if I'm correct you can find plants growing in the present and no dead plants, so the future portal is actually venus.
English
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The future portal is the red world. Green world enemies are called Precursor Vex, meaning before. The red world has two portals, but one is broken, meaning it used to exist in the past, hence red world is in the future.
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But think about it in this perspective. Live existed before and after there is only ruins. Plus another poster said that the gates are both Venus not two planets which would make perfect sense as past and future reference. If they're both 2 different planets then the past and future analogy wouldn't make sense at all.