Very much as depicted earlier in concept art, these are several (seven or more) asteroid bases in a dusty, asteroid strewn level in the single-player campaign.

Another, somewhat different concept art referred to the asteroid base as "Gehenna".

These bases are Vaygr archeological dig sites, as Makaan's forces try to find the Oracle, an artifact that can help them to unlock the secrets of the ancient Progenitors.

Another biblical reference: Gehenna was the Hebrew "Place of Torment." The Valley of Hinnom, south-west of Jerusalem, where Solomon, king of Israel, built "a high place", or place of worship, for the gods Chemosh and Moloch. The valley came to be regarded as a place of abomination because some of the Israelites sacrificed their children to Moloch there. In a later period it was made a refuse dump and perpetual fires were maintained there to prevent pestilence. Thus, in the New Testament, Gehenna became synonymous with hell.