The more we can visit these planets (and the large moons in the solar system as well), the more we will look for any signs of life, current (unlikely in most cases, extremelyu unlikely that there is intelligent life) and past.
We don't know that we are the first (and as always, it will be impossible to proof that we are the first), but we have until now no serious evidence at all that there is or has been intelligent life in the solar system, and we have evidence that life as we know it would have had a hard time to develop at most of the planets and moons.
But for a while after we start to regularly visit planets, there will be countless searches for past life on those, and we will be much better able to give an answer then.

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Knowledge is a curse, but ignorance is worse