An idea off the forums could be poisionus without a environment suit, could have arsenic based lifeforms and ingredients and perhaps suit damage over time to
Since planets in our own solar system are incapable of supporting life as we know it (Venus having sulfuric acid in its atmosphere, if I'm not mistaken), and having other gasses like methane, it would only be realistic to have planets incapable of supporting human life. Personally I'd love to see planets like this.
