What would happen if asteroid 99942 Apophis collides with the earth?

In the news recently it's been said that in 2029 the asteroid called Apophis, aka 'The God of Chaos', will fly by very close to earth. To quote Geek.com

In 2029, a massive asteroid called 99942 Apophis will fly past our planet at an approximate distance of 19,000 miles within the distance of some orbiting spacecraft.

It's said the chances of a collision are about 1 in 100,000, which is small but not not completely infeasible either.

The asteroid has a diameter of around 350 meters with a mass of 4×10^10 kg and an average orbital speed of around 30km/s.

What kind of damage could we expect on earth if it were to collide with us?

• I guess the chances given for a collision are based on a uncertainty of the computations 10 years into the future. The closer we get the more certain the projections get, as orbital mechanics is a completely deterministic system. May 3, 2019 at 22:11
• There are various online calculators that can do impact analysis, eg impact.ese.ic.ac.uk/ImpactEarth/index.html May 3, 2019 at 22:41
• Wikipedia's entry for 99942 Apophis has a summary of the rough impact effects it would have. But there are a huge number of variables (e.g. hits the ocean, continental coast, the Antartic, the angle of impact). For this reason I'd call this too broad of a question. Broadly speaking bit crater, possibly lots of dead people (millions) and human life will continue away from the blast. Huge economic impact if it hit some places (e.g. China's silicon valley or a main oil producing area). None if it missed them, Too broad a querstion. May 4, 2019 at 0:51
• You have mis-read part of the article. Apophis will not have a 1/100000 chance of hitting Earth in 2029. The chance it will hit Earth is 0, or at least as close to zero as we can determine. We know where it will be in 2029, and it won't be hitting Earth. It has a very small chance (1 in 100000) of hitting Earth at some point after 2060. May 4, 2019 at 21:29
• It has a very small chance (1 in 100000) of hitting Earth at some point after 2060... I'll be dead or senile by then so I'm not concerned. Apr 28, 2020 at 3:08

1 Answer

If it hits the deep ocean, not much relatively speaking. In the recent past, people wildly exaggerated the capability of an asteroid (at least ones in the size range of Apophis) to cause massive tsunamis; in reality, the ocean efficiently and quickly absorbs the impact. That said, it'd still be terrifying to see such an impact in deep water.

If it hits a city, it would cause violent devastation, immediately killing 10's or 100's of thousands with its initial impact, and millions with the resulting shock wave and debris.