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.