Earth's transmigration plans require finding a planet whose environment resembles its own, which is reasonably safe to live on, and which does not harbor indigenous life that would be harmed by an influx of humans. After a long period of earthbound observation and exploration, several Earth-like planets were found within five light years of its own solar system, but these were later deemed unsuitable for terraforming due to the presence of hostile life forms or previously-unknown viruses.