We shouldn't set foot on Mars for a long, long time. Read the bit about contamination.

https://idlewords.com/2023/1/why_not_mars.htm

> We can pretty much determine the composition of the atmosphere with spectroscopy

I don't believe (could be wrong, not an expert) that spectroscopy is sharp enough to tell you about the structure of complex molecules in Venus's upper atmosphere.

Please read the article.