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Andrés Ospina asked this question about Project Hail Mary:
When Rocky gives Grace the little ships models, it says that the atmosphere in Rocky's ship is 29 times the atmosphere in the Hail Mary. But later when Grace is explaining radiation to Rocky he is comparing Erid to Earth and says that the atmosphere of Erid is 29 times as thick. But the atmosphere on the Hail Mary it's 40% of Earth's. Shouldn't be that the atmosphere of Erid is 11 times thick as Earth?
Devon Good catch, yeah there are a few mistakes in the conversation about pressure and you are absolutely correct - Rocky's idea of Earth's pressure is the …moreGood catch, yeah there are a few mistakes in the conversation about pressure and you are absolutely correct - Rocky's idea of Earth's pressure is the 40% pressure he's seeing on the Hail Mary.

There's actually a larger error, when the beads were exchanged, they only compared the oxygen component of Earth air to the ammonia component of Eridian air. It's not clear how Grace jumps to the conclusion that the 1:29 is a pressure comparison and not simply a relative abundance comparison. Why didn't Rocky use strings of nitrogen beads for example? If Rocky had assumed nitrogen was the most imporatn gas, would Grace have incorrectly assumed that Eridian pressure was only 7x higher than the Hail Mary's?

If ammonia is the only component of the Eridian atmosphere, that comparison to Hail Mary air would mean Blip-A's pressure is only about 5.6x that of the Hail Mary and only 2.4x that of Earth.

I assume that the editors might have asked Andy Weir to simplify a more complex conversation about partial gas pressures for the readers' sake, and some of the information got confused.(less)
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Project Hail Mary
by Andy Weir (Goodreads Author)
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