A space explorer leads an expedition after believing to have discovered paradise which gradually descends into madness.

The goal is obvious enough to me (although the wording may need a polish): ?he's Moses-in-outer-space leading his crew to ?a better world, to an alluring paradise.

But is it the real deal, or only a mirage? ?Is the descent into madness the result of pursuing a delusion?

I sense some interesting raw ore for a psycho-drama, but I think the concept needs refining.

Is finding paradise the inciting incident? If so what is the causal connection to his goal? And as Richiev asked, what is his goal?

You have not given us a goal for the lead character, that is an important missing piece of your logline.
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"As he explores an idyllic planet which ?could serve as the new home for humanity, an intrepid explore must fight his way back to his spaceship when the supposed Paradise turns deadly."