Welcome in another year of musical theatre with a show that has a rather. distinct name. The satirical comedy musical Urinetown is headed to Sydney at the
Comet Lovejoy. Image credit: John Vermette (photographer).
### Photodissociation and comet colors
Unlike the tail of a comet, the coma, a nebulous envelope around the solid, central part of the comet, is often green. This phenomenon is explained by the destruction of the molecule C2 by sunlight through a process called photodissociation, but the mechanism is unclear. Using velocity map imaging and multiphoton ionization, Jasmin Borsovszky et al. directly observed C2 photodissociation in the laboratory, revealing the mechanism by which sunlight destroys C2 in comets. Based on the speed of the recoiling carbon atoms, the authors precisely calculated the bond dissociation energy (BDE), or the strength of the chemical bond, of C2 to be 602.782(29) kJ mol−1, making the uncertainties of the BDEs comparable for C2 and its more experimentally accessible counterparts N2 and O2. Consistent with astronomical observations, the authors calculated the lifetime of cometary C2 to be 1.6 × 105 s