Dr Simon O'Toole, an astronomer at the Australian Astronomical Observatory, isn't convinced the number of free-floating planets is so high. this process offers a way by which evolved genes from Earth life could become dispersed through the galaxy," they write. 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. "It's a fascinating idea, but involves too many assumptions to say for sure that it's going to be real," says O'Toole As each one passes by our solar system, it accumulates up to 1000 tonnes of interplanetary dust onto its surface. They calculate that on average our solar system would be visited by a free-floating planet once every 26 million years. "If the dust included microbial material that originated on Earth...
He also questions the rate at which such planets would encounter our solar system.
"Any planet that came near our solar system would cause all sorts of gravitational disturbances among the planets," says O'Toole. "[Therefore any encounters] would only be around the very edges, beyond Neptune's orbit."
Despite some scepticism in astronomical circles, he says it is possible for free-floating planets to collect material from our solar system.
"I like the idea of these wandering planets picking up microbial matter, a kind of panspermia idea. People are very interested in it, but aren't 100 per cent behind it."