EARTH may be one of the first habitable planets in the universe, a new study suggests.
Scientists believe when the solar system came into being 4.6 billion years ago, only 8% of the potentially life-supporting worlds that are destined to exist had formed.
The vast majority are yet to be born and many will not appear until after the sun burns itself out in another six billion years.
Astronomers came to the conclusion after analysing data from the Hubble and Kepler space telescopes.
Lead researcher Dr Peter Behroozi, from the Space Telescope Science Institute (STScI) in Baltimore, US, said: “Our main motivation was understanding the Earth’s place in the context of the rest of the universe. Compared to all the planets that will ever form in the universe, the Earth is actually quite early.”
Galaxy observations show that 10 billion years ago stars were forming rapidly, but the process used only a fraction of all the hydrogen and helium in the universe.
Today, stars are being born at a much slower rate and, with the amount of raw material still available are likely to continue being created for a very long time to come.
Kepler had shown that Earth-sized planets occupying “habitable zones” - the orbital path just the right distance from a star to allow liquid surface water - are common in our galaxy, the Milky Way, the scientists added.
They estimate there could be one billion Earth-sized worlds in the Milky Way, a large proportion of which are rocky.
That figure soars when the other 100 billion galaxies in the observable universe are taken into account.
The last star is not expected to snuff out until 100 trillion years from now, providing time for untold numbers of potentially life-sustaining Earth-like planets to form in habitable zones.
Future Earths are more likely to appear inside giant galaxy clusters and dwarf galaxies which still have large reserves of star-building gas, said the scientists.
One advantage of coming early to the party is that powerful telescopes like Hubble can be used to trace the development of galaxies back to the Big Bang that created the universe.
Because of the run-away expansion of the universe, such observable evidence will be virtually erased one trillion years from now.
Any civilisation arising in the far-future will be left with no clue - from astronomy at least - to how the universe began and evolved.
The research is published in the journal Monthly Notices of the Royal Astronomical Society.