9520797 Womack It has been hypothesized that short-period comets and giant comets (like Chiron and SW1) share a common origin in the Kuiper Disk located 10-100 Astronomical Units (AU) from the Sun. Interestingly, recent observations indicate that these two populations of Kuiper disk comets may exhibit very different physical and chemical behavior. For example, short-period comets are small in size ranging from 1-10 km in diameter, and are predominantly water ice and so sublimate mostly within 1-2 AU from the Sun; while the giant comets are > 10 times larger than short-period comets, sublimate at larger distances from the Sun (r > 5 AU) and hence are thought to be comprised of some other highly volatile ice (quch as methane, carbon monoxide or Nitrogen). Current models of the protosolar nebula indicate that the chemical behavior of the dominant carbon-bearing molecules carbon monoxide, formaldehyde, methanol, and hydrogen cyanide are very sensitive to the physical and chemical processes that occurred during solar system formation. Therefore, the relative abundances of these species in primitive icy bodies, such as comets, are expected to place powerful constraints on comet-formation models. Comparison of these molecular abundances in the two populations of comets are, therefore, vital in testing models of the Kuiper disk region of the solar nebula. Observations of the rotational spectra of emissions from carbon monoxide, formaldehyde, methanol and hydrogen cyanide will be obtained of comets using millimeter and submillimeter wavelength telescopes. Complementary observations will be obtained and optical imaging techniques will be used in interpreting the spectra. A fundamental goal of this research is to make an exploratory comparison of carbon chemistry in several short-period comets with that in two large, distant comets. This work will search for chemical differences between these two groups to examine whether or not they are really two distinct divisions , or instead are better described by a continuous distribution of different chemical compositions. The work will help establish the feasibility of the proposed observations, determine which molecules are the best for testing models, and determine how often the large continuously active comets need to be observed in order to significantly constrain models of solar system formation.
