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Meteor was there already before Riko joined WISE.
In my opinion that bonfire girl (also the lamp) is responsible for it, I think her ability is something like messing up ppl's fate and calling doom upon them.
Riko may have not created the meteor but I wouldn't be surprised if she had a major role in the usage of the Meteor's power in advantage of the wise. I don't think this meteor has been created by someone but it is used by evil psychicers (the wise) who must have been aware of the power hidden within the meteor. Bonfire probably predicted the impact of the meteor, Miroku probably talked with the meteor when he was part of the experiment, and so on and on
What people already said-The asteroid was around before WISE got Caprico.
Personally I think the personality that is Mithra/Bonfire has been around much longer than her body shows and she is potentially the spokesperson for Ouroboros
or even Ouroboros itself.