Perhaps microbes are riding on specks of dust.
A grain less than a tenth of a millimetre across would still be capable of carrying microscopic life, says Napier. And the pressure of sunlight can quickly blow grains this small out of the solar system. The same force might one day propel spacecraft through the cosmos.
Such a grain could travel about six light years from Earth in 70,000 years – far enough to reach other stars. We could be surrounded by a huge ‘biodisk’ of frozen organisms floating on grains of rock, says Napier, all of which can wander in and out of our solar system quite easily. “The solar system is as leaky as a sieve,” he says.
Earth should spread its seed widest when we pass through a giant molecular cloud, a mass of dusty material from which stars are born. This has happened about five times since life appeared on Earth.
Each time, Napier estimates about three billion trillion microbes passed from Earth into the cloud. The chances of some of these finding their way to an Earth-like planet are quite high, he says. A similar process could even explain how the Earth wound up hosting life in the first place, he adds.
Panspermia is one of my favorite words.