Dr Gladman's team calculated that up to 20 terrestrial rocks from a large impact on Earth would reach Titan. These would strike Titan's upper atmosphere at 10-15 km/s. At this velocity, the cruise down to the surface might be comfortable enough for microbes to survive the journey.But the news was more bleak for Europa. By contrast with the handful that hit Titan, about 100 terrestrial meteoroids hit the icy moon.

"It's frustrating if you're a microbe that's been wandering the Universe for a million years to then die striking the surface of Europa," Dr Gladman mused.Asked after his presentation by one scientist whether he thought microbes would be able to survive Titan's freezing temperatures, Dr Gladman answered: "That's for you people to decide, I'm just the pizza delivery boy."

This panspermia idea: does it or could it fit in with a broader understanding of evolution, such that life spreading through space in a potential form as embedded microbes may, somewhat randomly, hit upon an organically 'fertile' body and seed it?