Today, a study published by Universidad Nacional Autonoma de Mexico (UNAM) researchers reveals that Earth Brand™ Life might not have only rained down on neighboring planets, it may have the potential to spread further afield.
In a nutshell, one version of panspermia goes like this: when a sizable meteorite slams into a planetary body, pieces of the planet's crust may be blasted into space after being given the energy to attain "escape velocity" from that planet's gravity. The smaller the planet, the lower the escape velocity, so less energy is needed to blast bits of said planet into space. Therefore, as the logic goes, it's easier to eject bits of Mars than bits of Earth into space - as Earth is more massive than Mars and has a deeper gravitational well.
This is one of the reasons why it's thought there's fewer pieces of Earth floating around in space than pieces of Mars. Indeed, we know for a fact that bits of Mars have made the trip from Mars-to-Earth as we've found meteorites composed of Martian material here on Earth. Our robotic explorers have yet to find terrestrial meteorites on the Martian surface, but they do exist - just in smaller quantities.
So, with all this planetary material flinging around in the inner solar system, has some biology hitched a ride too? Well, that's open to debate and will remain a particularly controversial subject for some time to come.
But if Earth is a source of planetary ejecta (regardless of whether or not it's carrying microbes), how far has it traveled?
Well, Mauricio Reyes-Ruiz and his UNAM team have carried out the biggest Earth ejecta simulation ever and found a few surprising results.
Firstly, by analyzing 10,242 test particles (ejecta) originating from Earth, a far greater number of them end up on the Martian surface than previously estimated (an increase of two orders of magnitude). This finding will surely bolster the argument that Earth biology (dead or alive) may exist on the Martian surface.
Secondly, at higher ejection speeds (i.e. when the Earth is pummeled by bigger meteorites), the test particles had a higher likelihood of hitting distant Jupiter than landing on neighboring Mars.
As pointed out by the Technology Review‘s arXiv blog, this provides some tantalizing indications that Earth ejecta, potentially carrying microbes, has slammed into the surface of Jovian moon Europa - one of the handful of gas giant moons that have been singled out as having possible life-nurturing qualities. Europa is thought to harbor a sub-surface ocean, protected by a thick icy crust, with the potential to home complex marine life.
Although the researchers haven't specifically modeled Earth ejecta reaching Europa shores, just the fact pieces of Earth could reach the Jovian system is fascinating enough.
Conscious of the life-spreading potential of their simulated Earth ejecta, the Mexican researchers tracked the test particles for 30,000 (simulated) years to see where they ended up. 30,000 years is the period of time that scientists think the hardiest of Earth bacteria could survive in space in a state of dormancy. Sure enough, the test particles could, theoretically, reach Europa in that time frame.
Another, more far-reaching result of this research is that at higher ejecta velocities, the majority of the test particles are ejected from the solar system all together. Therefore, if there's some characteristic inside the small pieces of terrestrial ejecta that could preserve life for millions of years, this could hint at an Earth Brand™ Life transit method not only throughout the solar system, but to other stars.
But who said biology needed to be "alive" to make panspermia possible, anyway?
Image: Where it all begins - an impact event that kicks ejecta into space, carrying Earth biology. Credit: CORBIS