Actually, the data is consistent with a dirty snowball, or an icy dirtball.<br /><br />What was surprising was that the "dust or dirt" showed signs of being heated far above the temperatures expected out in the repositories where comets are thought to have formed.<br /><br />So the unexpected and surprising part has more to do with the early development of the solar system than the comets themselves.<br /><br />The images of comet nuclei are pretty consistent with what we expected, especially after our first close up of Halley's comet.<br /><br />The ice/dust/dirt micture is covered by a cohesive surface of material that has been modified by it's long time on the surface interacting with the solar wind, UV radiation, meteoroid impacts, and cosmic rays.<br /><br />Through that surface, jets eject material, as the ices beneath reach a temperature where they sublimate (turn from solid to gas) and pass through a crack, or hole melted through the surface.<br /><br />One other thing to remember is that we have learned over the last few decades is that there is a huge variety of small solar system objects, from solid iron, to solid rock, to porous rubble piles, and widely varying percentages of various ices. It's a continuum. There are not just asteroids and comets; there is no sharp dividing line between them.<br /><br />An object might appear like an asteroid far from the sun, but get it close enough to warm, and voila, it's a comet. There are a few known comets that reside totally within the asteroid belt; comet Holmes is but one example.<br /><br />It's all a part of learning about our solar system, which is why Dawn, New Horizons (it's been said Pluto would just be a really big comet if it was closer to the sun), Rosetta, and many other missions will continue our educational process.<br /><br />Now that's SCIENCE <img src="/images/icons/smile.gif" /> <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>