Maybe, but slowing down enough to land is the problem.
To convert from a flyby to landing, you need to burn a lot of fuel, to slow down. To get that fuel to the destination, you need to bring it with you. Which means a much higher take off mass, which needs an even bigger rocket.
Mars has a very light atmosphere, which lets us aerobrake- slow down by hitting the atmosphere, that way you don't need any extra fuel. Europa's atmosphere is basically non-existent.
> Would we not learn a lot more by landing on these moons?
Probably, but it's also a lot harder. Not only does it require more delta-V, you now need to design, build and test a lander in addition to a spacecraft, and you need to build everything to be able to operate in Jupiter's harsh radiation environment (Europa Clipper will only do fly-bys of Europa and spend most of its orbit further away from the high radiation environment).
There are so many science fiction stories about exploring and colonizing Jovian moons. But somehow the authors always gloss over the radiation issue. Unshielded humans would probably be dead in a matter of days.
AFAIK Jovian radiation is very strong and our current machines have hard time surviving in proximity of the planet for any significant time. Even Clipper will stay a healthy distance away most of the time and only visit the inner Jovian system shortly.
We might, and we are (just not Jupiter's moons)! The Dragonfly mission (https://dragonfly.jhuapl.edu), will launch in 2027 and arrive at Saturn's moon Titan in 2036.
Dragonfly is a nuclear powered octo-copter, that will fly autonomously on the moon. Titan's small gravitational field and dense atmosphere (about 1.45x Earth's atmospheric pressure) make it one of the best places in the Solar System for flight. The general flight plan is to charge up batteries with the MMRTG (https://en.wikipedia.org/wiki/Multi-mission_radioisotope_the...), take off, scout a new potential landing area, land in a previously scouted landing area. On one battery charge, it will be able to fly up to 10km, and stay aloft for up to 30 minutes. Dragonfly will carry out scientific sampling both on the ground and in the air.
> Titan is similar to the very early Earth, and can provide clues to how life may have arisen on Earth. In 2005, the European Space Agency's Huygens lander acquired some atmospheric and surface measurements on Titan, detecting tholins,[29] which are a mix of various types of hydrocarbons (organic compounds) in the atmosphere and on the surface.[30][31] Because Titan's atmosphere obscures the surface at many wavelengths, the specific compositions of solid hydrocarbon materials on Titan's surface remain essentially unknown.[32] Measuring the compositions of materials in different geologic settings will reveal how far prebiotic chemistry has progressed in environments that provide known key ingredients for life, such as pyrimidines (bases used to encode information in DNA) and amino acids, the building blocks of proteins.[33]
> Areas of particular interest are sites where extraterrestrial liquid water in impact melt or potential cryovolcanic flows may have interacted with the abundant organic compounds. Dragonfly will provide the capability to explore diverse locations to characterize the habitability of Titan's environment, investigate how far prebiotic chemistry has progressed, and search for biosignatures indicative of life based on water as solvent and even hypothetical types of biochemistry.[6]
> The atmosphere contains plentiful nitrogen and methane, and strong evidence indicates that liquid methane exists on the surface. Evidence also indicates the presence of liquid water and ammonia under the surface, which may be delivered to the surface by cryovolcanic activity.
My understanding about planetary protection is that you don't want to contaminate the new environment, because then you can't say for certain (that easily) if the life you are detecting is native to the environment or the contamination.
I also understand that the native population of the Americas suffered badly from the diseases carried in by the europeans. But those diseases landed in an environment much like the one they evolved in. The humans were humans, the atmosphere were the same, the temperature were the same, etc.
If the space-probe gets contaminated with some earthly bacteria, virus or prion they not only have to survive the travel there, but then they have to quickly adapt to the new environment. Different temperature, different chemical composition, different life forms. How often does it happen that you sneeze at a fungi and the fungi gets infected with your cold? Doing one of these adaptation alone is a big ask, doing all of them at once would be a huge leap.
Imagine that you move to a new place. You move there in a salted barrel, not designed for human occupancy. The locals speak a different language, have different customs, you can't get food you are used to and the climate is way out of your comfort zone. Would you be outcompeting the locals quick? I don't think so.
I wouldn't worry about wiping out a whole ecosystem unless the ecosystem is much much more similar to our own's.
But of course being cautious is always a good idea. Furthermore I already think we should avoid contamination. If for no other reasons than to avoid arguments about what the detected life really means.
Would we not learn a lot more by landing on these moons?