As astronomical techniques become more advanced, a team of astrophysicists think they will be able to not only detect the signatures of alien life in exoplanetary atmospheres, but also track its relentless spread throughout the galaxy.
The research, headed by Henry Lin of the Harvard-Smithsonian Center for Astrophysics (CfA), assumes that this feat may be possible in a generation or so and that the hypothesis of panspermia may act as the delivery system for alien biology to hop from one star system to another.
Panspermia is a process where life is somehow transplanted from planet to planet. This may happen should a planet, rich with life, be hit by a massive asteroid impact; pieces of that planet's crust will be propelled into space and any life contained within those samples may be transplanted to another world. If these hardy lifeforms make the trip, then perhaps they can gain a foothold and seed life in this new environment.
There are other hypothetical mechanisms by which life could “hop" from one planet to the next — including the fascinating possibility of “directed panspermia" where an intelligent civilization may deliberately seed other star systems with capsules containing its biological image. Other ideas remove the need for this life to survive the trip, allowing the freeze-dried dead biology attached to space rocks to act as a template for life on a newly seeded world, a process called “necropanspermia."
These processes are pure hypotheses right now, and this new research does not specify how life may spread, but we do know that chunks of planetary bodies can travel from planet to planet. For example, a type of meteorite found on Earth is known to originate from Mars — its isotopic signature is identical to measurements made by the armada of robots currently orbiting and roving on the Red Planet. These meteorites were bits of Mars crust blasted into space by ancient impacts.
It's not such a stretch to think that chunks of Earth have also been blasted into space and computer simulations suggest that there's a statistical chance that Earth rocks have drifted to the orbits of Jupiter and Saturn, potentially impacting some of the gas giants' moons. Whether or not Earth's abundant life was contained within these rocks is not known and it's quite a stretch to think that a secondary genesis of life may have been spawned.
But say if life can hitch a ride on space rocks and this life can seed new biospheres on other worlds… how would astrobiologists recognize that life is being spread from one star system to the next? Well, like a common cold, the spread would appear viral.
“Life could spread from host star to host star in a pattern similar to the outbreak of an epidemic. In a sense, the Milky Way galaxy would become infected with pockets of life," said co-author Avi Loeb, also of the CfA, in a press release.
Using a computer model, Lin and Loeb assumed that the “seeds" from one planet's biosphere spreads in all directions over time. Should one of those seeds reach a habitable planet, there's a chance it may take root. This creates several life-giving oases that could be detected by future space telescopes peering into these exoplanetary atmospheres. And should several of these life-endowed worlds be found, a pattern may emerge.
“In our theory clusters of life form, grow, and overlap like bubbles in a pot of boiling water," said Lin.
According to the authors, whose paper has been accepted for publication in The Astrophysical Journal Letters (and can be viewed on the arXiv preprint service), to see any kind of “viral" pattern, life would need to spread comparatively quickly, otherwise the motion of the stars around the galaxy will blur out the pattern. If a panspermia-like spread of life is occurring in the Milky Way, it would be ideal if Earth is located on the edge of a viral “bubble"; a situation whereby all the inhabited worlds are only found in one half of the sky, whereas the other half is devoid of life despite the presence of habitable exoplanets.
The fact that we may be able to decipher the biosignatures of life in the atmospheres of distant worlds is profound enough, but should we discover clusters of inhabited worlds, it begs the question: is panspermia a viable life-spreading mechanism? But even more than that, it questions the origin of life on Earth — did life originate here? Has it spread throughout the solar system or even to other stars?
Or was Earth just in the right place at the right time to catch the virus of life?
Source: CfA press release