Has Earth spread life in the Solar System ?
Earthly bacteria could have reached distant planets and moons after being flung into space by massive meteorite impacts, scientists suggest. The proposal neatly reverses the panspermia theory, which suggests that life on Earth was seeded by microbes on comets or meteorites from elsewhere. Both theories envision life spreading through the Solar System in much the same way that germs race around a crowded classroom, says Jeff Moore, a planetary scientist at NASA's Ames Research Center in Moffett Field, California. "Once one planet comes down with life, they all get it."Impacts on Mars and the Moon are known to throw rocks into space that end up on Earth as small meteorites. But spraying Earth rocks towards the edges of the Solar System is more difficult, because the material has to move away from the Sun's strong gravity.To find out just how many rocks could reach the outer Solar System, a team of scientists used a computer model to track millions of fragments ejected by a simulated massive impact, such as the one that created the Chicxulub crater some 65 million years ago.
Similar sized events are thought to have happened a few times in Earth's history.The researchers looked in part at how many Earthly fragments would reach environments thought to be relatively well suited to life, such as Saturn's moon Titan and Jupiter's moon Europa. "I assumed the answer would be very, very few," says Brett Gladman, a planetary scientist at the University of British Columbia, Vancouver, Canada, who led the team. But Gladman was surprised to find that within 5 million years, about 100 objects would hit Europa, while Titan gets roughly 30 hits. He presented the results at the Lunar and Planetary Science Conference in League City, Texas, on 16 March.
Earthly bacteria could have reached distant planets and moons after being flung into space by massive meteorite impacts, scientists suggest. The proposal neatly reverses the panspermia theory, which suggests that life on Earth was seeded by microbes on comets or meteorites from elsewhere. Both theories envision life spreading through the Solar System in much the same way that germs race around a crowded classroom, says Jeff Moore, a planetary scientist at NASA's Ames Research Center in Moffett Field, California. "Once one planet comes down with life, they all get it."Impacts on Mars and the Moon are known to throw rocks into space that end up on Earth as small meteorites. But spraying Earth rocks towards the edges of the Solar System is more difficult, because the material has to move away from the Sun's strong gravity.To find out just how many rocks could reach the outer Solar System, a team of scientists used a computer model to track millions of fragments ejected by a simulated massive impact, such as the one that created the Chicxulub crater some 65 million years ago.
Similar sized events are thought to have happened a few times in Earth's history.The researchers looked in part at how many Earthly fragments would reach environments thought to be relatively well suited to life, such as Saturn's moon Titan and Jupiter's moon Europa. "I assumed the answer would be very, very few," says Brett Gladman, a planetary scientist at the University of British Columbia, Vancouver, Canada, who led the team. But Gladman was surprised to find that within 5 million years, about 100 objects would hit Europa, while Titan gets roughly 30 hits. He presented the results at the Lunar and Planetary Science Conference in League City, Texas, on 16 March.
