Observations of Interstellar Formamide: Availability of a Prebiotic Precursor in the Galactic Habitable Zone

Abstract

We conducted a study on interstellar formamide, NH₂CHO, toward star-forming regions of dense molecular clouds, using the telescopes of the Arizona Radio Observatory (ARO). The Kitt Peak 12 m antenna and the Submillimeter Telescope (SMT) were used to measure multiple rotational transitions of this molecule between 100 and 250 GHz. Four new sources of formamide were found [W51M, M17 SW, G34.3, and DR21(OH)], and complementary data were obtained toward Orion-KL, W3(OH), and NGC 7538. From these observations, column densities for formamide were determined to be in the range of 1.1×10¹² to 9.1×10¹³ cm⁻², with rotational temperatures of 70–177 K. The molecule is thus present in warm gas, with abundances relative to H₂ of 1×10⁻¹¹ to 1×10⁻¹⁰. It appears to be a common constituent of star-forming regions that foster planetary systems within the galactic habitable zone, with abundances comparable to that found in comet Hale-Bopp. Formamide's presence in comets and molecular clouds suggests that the compound could have been brought to Earth by exogenous delivery, perhaps with an infall flux as high as ∼0.1 mol/km²/yr or 0.18 mmol/m² in a single impact. Formamide has recently been proposed as a single-carbon, prebiotic source of nucleobases and nucleic acids. This study suggests that a sufficient amount of NH₂CHO could have been available for such chemistry. Key Words: Formamide—Astrobiology—Radioastronomy—ISM—Comets—Meteorites. Astrobiology 13, 439–453.