We present 2.3- to 18.5-μm photometry and 3- to 4-μm spectroscopy of Comet P/Encke that suggest that the comet develops a coma composed primarily of large grains when it is near perihelion. Our data show no evidence for the 3.4-μm hydrocarbon emission feature in P/Encke.
Bibliographical noteFunding Information:
We thank T. Brooke, D. Jewitt, and J. Luu for helpful comments. The University of Minnesota infrared astronomy program is supported by NASA, the United States Air Force, the National Science Foundation, and the University of Minnesota Graduate School. A. T. Tokunaga and E. Rosenthal acknowledge the support of NASA Contract NASW-3159; J. R. Piscitelli acknowledges the support of NASA NGL-12001-057. We thank W. Golisch of IRTF and L. R. Shaw of WIRO for their invaluable assistance at the telescope.