Meteoroid transfer of Earth life to Europa? Options

[Guest_BruceMoomaw_*]

As promised, here are my conclusions after reading Mark Peplow's new report on Brett Gladman's paper to the LPSC meeting ( http://www.nature.com/news/2006/060313/full/060313-18.html ). I really don't see anything at all in it that wasn't in the earlier LPSC abstract of Gladman ( http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2165.pdf ) -- except that Peplow quotes Gladman as saying that (1) for every 600 million meteorites flung away from Earth by impacts, "about 100 objects would hit Europa", while Gladman's abstract actually says there would be "30-100"; and (2) outnof that many Earth meteorites, Peplow says "roughly 30" would hit Titan, while Gladman's actual abstract says "a few to 20" (and provides a graph).

This doesn't make any difference to the overall results -- based on numbers alone, it is (contrary to my previous fond wish) quite possible that Earth could have inoculated Europa with terrestrial life, so that the discovery of Europan life would NOT automatically prove that life had evolved in two separate world within the same solar system and that life must therefore be common in the Universe. However, both reports point out that those Earth meteorites would hit Europa at 20-30 km/sec, and that therefore (to quote Peplow) such crashes "would almost certainly sterilize the few rocks that made it that far." Peplow calls this "unfortunate" -- which is the exact opposite of my feeling about it; that impact speed really may allow us to consider Europa as a separate laboratory to look for the evolution of life, totally free of Earth biocontamination.

As for Titan, its atmosphere would slow any arriving Earth meteoroids down to such low speeds that they might very well biocontaminate that world -- IF the bacteria in the meteoroids could survive Titan's cryogenic near-surface temperatures. Note also that the problem of high impact speed onto Europa does NOT rule out the possibility that life might have originally evolved only on Europa, and then been transferred from there to Earth and/or Mars early in the Solar System's history!