Obviously you don't want to be breathing HCN (hydrogen cyanide gas). However CN represents a big problem for designing heat shields. CN is sometimes called "cyanogen" but the chemists poo-poo that saying cyanogen is actually C2N2. CN, NO, CO are examples nonsymmetric diatomic molecules. Nonsymmetric diatomic molecules are very efficient at transforming thermal energy into radiative heat flux. The problem of thermal radiation due to diatomic molecules has been perplexing heat shield designers for decades. The main bad boy with air is typically NO. CN becomes a trouble maker for terrestrial hypersonic entry if the heat shield is a carbon based ablator. CN is a problem for Mars entry if the entry velocity gets over 7 km/sec or the nose radius is really big, e.g. a manned vehicle. The level of CN radiation for Huygens is a ***Big Issue***. People are worried. The level of radiative heat flux due to CN can vary by an order-of-magnitude due to methane concentrations in Titan's atmosphere and the altitude of Huygens during peak heat flux. A nonintuitive aspect about CN radiation is it can be reduced by going into the atmosphere faster. The trick is to have peak heat flux occur at an altitude and atmospheric density where the CN dissociates into gaseous carbon and atomic nitrogen (poor radiators). Of course, you need to have a really good atmospheric model to design the trajectory (we don't have that for Titan). This is one of the many reasons why it is vital for Huygens to succeed. We really do need that in-situ based atmospheric model for future Titan missions.

Gary