Something interesting occurred in the late 1960’s as part of the Apollo program. The uncrewed probe Surveyor 3 was landed in the Ocean of storms in 1967. Part of the Apollo 12 mission, the second crewed landing in 1969, was to retrieve engineering samples from Surveyor 3. That mission was a success, but that is only the beginning of the story.
For two years, Surveyor had unintended passengers waiting on the surface of the Moon for 31 months. They were bacteria spores that managed to survive in the vacuum of space. The very fact of their survival begs the question: Are their natural processes that can move life from one planet to another over interplanetary distances? And if that is possible: Is it possible for those same processes to move life interstellar distances?
Recently, an additional piece to the panspermia story was added. An object passed through the solar system. The trajectory of the object confirmed that it was interstellar in origin. It is called Oumuamua. Models have suggested that there might be 10 million such objects nearby the sun (see Our Solar System… from inverse). With that many objects we likely have samples from 10 million stars from around the Milky Way. Similarly, we could have sent samples to around the same number of stars.
Taking a page from the Drake Equation, we can look at a probability of obtaining a sample of life from another life bearing planet. Number of objects , times the probability of planets per system , times the number of planets per system , times the probability of a planet having life , times the probability the sample survived the journey should give us the number of live samples that could be within reach: .