eak of crystalline olivine was detected, demonstrating that crystallin e olivine particles were widespread in the solar nebula. Crystalline o livine particles could have formed in the inner protosolar nebula at t emperatures greater than 1200 K; extensive radial mixing would have be en required to transport these grains to the region of comet formation . Either there was more radial mixing in the solar nebula than some cu rrent theories predict or the olivine grains have a presolar origin. ( C) 1994 Academic Press, Inc.