Fellow PSU Astro grad Rachel Worth recently published a paper in Astrobiology, in which she studied what happens to rocks that are ejected into space by asteroid impacts on Earth. Big impacts like these are not infrequent on geologic timescales, and were even more common in the early days of the Solar System. Most impacts likely launch a fair amount of rock into space. Some of this rock falls back to Earth, some will escape Earth's orbit, and some will travel to other planets or moons, where it might crash-land and survive (if it is big enough!). Rachel simulated a set of impacts on Earth and watched to see where the debris would end up in the Solar System.
Astrobiologically speaking, the important point is that if the ejected rocks are big enough (~3m), hardy forms of life might be able to hitch a ride. The punchline of Rachel's study is that it is likely that some of these big rocks from Earth have landed on other planets and moons in the Solar System - some of which may have (or have had in the past) the necessary conditions for habitability. Lithopanspermia is the hypothetical process of spreading life among planets through these types of impacts.
Is it possible that life could have spread from Earth through interplanetary space? Or to Earth from elsewhere? With a better sense of how asteroid debris could offer interplanetary "shuttles" for some (probably quite confused) life forms, it definitely seems possible!
Check out the cool BBC article about Rachel's work, and the Astrobites writeup as well. The paper itself is available on arXiv.
