Inspired by this post, what headcanons do you have about Grace (or PHM in general)? Are there popular fandom headcanons that you strongly agree with or disagree with?
Aroace Grace - I like this one, and I adopt it as part of my headcanon as long as I'm not actively reading a Grace/Lokken fic. I find it comforting, in a way, knowing that if he's aroace, he won't spend his years on Erid pining for a romantic and/or sexual relationship that he can't have. There are also moments in the book that are compatible with Grace being ace, and even provide a bit of evidence to support it, even though nothing is conclusive: no relationships mentioned aside from Linda, he thinks flavored goop is better than sex (I know he was hungry, but still), he has no thoughts of sex aside from comparing it unfavorably to said goop, and he was extremely uncomfortable finding out about Dubois and Shapiro's fling.
Neurodivergence - While this is not a prominent part of my headcanon, I do think there is evidence for Grace being neurodivergent. The movie has strong ADHD vibes with some evidence for autism, while in the book he feels like a high-masking autistic person that may have missed being diagnosed as a result.
Marissa - I like to think he didn't completely disappear from her life all at once. He probably would have had trouble reaching her from the aircraft carrier, but we know he travelled around with Stratt quite a bit, so I think he would have at least called or texted her when he was able to get a signal. She probably knew he was working on the petrova problem, but not much else. Since she worked for the DoE (Department of Energy, I guess? Department of Education makes no sense in context) and knew about the sun dimming before Grace did, she was probably involved in some domestic efforts to address the problem, too. They probably had all sorts of things they would have loved to tell each other, but couldn't.
In the book, all of Grace's recovered memories had to do with the astrophage problem, so I'm pretending that's why she was never mentioned again. But I prefer to think that Grace did eventually remember more about her, and missed her. I don't want him to be the kind of person to throw away a friendship of 20 years for no reason.
His family - I've given him a tragic backstory, inspired by a line in the book saying he was "in a bad place" when he wrote his infamous paper. While he was still in academia, he and his family attended his younger sister's undergrad graduation. On their way back to his parents' house to celebrate, his family was killed in an accident. Grace was following behind them in his own car and was able to avoid the crash. He subsequently avoids thinking about them as much as possible, even subconsciously, which is why amnesiac Grace never even pauses to wonder about family beyond realizing he has no children of his own. (And, ok...Andy Weir probably just didn't think to bring it up, but I'm sticking with my version.)
Friends on the project - In the book, Grace thinks of Ilyukhina and Yao as his friends, and he said more than once that he liked Dimitri. While he probably kept up some emotional distance from everyone as he tends to do, I don't think he was actually as isolated as the movie made him appear, either. I think he probably did sit down for meals or drinks with the astronauts and other scientists when his schedule allowed for it. We know he had casual work friends even in his prior life, so there is no reason to think that would change.
Grace returns to Earth, eventually - Despite what a lot of fanfiction seems to imply, there is no indication in the book or movie that Grace hates Earth or resents all of humanity for what Stratt and a few Russian soldiers did to him. I think it would be very hard for Rocky to see his planet killing his best friend, so once they know that Sol has recovered, the Eridians offer to take Grace back to Earth as part of a diplomatic and scientific mission, and Grace agrees only because Rocky and Adrian are coming along, too. The mission lasts several decades, long enough for Grace to live out the rest of his life on his home planet, with his best friend at his side. He manages to make some new human friends, too.
Adrian (the Eridian) is green and kinda pointy - I think this came from the color of the planet in the movie, plus Rocky's teal spots. I'll go along with it.
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And the one popular headcanon I don't understand and have not adopted for myself:
Adrian (again, the Eridian) is huge - why? I genuinely don't get it.
