Mapping trace elements within a grain of stardust

The challenge
To determine the 3D distribution of main and trace elements in a cometary dust particle embedded in an aerogel matrix.

Background
The NASA Stardust mission captured extremely precious cometary dust particles and returned them to Earth. The particles were captured in space using an aerogel matrix to stop and trap the dust particles. The terminal particles captured are around 2 micrometres in size.

Results
Fully 3D, non-destructive, trace-level elemental imaging was made on a dust particle showing the distribution of elements from calcium to selenium at sub-micrometre (200 nm) spatial resolution.

How did the synchrotron help?
X-rays are an element-selective, non-destructive probe. The very fine X-ray beams available on beamline ID13 (the ESRF pilot project for further nano-focus X-ray beams), enabled nanotomographic images of the minute cometary dust particles to be recorded and transformed into the full 3D reconstruction.

Figure 1. The reconstructed comet dust particle with colours showing the distribution of different elements (red: iron; green: chromium; blue: selenium).

Reference
X-ray Fluorescence Nanotomography on Cometary Matter from Comet 81P/Wild2 Returned by Stardust, G. Silversmit, B. Vekemans, F.E. Brenker, S. Schmitz, M. Burghammer, C. Riekel, and L. Vincze, Anal. Chem. 81, 6107–6112 (2009).