There's a major problem sterilizing the robot enough for this mission. Because we don't want to introduce any Earth life to the Europa ocean. In principle, heat it enough, or using enough ionizing radiation you can sterilize it. And if you can remove all the organics from the lander, then it should be sterile. But in practice all the ways we know of doing that also destroy electronics and other delicate spacecraft components - or else are not 100% effective.

There are several techniques being explored. But we don't yet have 100% sterilization. That's especially tough if your lander is going to end up in an ocean that may perhaps have vulnerable lifeforms, e.g. life that is simpler than DNA life and that was out evolved on Earth, to take an example.

On the plus side, we might not have to drill down all the way. Enceladus has geysers that seem to come from permanent cracks 1 meter wide on average all the way down to its subsurface ocean. It's actually ejecting its ocean into space, slowly. and they find salt in the spray of ice from its geysers. So that at least is a place where you don't need to drill, can just sample the plumes themselves.

Europa hasn't been studied close up to the same extent that Enceladus has been, and also has higher gravity so its geysers would be lower probably. But it has things that make it promising.

First, it has signs of chaotic terrain on the surface that may be due to plumes of water rising from the ocean, a bit like lava plumes on Earth. As they break through to the surface they turn into icebergs which turn over, in this model. If so - well one of them is a dip still, not a rise. Which suggests that there may be liquid water (denser than ice) below it. If so there may be a liquid plume close to the surface of Europa.

It would be a great place to visit, maybe even might have plumes also? But we need to study Europa more closely first.

NASA has been mandated by the US government to include a lander on its Europa mission. But I think that's the wrong way round to do things myself, for politicians to make such a decision. Because - until we have close up images, we can't design the lander anyway. For instance Europa may be covered in thin blades of ice, which would make it really hazardous to land. It might have geysers, in which case you don't need to land at all, and can sample the water from orbit. It might have liquid water on the surface in which case you could only land if your lander is very thoroughly sterilized and may be that the spaceship gets there only to find out that it can't land its lander in the most promising landing site for planetary protection reasons.

And - if you send an orbiter first to look at it close up, then - by the time we get the data back, some time in late 2020s or 2030s, then surely rocket technology has moved on a lot. We may be able to design a lander and send it in a follow up mission very quickly. I don't think it's the right decision to delay the launch now, in order to design and add an all purpose lander to land on any concievable site on Europa, with no clear idea of what exactly it would be studying.

I think the politicians who drafted that proposal perhaps didn't realize quite how little we know about Europa - we haven't had a good close up study at all, lots of flyby images but only a few of them are high resolution.

Also I think you should never say that we "have to land" somewhere - as whether you can or not depends on planetary protection considerations. If you can't do it consistent with planetary protection - then the whole mission might get called off. It has to be a suggestion "it would be really good if we can land on Europa" and leave it to the scientists to then research into whether that is possible technically, cost effective, and also possible within the demands of planetary protection. You need a possibility of dialogue back and forth as the project continues. And as it is, then NASA also may be forced to launch using the SLS which doesn't exist yet due to the extra mass of the lander.

It's great that they prioritized Europa though.