Scientists say they've found the best evidence yet for panspermia - the theory that life on Earth developed from microorganisms brought here from other planets on asteroids, meteors and the like.
Previous research had suggested that the high speed at which objects move through space made the chance of them being captured by another planet very small.
However, this new research, based on computer simulations of the star cluster our sun was born in, suggests that a process called weak transfer - in which solid objects can gradually meander out of the orbit of one object and into another - greatly increase the odds that this process could have happened.
"Our work says the opposite of most previous work," says mathematician Edward Belbruno of Princeton University. "It says that lithopanspermia might have been very likely, and it may be the first paper to demonstrate that. If this mechanism is true, it has implications for life in the universe as a whole. This could have happened anywhere."
The researchers reckon that the solar system and its nearest planetary-system neighbour could have swapped rocks at least 100 trillion times before the sun left its native star cluster. And rock evidence shows that basic life forms could indeed date from that far back.
"The conclusion from our work is that the weak transfer mechanism makes lithopanspermia a viable hypothesis because it would have allowed large quantities of solid material to be exchanged between planetary systems, and involves timescales that could potentially allow the survival of microorganisms embedded in large boulders," says astronomer Amaya Moro-Martín.
"The study of the probability of landing on a terrestrial planet is work that we now know is worth doing, because large quantities of solid material originating from the first planetary system may be trapped by the second planetary system, waiting to land on a terrestrial planet."