>Not only is it closer to Earth and easier to visit than Enceladus, but evidence suggests its ocean may have existed for 4.5 billion years—longer than Earth’s oceans
Here's what I don't like. Nothing living appears on Europa's surface. In the same 4.5 billion years, Earth went from single-cell life to whales, jungles, and humans.
Radiation levels on Europa's surface are about 5 Sv in 24 hours, which is a massive dose; for reference, this is enough to kill 50% of humans exposed to it and make the survivors extremely ill.
It is also extremely cold (-171C mean) and near-vacuum (100 nanopascal).
If there is life in Europa and it bears any resemblance whatsoever to the biology we know, it simply couldn't exist on the surface. Even the hardiest single-celled organisms here, which have also had 4.5B years to evolve into uncontested niches, could barely survive a limited exposure to these factors.
80 mSv: 6-month stay on the International Space Station
1 Sv: Maximum allowed radiation exposure for NASA astronauts over their career
5 Sv: Calculated dose from the neutron and gamma ray flash, 1.2 km from ground zero of the Little Boy fission bomb, air burst at 600 m
5.1 Sv: Fatal acute dose to Harry Daghlian in 1945 criticality accident
He died 25 days later
54 Sv: Fatal acute dose to Boris Korchilov in 1961 after a reactor cooling system failed on the Soviet submarine K-19 which required work in the reactor with no shielding
Right, this is a possibility—but complex life doing so, in vacuum, at 100K? All I'm saying is, knowing what we know about chemistry, it seems extremely unlikely.
I'd be ecstatic to be proven wrong empirically, but it doesn't make sense to start our search there.
I mean, all of Europa is covered with a thick layer of ice and conditions above the ice layer are far from favorable for life. I'm not sure why you would expect to see anything on the surface?
Here's what I don't like. Nothing living appears on Europa's surface. In the same 4.5 billion years, Earth went from single-cell life to whales, jungles, and humans.