On earth, and possibly the moon, a pop up will appear where it says "a band of pikes" or "ZireRanger died", it can say "the minions of Crota are preforming a ritual. Then a "blade of Crota" level 10 knight came out. Killing him will allow you to pick up and use his sword. Once you pick up the sword, it will say "ZireRanger has acquired the sword".