Life may have spread among the stars like an infectious virus, leaving a distinctive pattern that we can recognise, say scientists.
There are two ways this can happen – through organic “seeds” of life being transported by asteroids or comets, or via an advanced space-faring race visiting new worlds.
The researchers did not study the likelihood of the second sci-fi scenario, only the feasibility of spotting such a “panspermia” of life.
“In our theory clusters of life form, grow, and overlap like bubbles in a pot of boiling water,” said lead scientist Dr Henry Lin, from the Harvard-Smithsonian Center for Astrophysics (CfA) in the US.
The model assumes that life emerging on one living planet spreads outward in all directions. If a “seed” – be it a cocktail of organic molecules or a band of alien colonists – reaches a habitable planet orbiting a nearby star, life can take root.
Over time, the result of this process would be a series of life-bearing oases dotting the landscape of our galaxy, the Milky Way.
Co-author Dr Avi Loeb, also from the CfA, said: “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.”
Such an epidemic-like pattern should be possible to identify from Earth. For example, if the Earth happened to be on the edge of a “bubble” of life, all the nearby life-hosting worlds would be in one half of the sky.
But a panspermia pattern would only show up if life spread sufficiently rapidly, say the scientists. Since stars move relative to one another, close neighbours are likely to drift apart over time scales of millions of years.
Stellar drift would have the effect of smearing out the life cluster “bubbles”.
The research is due to appear in the Astrophysical Journal Letters.