The Unusual Volatile Composition of the Halley-Type Comet 8P/Tuttle: Addressing the Existence of an Inner Oort Cloud

Abstract

We measured organic volatiles (CH4, CH3OH, C2H6, H2CO), CO, and water in comet 8P/Tuttle, a comet from the Oort Cloud reservoir now in a short-period Halley-type orbit. We compare its composition with two other comets in Halley-type orbits, and with comets of the "organics-normal" and "organics-depleted" classes. Chemical gradients are expected in the comet-forming region of the protoplanetary disk, and an individual comet should reflect its specific heritage. If Halley-type comets came from the inner Oort Cloud as proposed, we see no common characteristics that could distinguish such comets from those that were stored in the outer Oort Cloud. © 2008. The American Astronomical Society. All rights reserved. Printed in U.S.A.