Sagan ‘studied’ the problem of interplanetary/interstellar radiation acting as a sterilizing agent on any microbes hitching rides through space (not inside meteoritic material), and concluded (with his coauthor, who probably did all the work) that panspermia wouldn’t occur. Organic material (molecules with carbon-hydrogen bonds, whatever their origin, are organic, for those who dunno) is found on meteorites.
The Origins of Directed Panspermia
[molybdenum connection]
http://blogs.scientificamerican.com/guest-blog/2013/01/09/the-origins-of-directed-panspermia/
http://en.wikipedia.org/wiki/Panspermia
The Big Splash is worth checking out:
Small Comets and Our Origins
http://www.freerepublic.com/focus/bloggers/1250694/posts
At the very least, at the current rate of arrival, all the water on Earth must have come from small comets hitting the atmosphere. And if the general idea of the nebular hypothesis is correct, the impact rate must have been much higher at one time.
There was no asteroid planet, as far as I’m concerned, but here’s three topics relevant to that:
Long-Destroyed Fifth Planet May Have Caused Lunar Cataclysm, Researchers Say
http://www.freerepublic.com/focus/news/653287/posts
An Unknown Planet Orbits in the Outer Solar System
http://www.freerepublic.com/focus/chat/1876853/posts
Red Planet’s Ancient Equator Located
http://www.freerepublic.com/focus/chat/1390424/posts