Some writers overuse quotation marks, perhaps (among other, less identifiable reasons) thinking such marks should be used every time any common expression or turn of phrase comes up. The thing is, those quotation marks indicate so-called, which means the thing isn’t really what it’s being called. (Note: If you actually write so-called before the expression, do not use quotation marks around the expression itself.) Some people on the internet call these sarcasm quotes, scare quotes, etc.
Get rid of those quotation marks, and this sentence is good.
Humans return from Mars for the first time, but there is something not quite right about them.
(Yay! A compound sentence with a comma in the correct place!)