NASA has announced that the ISS (International Space Station) will be deorbited in 2031. Even if this date is moved the space station will eventually deorbit. Once the ISS has broken into thousands of smaller parts, aerodynamics changes. How? What happens to these pieces? How does NASA know they will all land at point nemo?
The reason for targeting "Point Nemo" is that it isn't really a point. The nearest piece of land is 2688 km away. So even if the debris is spread over a 5000 km long strip (and it will be a strip), so long as the center of the debris field is near Point Nemo, nothing of substance will hit land.
Partial answer, and in addition to the already approved answer:
Also, look at When the ISS is de-orbited, what is the likely mass of the largest impact fragment?, as Organic Marble suggests.
Also, from the link BrendanLuke15 provided: https://www.researchgate.net/publication/340902025_ISS_CONTROLLED_DEORBIT_CHALLENGES_AND_SOLUTIONS
What happens to these pieces? How does NASA know they will all land at point nemo?
Because they have done it before, made notes, and the strategy for the International Space Station deorbit is in part based on that experience. But note, they do not state that they expect it to land on that one point, but rather they plan for it to be within a large area (SPOUA), that has, at its center, that point:
Two recent large scale objects controlled re-entry examples include the Compton Gamma Ray Observatory (CGRO) and Russian Space Station Mir.
CGRO was safely deorbited on June 4, 2000. The CGRO deorbit targeted 41 km final perigee and a 5,000 km in-track footprint. CGRO had a mass of ~17,000 kg, and was observed to begin break-up at approximately 72 km.
The Russian Mir Space Station, which was a total of ~130,000 kg when deorbited on March 23, 2001, planned for a maximum target final perigee of 80 km and in-track footprint of no greater than 6,000 km.
Mir was observed to begin aero thermal break-up at approximately 70-77 km (individual module separation estimated at 77 km, massive aero thermal breakup at ~70 km). Russian Mir Space Station so far is the largest manmade object that successfully completed the controlled deorbit into the South Pacific Ocean Uninhabited Area (SPOUA).
Detailed analysis was performed prior to the deorbit to assess Mir Space Station controllability at low altitudes, fuel and thrust requirements as well as system health prior to initiating deorbit operations.
A lot of that experience was used to develop a strategy for the International Space Station (ISS) nominal and contingency deorbit operations.
Note: The South Pacific Ocean Uninhabited Area is roughly centered on "Point Nemo", the location furthest from any land.
Note the annotation above.