Editorials

The Central Andes is a land of llamas, salt flats and majestic volcanic peaks. It is one of most remote places on Earth and arguably the driest. In a not unconnected way, the Central Andes is also home to the world’s largest copper mines. The unique combination of magmas, tectonics and climate, described in this issue of Elements, has conspired to create hydrothermal ore deposits that provide a third of the world’s copper and a quarter of its molybdenum.

As we set up the publication schedule for each year, the principal editors of Elements try to ensure that the journal maintains enough diversity to hold the interest of you, our readers. In this context, we sometimes accept proposals for issues on very well-known mainstream subjects (such as layered intrusions) which we think can usefully be updated and summarised at a good level. We also try, however, to bring you subjects which are outside the mainstream yet still can be grouped loosely within the areas of geochemistry, mineralogy and petrology. That is how we categorise the current issue dealing with the environmental aspects of making high-quality wine.

The articles in this “Comets” issue of Elements provide a fascinating account of comets and the making of our planetary system. We learn why comets are visible to the naked eye and about their complex organic geochemistry, the surprising find of free O2, and the likelihood of a comet impact on Earth. Perhaps most impressively, we learn about the tremendous effort that goes into the exploration of comets. These missions require decades of design, planning, and instrument miniaturization and their culmination captures our imagination in a way little else can. Who could not be enthralled by the evocatively named Stardust mission returning a few thousand grains of dust from comet Wild 2 to Earth? We collectively shared the despair when communication was lost from Rosetta’s Philae lander on comet 67P/Churyumov–Gerasimenko, and the excitement about the unparalleled wealth of information sent back during its 70 hours of life on the comet’s surface.