text: HCN has been detected in the interstellar medium and in the atmospheres of carbon stars. Since then, extensive studies have probed formation and destruction pathways of HCN in various environments and examined its use as a tracer for a variety of astronomical species and processes. HCN can be observed from ground-based telescopes through a number of atmospheric windows. The J=1→0, J=3→2, J= 4→3, and J=10→9 pure rotational transitions have all been observed.
  HCN is formed in interstellar clouds through one of two major pathways: via a neutral-neutral reaction (CH + N → HCN + H) and via dissociative recombination (HCNH + e → HCN + H). The dissociative recombination pathway is dominant by 30%; however, the HCNH must be in its linear form. Dissociative recombination with its structural isomer, HNC, exclusively produces hydrogen isocyanide (HNC).
  HCN is destroyed in interstellar clouds through a number of mechanisms depending on the location in the cloud. In photon-dominated regions (PDRs), photodissociation dominates, producing CN (HCN + ν → CN + H). At further depths, photodissociation by cosmic rays dominate, producing CN (HCN + cr → CN + H). In the dark core, two competing mechanisms destroy it, forming HCN and HCNH (HCN + H → HCN + H; HCN + HCO → HCNH + CO). The reaction with HCO dominates by a factor of ~3.5. HCN has been used to analyze a variety of species and processes in the interstellar medium. It has been suggested as a tracer for dense molecular gas and as a tracer of stellar inflow in high-mass star-forming regions. Further, the HNC/HCN ratio has been shown to be an excellent method for distinguishing between PDRs and X-ray-dominated regions (XDRs).
  On 11 August 2014, astronomers released studies, using the Atacama Large Millimeter/Submillimeter Array (ALMA) for the first time, that detailed the distribution of HCN, HNC, HCO, and dust inside the comae of comets C/2012 F6 (Lemmon) and C/2012 S1 (ISON).
  In February 2016, it was announced that traces of hydrogen cyanide were found in the atmosphere of the hot Super-Earth 55 Cancri e with NASA's Hubble Space Telescope.
  On 14 December 2023, astronomers reported the first time discovery, in the plumes of Enceladus, moon of the planet Saturn, of hydrogen cyanide, a possible chemical essential for life as we know it, as well as other organic molecules, some of which are yet to be better identified and understood. According to the researchers, "these [newly discovered] compounds could potentially support extant microbial communities or drive complex organic synthesis leading to the origin of life."