Space debris in near-Earth orbit

Debris: Iridium 33

Fragments of the working communications satellite Iridium 33, the other side of the 2009 collision; there are fewer of them than of Cosmos 2251 because it was the lighter of the two

The other side of the 2009 collision: Iridium 33 was a working satellite of the Iridium constellation, and it was lost outright. Its fragments are catalogued separately from Cosmos 2251’s, which is how the two clouds can be told apart at all - they were left in the same place at the same instant.

Further reading: orbitaldebris.jsc.nasa.gov