X-ray Fluorescence Nanotomography on Cometary Matter from Comet 81P/Wild2 Returned by Stardust

Using a significantly improved method for X-ray fluorescence (XRF) tomography with submicrometer spatial resolution, the fully three-dimensional (3D) distribution of main and brace elements from calcium to selenium was determined at a spatial resolution level of 200 nm within a unique (similar to 2 mu m) comet coma particle brought to Earth by the National Aeronautical and Space Administration (NASA)'s Stardust mission. The measurements were based on synchrotron radiation XRF nanotomography that has been applied to the terminal particle located in an aerogel host, which was used to capture comet and interstellar grain particles in space. Using a symmetric dual-detector arrangement for the presented nano-XRF tomography measurements, a rotation angle of 180 degrees was sufficient for the tomographic reconstruction. Dedicated correction algorithms were developed to correct for submicrometer-level distortions within the tomographic dataset arising from instabilities of the sample positioning system during data collection.