A LDE experiment has provided Diamond’s Christmas image this year. It’s examining the slow in situ precipitation of meridianiite, a hydrated magnesium sulfate mineral. Meridianiite is named for Meridiani Planum. In 2007 the Mars rover Opportunity observed crystal moulds in the sedimentary rock there, and these are thought to be caused by minerals that have since dehydrated or dissolved. Researchers investigating whether Mars once harboured life are very interested in the planet’s hydrological history, and want to know how much water remains on the surface of Mars and how it is being held – for example, in hydrated minerals such as meridianiite.