Ehm, lets be pragmatic.

You need a life sciences specialist to keep the life support system and food cultivation (which will likely serve some combination of both functions) running.

A full on, dedicated medical specialist. ZERO other responsibilities other than monitoring crew health, which will include some interesting research possibilities of its own.

A nuts and bolts mechanic. Someone who's purpose in life is the physical machinery they use. Ideally, this person is also a pilot.

A mission commander with some kind of general science background capable of operating the necessary information gathering equipment.

And finally, a planetary sciences specialist, with a fairly broad background in environmental studies and ecology.

Notice a serious lack of research brainpower? Good, you've been paying attention. Let the eggheads back on Earth interpret the pigeon entrails, keep the people on the ground out of the esoteric and focused on getting the job done safely in a fairly hostile environment.

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I'm not completely heartless, the doctor who removed it told me he'd never be able to get it all.