How should I stat very powerful artifacts that the party acquires too early?

A few weeks ago I started DMing a campaign that involves five divine artifacts that all of the gods’ powers are filtered through. I planned on the paragon level quest being collecting these in order to either destroy or protect them. Unfortunately, one of my players rolled a natural 20 on Thievery to steal the chestplate artifact at Level 2 (next encounter will level them up). How should I handle the stats on this item?