A new study from Penn State has found that life on other planets, should it exist, may have stemmed from Earth’s ancient lineages. According to the study, published last week in Astrobiology, following dramatic collisions, like the impact that created the Chicxulub crater in Mexico and led to the mass extinction of the dinosaurs, Earth has ejected a pretty large number of meteorites capable of carrying life to any of the terrestrial planets in the Solar System as well as to Jupiter (which isn’t terrestrial; they could reach Saturn as well, but it’s not as likely).
The group estimates that Earth has cast out 26 million meteorites capable of reaching Venus, 730,000 that could have hit Mercury, 360,000 capable of seeding Mars, and 83,000 to Jupiter (Saturn only managed 14,000, hence their argument that it’s more unlikely life from Earth managed to reach there). They also found that factors like speed and direction only affected whether or not a meteorite would return to Earth, not whether it would hit another planet.
Panspermia, the transfer of life between planets, isn’t a new idea. Nor is lithopanspermia, where that transfer occurs via rocks getting thrown around after serious impacts. According to the authors of the study, there are even some theories that argue life on Earth originated from meteorites ejected from Mars. The possibility of interplanetary exchange of life has been discussed since the mid-seventies and a surprising amount of work has been done trying to figure out what exactly would be necessary for life to survive a trip through space; apparently all you need is a rock at least 3 m. in diameter to sufficiently protect Deinococcus radiodurans from the cold realities of space. It is worth noting that D. radiodurans is a ridiculously hardy extremophile bacterium that can survive cold, dehydration, radiation, vacuum, and acid. Seriously, I’m pretty sure this thing is invincible.
While the idea that life on other planets may have begun here on Earth isn’t new, the level of detail in this study is. The group was able to estimate how often meteors from earth capable of harboring life would have reached every planet in the Solar System and even some of Saturn’s and Jupiter’s moons. What this ends up showing is how likely it is that life found on these planets would be in some way connected to life here. As missions begin reaching further and further into our Solar System and the possibility of discovering new life becomes more science and less science fiction, scientists must remember that these may not necessarily represent isolated evolutionary timelines, but could share their remote ancestors with Earth’s myriad life forms. Which definitely sounds like science fiction.
(I feel the need to mention here that for whatever reason, the Solar System as defined by this study’s work seems to stop after Saturn, excluding Uranus and Neptune. From what I can tell, it’s because previous work with interplanetary transfer via meteorite collisions was pretty much nonexistent in the outer planets)