Seeding Life on the Moons of the Outer Planets via Lithopanspermia from 1 billion life bearing meteroids from Earth and Mars

Material from the surface of a planet (like Earth or Mars) can be ejected into space by a large impact and could carry primitive life-forms with it. Researchers performed n-body simulations of such ejecta to determine where in the Solar System rock from Earth and Mars may end up. They found that, in addition to frequent transfer of material among the terrestrial planets, transfer of material from Earth and Mars to the moons of Jupiter and Saturn is also possible, but rare. They expect that such transfers were most likely to occur during the Late Heavy Bombardment or during the ensuing 1–2 billion years. At this time, the icy moons were warmer and likely had little or no ice shell to prevent meteorites from reaching their liquid interiors. They also note significant rates of re-impact in the first million years after ejection. This could re-seed life on a planet after partial or complete sterilization by a large impact, which would aid the survival of early life during the Late Heavy Bombardment.

The researchers calculated that over the course of 3.5 billion years — roughly the amount of time Earth is known to have possessed life — about 200 million meteoroids large enough to potentially shield life from the rigors of space were blasted off Earth. They also estimated roughly 800 million such rocks were ejected off Mars during the same period. More rocks escape from Mars because Martian gravity is a little more than a third that of Earth’s.

Past research suggested moderately-sized rocks ejected from impacts could protect organisms from the dangers of outer space for up to 10 million years. The scientist calculated about 83,000 meteoroids from Earth and 320,000 from Mars could have struck Jupiter after traveling 10 million years or less. Also, roughly 14,000 from Earth should have hit Saturn in that time, and no more than 20,000 from Mars.

4 great moons of Jupiter: Io, Europa, Ganymede and Callisto. Image Credit: NASA/JPLM

The idea that life can spread through space is known as panspermia. One class of panspermia is lithopanspermia — the notion that life might travel on rocks knocked off a world’s surface. If these meteoroids encase hardy enough organisms, they could seed life on another planet or moon.

Although lithopanspermia might seem farfetched, a number of meteorite discoveries suggest it might at least be possible. For instance, more than 100 meteorites originating from Mars have been discovered on Earth, blasted off the red planet by meteor strikes and eventually crashing here.

Some researchers have even suggested that life on Earth may have originally been seeded by meteors from Mars. A great deal of research has explored whether the red planet once harbored life and whether life might still exist there today, based on findings that Mars might once have been significantly more hospitable to life than it is now, and that refuges for life could remain hidden under its surface. One Martian meteorite, Allan Hills 84001 (ALH84001), was even initially claimed to contain evidence of life. However, research since has revealed that every item on this meteorite that was potentially suggestive of life could be generated inorganically.

The researchers note the icy moons of Jupiter and Saturn were all once warmer and likely had little to no icy shell to prevent meteorites from reaching their liquid interiors as they do now. In addition, Europa currently has the thinnest ice crust of the six moons the researchers examined, and roughly 40 percent of its crust appears to be covered with “chaos regions,” uneven terrain hinting that it often breaks into large chunks separated by liquid water that later refreezes. Any meteorites on top of such regions therefore might have a chance of falling down into the underground oceans that moon is suspected to have.

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