Astronomers have long wondered whether life on Earth might have had origins somewhere else in the cosmos. The idea that the key ingredients for life, or even simple organisms, might be carried through space by non-animate objects—a concept known as panspermia—has been proposed as one way such “seeding” of life on Earth might have occurred.
But what if it could also happen in reverse? In other words, what if life were one day found on an alien moon, which could later be traced back to Earth?
This is the very idea presented in a new study that explores the provocative idea that Jupiter’s frozen moon Europa may not only be hospitable, but that life from Earth could be thriving there.
In the new study, published in the International Journal of Astrobiology, astrophysicist Zaza Osmanov of the Free University of Tbilisi explored whether Earthly bacteria might have been able to escape our planet by traveling on microscopic dust particles, which, after escaping Earth’s gravity, could have drifted through space until they reached Europa.
There, a vast subsurface ocean is believed to exist beneath the moon’s icy crust, meaning that any simple organisms capable of escaping from Earth on tiny spacefaring rafts of dust might have found their way to a new home, and one that could support life.
Panspermia, but in Reverse
The long-debated idea of panspermia already presents the general idea for how this might work. However, Osmanov’s study investigates this idea in reverse order: not only might life on Earth have originated from elsewhere, but our planet could also hypothetically be the source of similar “seeding” events that might occur on alien worlds.
Based on mathematical models, Osmanov calculated how bacteria-rich dust grains could be launched into space, resulting from collisions with incoming dust in Earth’s upper atmosphere. Upon escaping the planet’s gravity, some of these bacteria might be able to sail along toward distant locales like Europa with the help of pressure generated by solar radiation—essentially the same concept as a solar light sail spacecraft, albeit much smaller.
With the help of solar radiation and occasional gravitational interactions, Osmanov theorizes that some particles might eventually be “steered” by such natural processes over time, eventually making their way to Jupiter.
Tiny Earthling Alien Invaders
Based on Osmanov’s estimates, there could potentially be as many as hundreds of millions of Earth-originating dust particles that might make their way to Europa every second. That’s a significant number, and although he estimates that the majority would be destroyed on impact, a small fraction could arrive at extremely shallow angles, which he believes may be able to survive landing on Europa’s surface.
However, even if a few bacterial invaders managed to survive, the next challenge they would face would be to reach the moon’s ocean that astronomers believe to be concealed beneath its icy exterior. Based on past studies, tidal forces generated by the massive host planet Jupiter offer a solution: such events are believed to likely cause fractures in Europa’s icy shell, which lead to the creation of entry points where surface materials might be capable of migrating downward.
Adding to this, Osmanov also points to instances where ice melting may also provide a means for the movement of material from the surface down into the moon’s hidden ocean. Over periods of thousands of years, some of these tiny bacterial invaders might make their way past the harsh surface environment and down into the moon’s far more hospitable subsurface ocean.
Osmanov estimates that there may be considerable numbers of Earth-derived particles that could reach Europa’s ocean over geological timescales. This could mean that terrestrial particles, Earthly microbes that have made the journey, may have had time to establish themselves as microbial colonists—if, of course, current presumptions about the moon’s conditions for supporting life are correct.
While the theory remains speculative, and Osmanov concedes that it cannot be tested directly at present, it suggests something fascinating: that the eventual discovery of life on an alien world could have ancestral links to our own planetary home.
Osmanov’s recent study, “Earth as a potential source of life for Europa’s subsurface ocean,” appeared in the journal International Journal of Astrobiology.
Micah Hanks is the Editor-in-Chief and Co-Founder of The Debrief. A longtime reporter on science, defense, and technology with a focus on space and astronomy, he can be reached at micah@thedebrief.org. Follow him on X @MicahHanks, and at micahhanks.com.