Vol. 544
In section 1. Letters to the Editor

Herschel measurements of the D/H and 16O/18O ratios in water in the Oort-cloud comet C/2009 P1 (Garradd)

Using Herschel observations of water lines around 500GHz, Bockelée-Morvan et al. find that comet Garradd (also named C/2009 P1) is characterized by a low D/H value. The ratio of deuterium to hydrogen in water ice is a tracer of the thermodynamical conditions in which the ices were formed and of the amount of mixing that took place. It had been proposed that comets were pristine bodies that had a high, well-defined, almost primordial D/H ratio. This finding demonstrates once more that this idea is not in line with observations and that models of the formation of the solar system have to account for the very diverse population of comets.