The late Nobel prize winner Professor Francis Crick, OM FRS, along with British chemist Leslie Orgel proposed the theory of directed panspermia in 1973. A co-discoverer of the double helical structure of the DNA molecule, Crick found it impossible that the complexity of DNA could have evolved naturally.
Crick posed that small grains containing DNA, or the building blocks of life, could be loaded on a brace of rockets and fired randomly in all directions. Crick and Orgel estimated that a payload of one metric ton could contain 1017 micro-organisms organized in ten or a hundred separate samples. This would be the best, most cost effective strategy for seeding life on a compatible planet at some time in the future.
The strategy of directed panspermia may have already been pursued by an advanced civilization facing catastrophic annihilation, or hoping to terraform planets for later colonization.