
How Sozin's Comet may have triggered the Cataclysm in a giant impact
TL;DR: Sozin's Comet was very close to the planet when it returned during Aang's time: close enough to aerobrake in the atmosphere. If the comet were getting closer and closer to the planet with each passing, it could impact during Korra's lifetime. She will be 47 when the comet returns in 200 AG, which lines up with her age in the ASH teaser. The comet impacting could cause the fires, tsunami, storms, and other phenomena we see in the teaser during the Cataclysm. It could also cause the veil between material and spiritual worlds to tear wide open (perhaps along the path of the three open spirit portals, acting like perforations in notebook paper), merging the two worlds together and causing both permanent physical and spiritual damage.
One of the theories behind what could have caused the Cataclysm seen in Avatar: Seven Havens is that Sozin's Comet may have impacted the planet. I know people have mentioned this possibility before, but this post seeks to explain in detail how the comet could impact the planet, when this would fit in the timeline, and whether or not such an impact could account for the spiritual and environmental disasters witnessed in the ASH teaser.
First, the mechanics of it. We see in ATLA that when the comet arrived in 100 AG it was so close to the planet that it entered the outer atmosphere and its shockwave pushed aside clouds. That is incredibly close for an astronomical body to come to a planet. By entering the atmosphere, the comet likely experienced atmospheric braking, slowing it down to a degree. This is also why the comet erupts in a fireball: friction with the atmosphere.
I posit that the comet may not have always followed the same pattern. Perhaps at some point thousands of years ago, the comet first made an approach close enough to the planet for people to notice. Then maybe due to gravitational perturbations or something, it got closer and closer to the planet each time (returning every ~100 years for only perhaps the last few centuries). Once it was close enough to create a fireball, it granted firebenders immense power on each return (and that power boost got stronger each passing perhaps for the last 500+ years or something ). However, this process would eventually bring the comet in so close that it would be on an impact trajectory.
For timing, the next return of Sozin's Comet will be in 200 AG when Korra is at the age of 47. There is credible context clues to indicate that Korra's age in the ASH teaser is her 40s (see here for details: https://www.reddit.com/r/TheLastAirbender/s/IdTvexkIJr), which would place the comet's return right when the Cataclysm happens. It's possible that the comet comes and goes peacefully and then the Cataclysm happens when Korra is like 49 (or even the Cataclysm happens just before the comet's return), but I find that unlikely considering how well the timeline matches up. It's too coincidental.
So, the final question is whether the comet impacting would actually create the world we see in the ASH teaser? First, I think we need to distinguish between the immediate events of the Cataclysm and the state of the world in the following decades/centuries. Some of the things we see that happened during the Cataclysm are cities on fire, a massive tsunami, and giant storms. If Sozin's Comet hit the planet, it would create a large atmospheric fireball. The shockwave would travel far and do untold damage. The impact would cause earthquakes and volcanic eruptions, and if it landed in water it would cause a massive tsunami. It would also disrupt airflow and atmospheric temperatures, causing massive storms. So, I do think the comet impacting would cause exactly these kinds of catastrophic global phenomena. Not only that, but a large impact from space can definitely ruin a planet so severely that the after-effects could last centuries or millennia.
The main missing component is this: how would the comet impacting cause the spiritual damage / spiritual infusion we see with the later weather disasters? This is the final piece of the puzzle. In the Avatar world, all physical things have spiritual effects. Killing the Moon Spirit stopped people from waterbending, while the return of Sozin's Comet boosted firebending. We also know that the solstices for example represent the material and spiritual worlds being at their closest to one another. When Vaatu entered the material plane, he "pierced the veil" separating the two worlds. Raava chasing after him resulted in the two spirit portals at the poles. They are literally holes in the veil separating the two worlds that allow the direct traversal of inhabitants of either world to the other.
My idea is this: Korra created a new spirit portal in Republic City. The veil was pierced once more, leaving three across the world. Not only that, but all three portals are open now. What if the comet impacting was such a violent physical and spiritual event that it literally ripped a massive tear in the veil separating the two worlds, with the three open spirit portals acting as the weak points in the veil that the tear ripped through (like perforations in notebook paper). This could be the mechanism that causes the physical and spiritual worlds to merge together. Not only would this infuse all of those natural disasters with spiritual energy, but it would permanently affect the world afterwards.
So that's the theory. There could still be other things going on that led to the Cataclysm in some way, such as humanity's abuse of spirit energy or Vaatu's influence, but I still think Sozin's Comet impacting is an incredibly compelling option that fits with everything we've seen so far in terms of possibility, timeline, and effects. I also think it would be incredibly awesome. What do you think?