How Steins’ craters got gemstone names

Tweet Guest post by Sebastien Besse, Research Fellow at ESTEC On 5 September 2008, ESA’s Rosetta comet chaser completed its first encounter with a main belt asteroid when it flew past Steins, which revealed itself as a diamond-shaped object with dimensions of 6.67 × 5.81 × 4.47 km. At the time, I was a PhD student working with the OSIRIS imaging team in France studying the craters on Steins. With the asteroid’s diamond shape for inspiration, I began to think about naming the craters after different gemstones. I tried to select names that would be familiar or appealing to the general public, and easy to pronounce. As is the case with the official place names given to all worlds in the Solar System, they have to be approved by the International Astronomical Union (IAU). We had quite some discussions because we had to choose names of gems or precious minerals/stones that would not be confusing for studying the true mineralogy of the asteroid’s surface. In the end, the OSIRIS imaging team agreed that the names of 23 gemstones or precious minerals would be recommended to the IAU. To date, about 40 craters have been identified on Steins, but only the most prominent of them have been given names. In some cases we tried to name craters geographically close to each other with names from the same gemstone family. So for example, Aquamarine and Emerald are both from the Beryl family of gemstones, and Agate, Amethyst and Citrine are all types of quartz. Another example is that the crater Alexandrite sits inside the crater named Chrysoberyl – I named them like this because Alexandrite is a type of Chrysoberyl. The most obvious crater is an impact feature near the south pole (top in the images) – now known as Diamond crater […]



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