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It soon became clear to Afanasiev that this was no ordinary meteor. It hit the atmosphere at 300 kilometres per second, an order of magnitude faster than most other particles.
That’s puzzling. The Earth moves around the galactic center at about 220 km/s and so the meteor’s origin cannot easily be explained by reference to the Milky Way.
So where did it come from? Afanisiev and a few pals worked out that it appeared to come from the direction in which the Earth and the Milky Way is travelling towards the centre of our local group of galaxies. “This fact leads us to conclude that we observed an intergalactic particle, which is at rest with respect to the mass centroid of the Local Group and hich was “hit” by the Earth,” they say.