I'm on record as saying we will probably find evidence of life in the form of replicator chemistry (more common parlance, von Neumann probes) on asteroids and comets. My reasoning is here.
There was a recent paper in the Journal of Cosmology on this very topic which has come in for a good deal of bashing. Like many theories, my theory is a good story. But good stories are a dime a dozen. So now we need evidence to support or falsify the hypothesis.
Unfortunately, after this paper, we still have none.