While one of curium's isotopes has a very long half-life relative to its neighbours – Cm-247 at 15.6 million years – it is not the one most often used. That title goes to Cm-244, the source for alpha particle X-ray spectrometers on Martian rovers like Curiosity, which is why Rainbow Dash is here. She is perching over Rocknest 3, which was examined by Curiosity's APXS in October 2012.

SVG here.