Comment by nkrisc | Hacker News Reader

Comment by nkrisc | Hacker News Reader

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For anyone else curious who wants some tangible sense of the dangers, the Tunguska impactor is estimated to have been 50-60m in diameter [1]. The impactor that created the Barringer Crater in Arizona is estimated to have been about the same size [2].

Regarding a 100m asteroid impact:

> The pressure blast would destroy buildings up to 9 miles (15 km) from ground zero, and windows would shatter more than 60 miles away (100 km). To make matters worse, as the partially burned rock hit the ground, it would trigger seismic tremors that would spread through the planet's crust, carrying the destruction further away from the epicenter. The debris ejected into the air by the force of the impact would rain back on the ground miles away from the impact site, and the finer dust and dirt would remain hanging in the air, spreading with the wind across large distances.[3]

I can imagine a 140m asteroid causing a very, very bad day indeed for a region.

Not an expert, just curious and I can type stuff into a search engine.

[1] https://en.m.wikipedia.org/wiki/Tunguska_event

[2] https://en.m.wikipedia.org/wiki/Meteor_Crater

[3] https://www.space.com/asteroid-apocalypse-how-big-can-humani...

I wonder, could an asteroid be traveling at a relative-to-Earth speed of very slowly, so that the impact most like just "setting down" on Earth rather than slamming into Earth?

There is minimum amount of energy from falling down Earth’s gravity well. Earth escape velocity is 11 km/s. A big chunk of asteroid energy comes from Earth’s gravity.

On the other hand, the orbital speed of Low Earth Orbit is 8km/s. Thus, with regard to asteroid redirection missions, we'd need 'only' about 3-4km/s of Δv to prevent this 'gently setting down' asteroid from hitting the Earth by capturing it into orbit.

Definitely into science fiction territory here considering that DART resulted in a Δv measured in centimetres per second, but I'm still rather tickled by the idea of collecting a new moon for ourselves :)

If we don't need to capture it to orbit, but just avoid hitting the Earth, centimeters might be enough. The trick is to be able to do it way in advance.

Besides, why LEO? Even GSO is 11 times closer than the Moon.

You're quite right - attaining GSO would indeed require only another 3 or 4km/s. But it does seem a little unfair to put it in GSO; we'd surely want people in both hemispheres to get a chance to gawk at our new satellite!

Taken that most of the Earth surface is empty uninhabited lands and oceans -- no biggie. Most probably.

Probably. Usually.

I can even say "Always". So far, 100% of 50m+ asteroids hit uninhabited areas. Statistics :)

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