It is often suggested that alien life could have reached Earth on a comet, but what about the other way around ? Scientists have long speculated over what processes might have given rise to life on other worlds. One such process, which is known as panspermia, involves life from one planet being transported to another on asteroids and comets that have come into contact with an inhabited world. While this theory is often put forward as an answer to how life on our own planet first emerged, comparatively little thought is given to the idea that this may have happened the other way around. Could ancient microbes from Earth have hitched a ride to a planet in some distant solar system? According to astrophysicists Amir Siraj and Avi Loeb, such a scenario is actually possible. The pair theorize that in Earth's distant past, a large, fast-moving comet could have grazed our planet's atmosphere, picking up microbes that became embedded deep within its surface. If any of these managed to survive