The small probes travel at and perform fly-by investigations. If a probe detects intelligent life it lets the home planet know; if it detects nothing it moves on to the next unexplored star. Once the probes have visited all 40,000 stars on the list they return to the host, which moves to a new destination star and the exploration process starts afresh. Using this method of exploration, Bjørk found that it would take about 300 million years to explore just 4 % of the Galaxy.
Wow
