@rockwizard :
Unfortunately, @chasebf has got it right mostly, especially their first response in this thread. I do think that the human mind is very complex and no tests could adequately judge its abilities. Having said that, adcom will definitely want to base their decision on something more concrete, e.g., your GRE score. Now, great thing about the US is this: it is super rich and can entertain all sorts of possibilities. Meaning, there are professors who will dismiss GRE right away. But, there are others who will NOT budge a tad bit if you could not pass their threshold.
Personally, I am suffering from my bad GRE quant score (155). Usually, I take more time thinking about even the simplest things. I do think it is a strength because it allows me to get a deeper understanding of any concept or topic. However, anyone can disagree and refuse me to offer an opportunity based on just that. It is what it is.
Apart from all that, you truly need to think really hard about a career in planetary science. Given the funding situation, it is like hunger games. Even a Caltech Ph.D. can't necessarily save you from the real world. My two cents.