These are notes from a presentation by Henry Spemcer at Capricon 46. Any mistakes here are mine, not Henry’s. I have amplified my notes with web links for further clarification. Here is the blurb from the convention program:

Near-Earth asteroids (and their cousins, comets) are interesting objects, possible future sources of metals and other materials… and potential threats to civilization and even life on Earth. The good news is, this is the only type of major natural disaster that we might actually be able to prevent. A look at what we know about asteroids (and comets), what sort of threat they present, and what we can do to anticipate trouble from them and maybe head it off.

First type of natural disaster that could be prevented (soon).

Edmond Halley suggested that a comet might hit the earth, and the consequences could be bad.

The asteroid belt: Ceres + debris.

Near Earth Objects (NEOs). Atira, Aten, Apollo and Amor. Based on properties of their orbits. See NEO Basics

Moons of Mars. Possibly originally asteroids, but how did they get into such close orbits of Mars.

Chiron: Asteroid or comet.

Kirkwood gaps. See also Diagrams and Charts: Asteroid Main-Belt Distribution

Most meteorites are stone, not Ni/Fe. Spectra of asteroids and meteoroids can be obtained. See Asteroid spectral types

Chelyabinsk meteor of February 15, 2013. Diameter 17-20 meters. Blast equivalent to a 400-500 kiloton bomb. Fortunately it exploded at an altitude of about 30 kilometers/18.6 miles. See also Teaching about Hazards in Geoscience. The Chelyabinsk meteor came almost out of the sun in an almost horizontal approach. A more vertical approach would have caused a lot more damage.

Tunguska event. June 30, 1908. Equivalent to a 3—50 megaton bomb. Biggest such event in recorded history.

Prehistoric Events

• Chicxulub crater. The dinosaur killer.
• Hiawatha crater
• Possibly a Hudson Bay crater, the Nastapoka arc

Apophis will pass close to Earth, inside geosynchronous orbit.

Infrared is better than visible light for finding and sizing asteroids.

Double Asteroid Redirection Test (DART) tested the possibility of deflecting an asteroid by direct impact. It successfully changed the orbit of the asteroid moonlet Dimorphos. See also What Was DART?.

It is better to slow down or speed up an asteroid than to hit it from the side.

What about using a big Hydrogen bomb to destroy an asteroid? You still might end up with some big fragments on a collision course with Earth. Also, it has been a long time since a really big H-Bomb was built. See Tsar Bomba. You would also need a big rocket to carry it, something like a Saturn V.

Another idea: Attach an ion drive to the problem asteroid. Very low thrust, but if you run it long enough you could change the asteroid’s orbit sufficiently.