The unusual volatile composition of the Halley-type comet 8P/Tuttle:   Addressing the existence of an Inner Oort Cloud
  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 proto-planetary 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. 
H. Boehnhardt, M. J. Mumma, G. L. Villanueva, M. A. DiSanti, B. P.   Bonev, M. Lippi, H. U. Kaeufl