ALIEN species may be meteor-hopping across space and quietly colonising the galaxy, a fringe theory suggests.
It's a concept known as panspermia, and it resembles how plant species can migrate when their seeds are spread by birds.
The hunt for alien life is difficult - especially when scientists aren't entirely sure what they're looking for.
But a pair of astronomers, Harrison B. Smith and Lana Sinapayen, have decided to focus less on what life would look like and more on what life would do to survive.
If life is less viable on one exoplanet, alien life that is capable of panspermia will try elsewhere.
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And that can be done by hitching a ride on meteorites or other celestial bodies, the pair write in a new study, that is awaiting peer review.
If the conditions are right, life might thrive.
With new life, the new planet would begin to resemble the alien lifeforms 'home' planet - like how Earth changed in accustom to humans.
Smith and Sinapayen aim to identify potential biosignatures scientists can use to spot life on other planets from afar.
For example, there is far more oxygen in Earth's atmosphere today than there would be if life was not present.
This is what makes our water world look so green to distant observers.
Extraterrestrial species that are capable of panspermia would attempt to make those same changes on every planet they came across.
Cosmic chaos
Our universe is incredibly chaotic.
And while the galaxy we call home is currently quite peaceful, it has endured a violent past long before human beings came to be.
Martian meteorites have been found on Earth, dating back to these formative years.
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Scientists are confident in life's ability to 'find a way'.
An attempt at life on one exoplanet might fail, but might succeed on the next - it's all about finding those 'goldilocks' conditions for survival.
But the theory suggests that life doesn't have to begin on it's 'home' planet.
Instead, life could have blossomed on exoplanet number one, two, three or 4,000.
It's an interesting concept, particularly when looking at our own existence on this blue rock of ours.
