News in Science

Impacts may spread life to other planets

Interplanetary colonists New computer simulations indicate microbes inside rocks blasted from Earth could survive long enough to reach other places in the solar system.

The study reported in the pre-press physics blog arXiv.org, and submitted for publication in the journal Icarus, is a new twist on the panspermia hypothesis that suggests the seeds for life on Earth come from outer space.

Scientists including Mauricio Reyes-Ruiz from the Universidad Nacional Autonoma de Mexico used computer modelling to show how an asteroid or comet slamming into Earth with enough velocity would kick impact ejecta up into space.

Reyes-Ruiz and colleagues found depending on the velocity and impact location, debris would reach the orbits of the Moon, Venus, Mars, Jupiter and beyond.

They placed a 30,000-year time limit on their computer model to take into account the damage done by radiation and cosmic rays on any bacteria surviving in the ejecta.

Reyes-Ruiz and colleagues found depending on impact location and velocity, about 5 per cent of ejecta thrown into space would fall back to Earth.

But more interestingly, their models found up to 0.02 per cent would reach the Moon, 0.17 per cent would reach Venus, 0.01 per cent would reach Mars, 0.06 per cent would reach Jupiter, 0.19 per cent would fall into the Sun and a staggering 6.75 per cent would reach the orbit of Pluto.

Better computing power

Planetary Scientist Dr Simon O'Toole from the Australian Astronomical Observatory says the work has only been made possible thanks to advances in computing power.

"In the past we didn't have the processing capacity to carry out these simulations beyond the Moon or Venus," says O'Toole.

"Now thanks to more powerful computers we can produce more detailed models which include the rest of the solar system."

O'Toole says, "The new models have come up with some interesting findings".

"If the impact happens on the side of Earth facing the planet's orbital direction, ejecta could reach Mars and Jupiter, while an impact on Earth's trailing side could only reach the Moon or Venus."

DNA in space

Associate Professor Dr Charley Lineweaver from the Australian National University Mount Stromlo Observatory says any findings depend on how long bacteria could survive in space.

"We don't even know how long bacterial spores remain viable inside ice," says Lineweaver.

"Bacterial survival in space is an active field of research but the simple answer is we don't know how long microbes could survive given the harsh space environment."

"It depends where the bacteria is. If it's on the surface it's got less chance of survival than if it's protected by one, two or three centimetres of rock."

Lineweaver says, "It's an interesting study because we can reverse the problem and suppose the ejecta originated on Mars and came to the Earth".

"We would love to know if we're Martians."