Formaldehyde in comets C/1995 O1 (Hale-Bopp), C/2002 T7 (LINEAR), and C/2001 Q4 (NEAT): Investigating the cometary origin of H2CO

Stefanie N. Milam, Anthony J. Remijan, Maria Womack, Leif Abrell, L. M. Ziurys, Susan Wyckoff, A. J. Apponi, D. N. Friedel, L. E. Snyder, J. M. Veal, Patrick Palmer, L. M. Woodney, Michael F. A'Hearn, J. R. Forster, M. C.H. Wright, I. De Pater, S. Choi, M. Gesmundo

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35 Scopus citations


Observations of formaldehyde (H2CO) have been conducted toward comets C/1995 O1 (Hale-Bopp), C/2001 Q4 (NEAT), and C/2002 T7 (LINEAR) using the Arizona Radio Observatory (ARO) 12 m telescope at 1.2 and 2 mm. Aperture synthesis maps of H2CO at 3 mm were made using the Berkeley-Illinois-Maryland Association (BIMA) interferometer toward comet Hale-Bopp. These data indicate that the production rate of H2CO is ∼3.7 × 1028 s-1 at ∼1 AU in comet Hale-Bopp, using a simple Monte Carlo model, if a nuclear origin for the molecule is assumed. However, maps of H2CO in Hale-Bopp, in comparison with CO, show an extended distribution (rs ∼ 15,000 km) with small-scale structure oriented roughly along the comet-Sun direction. This result suggests a source of H2CO other than the comet nucleus. The extended source of formaldehyde is probably grains composed of a mixture of silicates and organic material. The production rate for H2CO increases to Q ∼ 1.4 × 1029 s-1 assuming such an extended grain source. This value implies a Q/Q(H2O) ∼ 1.4%, which is similar to the production rate ratio of Q/Q(H2O) ∼ 4% derived from in situ measurements of H2CO in comet Halley. Production rates for H 2CO toward comets C/2002 T7 (LINEAR) and C/2001 Q4 (NEAT) are 1.4 × 1027 and 5.6 × 1026 s-1, respectively, modeled using the extended grain source. The spectra of H 2CO measured toward comet C/2002 T7 (LINEAR) show evidence for a second velocity component, most likely arising from comet fragmentation.

Original languageEnglish (US)
Pages (from-to)1169-1177
Number of pages9
JournalAstrophysical Journal
Issue number2 I
StatePublished - Oct 1 2006


  • Astrobiology
  • Comets: individual (Hale-Bopp (C/1995 O1), NEAT (C/2001 Q4), LINEAR (C/2002 T7))
  • Radio lines: solar system
  • Techniques: interferometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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