An international team of scientists led by Professor Chandra Wickramasinghe, of the University of Buckingham, published their finding in the journal Astrophysics and Space Science.
Recent estimates have suggested that our galaxy has as many planets as stars -- approximately 200 billion - with most of those planets not orbiting a star. But this latest study dramatically increases the number of 'free-floating' planets.
Wickramasinghe and colleagues propose that these planets originated in the early universe a few million years after the Big Bang, and that they make up most of the so-called "missing mass" of galaxies, known as dark matter.
They calculate that on average our solar system would be visited by a free-floating planet once every 26 million years. As each one passes by our solar system, it accumulates up to 1000 tonnes of interplanetary dust onto its surface.
"If the dust included microbial material that originated on Earth ... this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy," they write.
Dr Simon O'Toole, an astronomer at the Australian Astronomical Observatory, isn't convinced the number of free-floating planets is so high.
"It's a fascinating idea, but involves too many assumptions to say for sure that it's going to be real," says O'Toole.
Read more at Discovery News
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