CK Vul: a smorgasbord of hydrocarbons rules out a 1670 nova (and much else besides)

We present observations of CK Vul obtained with the Spitzer Space Telescope. The infrared spectrum reveals a warm dust continuum with nebular, molecular hydrogen and HCN lines superimposed, together with the `Unidentified Infrared' features. The nebular lines are consistent with emission by a low-density gas. We conclude that the Spitzer data, combined with other information, are incompatible with CK Vul being a classical nova remnant in `hibernation' after the event of 1670, a `very late thermal pulse', a `Luminous Red Variable', such as V838 Mon, or a `diffusion-induced nova'. The true nature of CK Vul remains a mystery.