Why was The Martian's NASA lecture on earth at "Day 1"?

After The Martian Mark Watney got rescued and returned to Earth, there is a scene near the end where he sits on a bench and looks at a little plant emerging from the ground to his feet, reminding him of the plants he had to grow himself on his exile. Then he stands up and goes to lecture to some NASA students while the screen reads "Day 1", in contrast to all the "Sol X" we saw on Mars.

However, this was clearly not Mark's first day on Earth, seeing that he would have to go through serious medical and public treatment after his return and not just start a new job as a perfectly healthy NASA lecturer right away. It is thus unclear as to what that "Day 1" actually applies to exactly. Is it related somehow to the plant he sees growing (seems unlikely, as the "Sol X"s weren't related just to the plants either)? Is it just his new job at NASA (which would seem a bit superficial to me)? Or was it merely left as "Day 1" instead of, say, "Day 34" to keep the emotional impact of the 1, willingly ignoring the question of some reasonable counting base? Has there been any comment on this or at least some reasonable deduction based on the movie or on evidence that eluded me? Or does the novel maybe even give some hints where the movie doesn't?

the-martian

Best Answer

I interpreted it as the first day for Mark in his new mission of training future astronauts. This also has nice symmetry with the Sol count, since Sol 1 was the first day on Mars and therefore the start of the Mark's mission on Mars.

I think this ties in nicely with the new plant because it is basically a new beginning/phase/chapter in Mark's life. Also the plant is a kind of bridge between Mars and Mark's new job. On Mars Mark had to use his knowledge, including botany, to survive. Based on what I recall of Mark's speech to the trainee's, Mark's new job/mission was to teach them how to survive.

In the current version of the book, with Matt Damon on the cover, the story ends when Mark enters Hermes. I've heard that an earlier version of the book has some scenes on Earth, but I didn't read it so I can't say if there's an answer there.