The Supreme Court, Martians, Justice Jackson, and Chief Justice Roberts
Justice Jackson's dissent in the universal injunction case (CASA, Inc. v. Trump) includes this line:
A Martian arriving here from another planet would see these circumstances and surely wonder: "what good is the Constitution, then?" What, really, is this system for protecting people's rights if it amounts to this—placing the onus on the victims to invoke the law's protection, and rendering the very institution that has the singular function of ensuring compliance with the Constitution powerless to prevent the Government from violating it? "Those things Americans call constitutional rights seem hardly worth the paper they are written on!"
Some people have suggested there's something strange or inappropriate about bringing Martians into it, but it seems a pretty familiar locution. Here, for instance, is Chief Justice Roberts from Riley v. California (2014), which labels it familiar enough to be "proverbial":
These cases require us to decide how the search incident to arrest doctrine applies to modern cell phones, which are now such a pervasive and insistent part of daily life that the proverbial visitor from Mars might conclude they were an important feature of human anatomy.
Justice Thomas used a similar phrase in Foster v. Chatman (2016) and Justice O'Connor in Engle v. Isaac (1982), both quoting Judge Henry Friendly, Is Innocence Irrelevant? Collateral Attack on Criminal Judgments, 38 U. Chi. L. Rev. 142, 145 (1970):
The proverbial man from Mars would surely think we must consider our system of criminal justice terribly bad if we are willing to tolerate such efforts at undoing judgments of conviction.
The "proverbial man from Mars" refers to someone who looks at things afresh, without focusing on the social conventions or legal frameworks that (the speaker suggests) might blind us to what's actually going on. You can agree or disagree with Justice Jackson's substantive argument about universal injunctions, but judges and Justices have been using the Martian thought experiment for generations.
(The pedant in me does agree, though, that "Martian arriving here from another planet" is redundant, in a way that "proverbial visitor from Mars" is not. But that really is pedantry.)