Some of these celestial bodies occasionally appear as comets with unexpected orbits bringing them close to our star, where they can get gravitationally influenced by planets all the way out of the Solar System.
Those asteroid approaching Earth, passing just 30 to 60 miles (50 to 100km) above the surface would theoretically be capable of collecting life from the atmosphere.
While the abundance of microbes in the uppermost atmosphere is poorly constrained, it is well known that microorganism colonies exist at such altitudes.
Professor Loeb wrote: “In a new paper written with my undergraduate student Amir Siraj, we calculate that there could have been tens of such life-exportation events over the lifetime of Earth.
“A similar number of events are expected to be associated with asteroids that came from outside the Solar System before they grazed our planet’s atmosphere.