MICROBES from Earth could have journeyed to Saturn’s moon Titan and may even be thriving there. This startling suggestion comes from a massive computer simulation of what could happen to Earth rocks blasted into space by a large meteor impact.
An impact of the type that caused the mass extinction of species at the Cretaceous-Tertiary boundary could eject more than half a billion rocks from Earth into space. Our planet has had quite a few impacts of at least this magnitude in its four-billion-year history, says Brett Gladman of the University of British Columbia in Vancouver, Canada. “We know that meteorites can escape the gravity well of large planets,” he says, pointing to the meteorites from Mars that have been found on Earth.
Gladman’s simulation looked at where such rocks might go after they left Earth. Earlier models had examined the probability of Earth rocks reaching Mars, but he wanted to see whether they might travel further out towards potential habitats for life, such as Jupiter’s moon Europa and Saturn’s moon Enceladus, each thought to contain frozen-over seas of liquid water, or Saturn’s giant moon Titan, which has an atmosphere thicker than Earth’s and is rich in organic molecules.
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The simulations showed that each Earth impact would propel about 100 rocks to the surface of each of the large moons of Jupiter. However, although microbes living in these rocks could survive the force of being blasted off Earth, and even the thousands of years travelling through space, the arrival on the moons could kill them. “The impact speeds are incredibly high,” Gladman says – up to 25 kilometres per second. The same fate would also await any bug that made it to Enceladus.
Titan is a different story, however, thanks to its thick atmosphere. The simulation showed that about 30 rocks from a large impact on Earth would make it to Titan, where they would likely shatter in the moon’s upper atmosphere, and the fragments would land relatively gently on Titan’s surface. Whether organisms that evolved on a warm Earth would be able to survive on icy Titan is another story, but it is at least conceivable, says Gladman.
“Rocks from a meteor impact on Earth making it to Titan would land relatively gently, thanks to the thick atmosphere”
“The results are quite compelling,” says Jay Melosh of the University of Arizona in Tucson. But he is “rather sceptical that the microbes would find a hospitable environment” on Titan.
