If we had 10 years warning, we might be able to stop it. If we could get out to it while it was still very far from Earth, it might not take much energy to deflect it. This is why it's important to build systems to detect such objects, like the Sentinel mission from B612.

https://b612foundation.org/sentinel/

Asteroids are tiny in comparison. My example was ~125,000 times the mass of what killed the dinosaurs.

Ceres, the biggest asteroid in the asteroid belt, is only 946 km in diameter, and there are only six larger than 300 km.[1]

Asteroids the size of 300 miles don't just appear out of nowhere. In order for them to hit Earth, they must be coming out of the deep space, and they have to hit Earth (radius 6371 km) out of a circle of radius 1 AU (150,000,000 km).

To put it into perspective, if we can observe one "hostile" asteroid from outside the solar system crossing the circle made by the Earth's orbit every ten years (Note: we've never observed anything like that in our history, and we would surely have detected such a thing with 20th century technology), it will take 10 * (1 AU / 6371)^2 = 5.5 billion years before one hits Earth, on average. By that time the sun will destroy us anyway.

I guess they are still more likely than a group of hostile jerk aliens sworn to exterminate humans once we set our foot on Mars, but not by a wide margin.

[1] https://en.wikipedia.org/wiki/List_of_exceptional_asteroids

I mostly agree with your point as I was mostly going for effect not real risk. Though the earths capture radios is much larger than 6371 km, and odds don't run out like that.

However, the larger point stands. Earth is not completely safe and we really can't protect it from everything.

I don't know, humans are great at blowing stuff up. It's the long-effort over long timespan stuff we're terrible at.

Interesting point on the planetoid. You don't think in 10 years humanity could come up with some strategy to stop the impact?

No, because as he stated before, the thing is going to hit the Earth in 10 years. If you wait around for 10 years, it's already too late. A 300-mile-wide asteroid is huge, that's the size of a dwarf planet. At the last minute, you'd need an astronomical (literally) amount of energy to change its trajectory. Even if we learned of such an impactor today, we'd likely be screwed because our current tech just isn't capable of moving something that big enough, even with 10 years of advanced warning. (I might be wrong about this, but I doubt it; even exploding a whole bunch of giant nukes probably won't change its course enough.) Maybe if we had 100 years' notice, it'd be enough.

Technology will surely improve in 10 years, but the laws of physics won't. It takes energy to move mass, and lots of energy to move a huge mass. I really do not think we're going to invent warp fields in 10 years like they did in the ST:TNG episode with a de-powered Q and use that to magically reduce the mass of the asteroid.

Not even close. Picture a rock that could cover all of Virginia, DC, and Maryland at the same time and tall enough the ISS would hit it.

Honestly, that's sounding pretty good right now.

I'd be interested to see someone do the math, but I'd be curious how much energy it would take to deflect it by hitting it with nukes. It seems like if we could hit it 1 year out it would take well under 1 m/s to make it miss. How much energy that would take, I have no idea.

1m/s * 1 year = 31,556.926 kilometers considering the earth has gravity I don't think you could really go much lower than that unless it was really close to missing us in the first place.

https://en.wikipedia.org/wiki/Ceres_(dwarf_planet) is is a little smaller than that and estimated at 9 x 10^20 kg. So call it 10^21kg.

KE = 1/2 m * v^2 (mass in kg, v in m/s = joule) but a bomb is not 100% efficient call it 50%. So, 1/2 * 10^21 * 1^2 /50% = 10^21 joule.

Largest bomb ever detonated is = ~2.1×10^17 J so ~5,000 of them is kind of an ultra optimistic estimate. Not that we actually have 5,000 of them. Worse each of those weigh ~60,000 lb so we now need build rocks, and even build the infrastructure to build the rockets to get 300,000,000 kg out there not just LEO.

At a rough ballpark 1/2 the worlds GDP for 8 years is not going to get you there. Worse that 50% was crazy optimistic.

Forgot to respond, but nice analysis! Thanks! Interesting how it comes out to something definitely infeasible, but still in the approximate realm of the world's nuclear capability (~16k of various sizes exist today).

The rocketry there would seem to be the impossibly limiting factor.