The Milky Way Galaxy could be full of dead aliens killed by their own progress, scientists have claimed.
They say there is a strong chance most would have been "annihilated" by science and technology.
Researchers at NASA’s Jet Propulsion Laboratory, in California, say extraterrestrials might have emerged around eight billion years after the galaxy formed.
But the scientists also considered the "probability of self-annihilation for galactic complex life".
The team used an updated version of the equation to calculate how likely it is intelligent life exists, MailOnline reports.
They found there was a "high likelihood of intelligent life".
Researchers wrote: "Additionally, we found the potential self-annihilation to be highly influential in the quantity of galactic intelligent life.
"If intelligent life is likely to destroy themselves, it is not surprising that there is little or no intelligent life elsewhere."
Previous research has found "the progress of science and technology will inevitably lead to complete destruction and biological degeneration," they noted.
Scientists used the 1961 Drake Equation – which estimates the number of aliens in the Milky Way – to start with.
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They updated it using new information about the galaxy, such as the discovery of exoplanets, as well as the probability of self-annihilation.
The scientists warned if aliens do exist, they are "still too young" to be observed by us as well as being too far away from Earth to properly identify.
They estimated any existing intelligent life is around 13,000 light-years from the centre of the galaxy.
Earth and the solar system are an estimated 25,000 light-years away.
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In the study, published in arxiv, they wrote: "Therefore, our findings can imply that intelligent life may be common in the Galaxy but is still young.
"Our results also suggest that our location on Earth is not within the region where most intelligent life is settled."
Other experts have previously warned aliens might evolve differently to how humans do.
The NASA researchers said: "The timescale for biological evolution has been largely assumed to be identical to the intellectual species on Earth.
"Without considering the possibility that life may require varied timescales to evolve, any result of the growth propensity of life is dependent on the ongoing debate whether or not humans on Earth are the paradigm resembling all other evolving complex life."
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