On the space oriented bbs uplink.space.com someone mentioned the detections of olivine in Tempel I and previously in other comets raise the possibility of more heating in comets than would be expected for objects formed far from the Sun. This would also be consistent with the theory of radiogenic heating in comets:

NASA Research Finds Green Sand Crystals Are in Comet Tempel 1.
Date Released: Thursday, September 15, 2005
http://spaceflightnow.com/news/n0007/20cometdust/

Time travel through a trail of comet dust.
NASA/GSFC NEWS RELEASE
Posted: July 20, 2000.
"We know that these dust grains change from amorphous to crystalline as they are heated, and our laboratory research revealed that the rate at which they change is extremely sensitive to temperature," Nuth added. "At the very low temperatures, where water-ice and the other volatile components of comets are frozen, the time required for amorphous silicate dust grains to change to the crystalline olivine found in comet Halley is many times longer than the age of the Universe."
http://spaceflightnow.com/news/n0007/20cometdust/

So there at least three separate and independent indications of internal heating, likely radiogenic, in comets: carbonate/clay detected in Tempel I, olivine in Tempel I and other comets, and crystalline ice detected deep in the Kuiper belt:

Chilly Quaoar had a warmer past.
Mark Peplow
Crystalline ice suggests remote object has radioactive interior.
Published online: 8 December 2004.
http://www.nature.com/news/2004/041206/pf/041206-7_pf.html

The existence of such heating had been theorized to permit liquid water in
comets which with the abundance of organics in comets raises the possibility of life.

Bob Clark

cf.:

Carbonate and clay in comet Tempel I raises the possibility of life.
Posted by Robert Clark on 9/7/2005 5:18:57 PM
http://habitablezone.com/space/messages/394880.html