[adekok]

> If life is there, completely disconnected from earth life,

IIRC (I can't find the reference now), the "dinosaur killer" asteroid would put rocks from Earth into space. With sufficient velocity that they could reach nearby solar systems within 100M years.

So from a strictly physical point of view, I would argue that the odds of Earth "infecting" Europa with life in the past 3 billion years are pretty much 100%.

[scoofy]

>So from a strictly physical point of view, I would argue that the odds of Earth "infecting" Europa with life in the past 3 billion years are pretty much 100%.

This is exactly why europa is so important. It's that the gravity well of jupiter is so great, that infection of europa is extremely unlikely, rather than being extremely likely. Europa would be a vastly better case for arguing separate origins of life than any other place in our solar system.

Since earth has only existed for a short time in the grand scheme of things, and supposing that life indeed sprung here on its own, the odds of a random rock from a random few impacts landed on europa, rather than jupiter, in such a way to get to survive is absurdly small.

[hackuser]

Europa is an extremely tiny target to hit randomly from Earth, probably made smaller by the fact that, in order to hit Europa, the object has to pass near Jupiter without getting pulled into it.

On the other hand, there are billions of years of random attempts, as you said.

[adrianN]

But there is a big lump of mass near Europa that tends to attract projectiles.

[hackuser]

Yeah, that's why I said "probably". I wonder if it's a net gain or loss in the game of 'drop a rock on Europa'. At this point, I'm leaning toward 'gain'.

[kerbalspacepro]

You mean the wormhole with a blackhole on the other side?

[Symmetry]

Europa doesn't have an atmosphere and it's laying at the bottom of a pretty steep gravity well, over 10 km/s from Jupiter intercept to the surface. Earth to Mars or vice versa microbial transport is pretty credible and you might even have a dormant cell from elsewhere falling down to Europa in a meteor. But I'm not sure I'd swallow any cell surviving Europa lithobraking.