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Comment by EamonnMR | Hacker News Reader

Detect it early enough and we can nudge it out of our way with a large rocket. Problems include: solar system is big, comets have really long orbital periods, we need to be good enough at predicting the path to be sure that the nudge is putting it in a good orbit we like and not setting us up for disaster. We do look for asteroids with the impression that if they ever found one coming out way we'd do a mission to stop it (though I don't think that's a real commitment.)

See: https://en.m.wikipedia.org/wiki/Asteroid_impact_avoidance

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The dinosaurs really messed up by not having a space program.

If they really wanted to survive, they should have prioritized colonization of Mars over their silly interspecies zero sum resources-based conflicts.

If you can survive mars you can survive asteroid scoured earth.

Well, there a is a theory that dinosaurs evolved into a transwarp capable species, now residing over in the delta quadrant...

[0] https://memory-alpha.fandom.com/wiki/Voth

Detect it early enough and we could just paint it, apparently just a significant change in albedo will change the orbit over time.

I don't think we have a proven paint-in-space technology but we definitely have proven 'hit with rocket' technology.

Yeah, but hit it with rocket won't change the orbit of any object that might cause the civilization serious problems.

Even nukes have a surprisingly small effect, unless they are buried. We have landed on on an asteroid, but have yet to embed a nuke in one.

The trick about nukes is you have the risk of just making an harder to stop by making a cloud, like say comet levy which turned into 21 pieces, but delivered the same total energy when hitting the atmosphere.

The nice thing about the paint is that it's not that hard, even asteroids have gravity, and we have orbited (very slowly) asteroids before. It doesn't cause the astroid (which might just be a loose collection of rocks) to break up, and you get a huge win per pound of delivered mass, granted it takes months or years to accumulate into a large orbital change.

I would think a broken-up asteroid would be better, in that the worst possible outcome would be exactly the same as not hitting it, with all the pieces undisturbed enough to still hit the earth.

However there would be more surface area to burn up in the atmosphere, and if you do it far enough out and I'd think it would require very little nudging to move pieces out of the way

Sure, if 50% of the mass of the resulting explosion burns up in the atmosphere it's a huge win, but maybe not enough. But if it was as big (or bigger) than the dinosaur killing object (there's some debate if it was a comet or asteroid), it might just split into a few pieces that will come through the atmosphere intact.

Generally if it's a planet killer you want to take no chances. The earlier the detection the better, and changing the albedo will work if it's a sand up to a solid rock.

I've heard similar proposals with a "gravity tug", but it's not clear to me that it would work with a significantly larger change in velocity than just using the fuel directly. Keep in mind that the asteroid that killed the dinosaurs was approximately 10km (some sources) to 15km (other sources) across, and we have no reason to think that future asteroids might not be bigger.

The largest atomic crater I could find was from a 104 kiloton bomb that created a 400m wide and 100M deep. Both the USA and Russia has similar tests, and that would be just a small dent in a 15km across asteroid. Both were from 100-200m deep explosion, and it's not clear if deeper would necessarily be better. Sure you might crack a 15km long asteroid into two pieces, but it wouldn't help much. Vaporizing a 15km asteroid is going to take WAY more than 100 kiloton.

What might work is some kind of nuclear engine that melts stone/sand/ice and ejects it at high velocity, working it's way into the center of the asteroid. It would need a throttle to only fire when it helps and idles when it doesn't.

What about 50MT? Tsar bomba hit that. Geopolitics aside, is larger possible?

If your asteroid or comet manages to get broken up into many smaller fragments, but all or most of them still reach the earth, but are small enough to burn up in the atmosphere before impact, their total energy would still be transmitted via atmospheric entry friction heat, which itself could cause lethal global air temperature increases. They might last only a few minutes or slightly more but (the science on this is a bit ambiguous) we could still be talking about temperatures going up into the hundreds of degrees. No big bang, but still catastrophic for crops, plants, forests, people and atmospheric health.

Oumuamua wasn’t detected until after it passed by the Earth so it’s a hard challenge to detect from far away.

I believe it came a close as 0.16 AU (tracing the path backward), which is 66 times further than the moon.

Being an interstellar object though, it moves faster than the escape velocity to the sun, so it would pack a higher energy per unit of mass than a regular comet or asteroid. Fortunately such objects are also somewhat rare.

OK, crazy idea time.

Couldn't we detect such things with radar? Given the right frequencies, rocks and dirt will reflect - that's how terrain-following radar works.

So yes, I think we could, but there are some significant problems.

1. 1/r^2 power loss, in both directions. We would need a massive radiator, and very sensitive detectors.

2. The detectors are in the wrong place. You send out your signal, and several hours later the response comes back, by which time the earth has rotated. So where your detector has to be depends on the distance to the object, but you don't know the distance to the object!

So we'd need a bunch of detectors at various points around the globe. And we'd need a huge power source.

Which brings me to solar flares. They emit radio waves. Do they emit enough power at the right frequencies to be useful for this?

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