Billions more life-bearing planets the size of Earth may exist in the Milky Way, a study has claimed.
The research by an international team of scientists suggested a few hundred thousand billion of these dimly-lit icy planets, harbouring microbial life, could be floating in spaces between stars.
That equates to a few thousand for every star in the Milky Way.
The scientists believe the planets originated in the early Universe within a few million years of the Big Bang, and that they make up most of the so-called "missing mass" of galaxies.
According to their calculations, such planetary bodies would cross the inner solar system every 25 million years, and during each transit, zodiacal dust, including a component of the solar system's living cells, becomes implanted on the surface of these planets.
Since the first planet outside the solar system was discovered in 1995, the search for other so-called exoplanets has continued with some 750 now detected.
However, few have been deemed to have the potential to bear life.
The findings by the team, led by Professor Chandra Wickramsinghe, director of the Buckingham Centre for Astrobiology at the University of Buckingham, have been published online in the Springer journal, Astrophysics and Space Science.