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Spectroscopy from Rosetta has identified the make-up of a single dust grain captured by the spacecraft.
For the convenience of communications the science team had dubbed this single grain “Boris.”
[T]hese first results show that among the grain’s components are magnesium and sodium. Since 95 percent of the known observed minerals in comets resemble olivine and pyroxenes – containing a lot of magnesium – the detection of this element is not a big surprise. But, finding sodium in the dust grain, in a refractory mineral phase, has sparked our interest considerably.
The coma and tails of other comets are already known to contain sodium; it was observed in the dust samples returned from Comet Wild 2 by NASA’s Stardust mission, and a prominent example was also the sodium tail of Comet Hale-Bopp that flew past the Sun in April 1997 and which could be seen in the night sky for many weeks. However, by contrast, neither sodium nor magnesium were observed in Comet 67P/C-G dust grains before sampling the inner coma dust. But our dust grain Boris has showed off with clear sodium and magnesium mass peaks in the secondary ion mass spectra that we obtained.
Their next goal is to identify where on the surface of Comet 67P/C-G this sodium came from.