No Stupid Questions

Let's suppose some fun-loving aliens lower that rock slow enough that touchdown isn't some cataclysmic event. We now have an asteroid 60 Km across at its widest point sitting on the Earth's surface. That surface will immediately start to experience the pressure you'd find 60 Km deep in the Earth. There are places on Earth where the solid crust extends lower than that, there are others where that's inside the mantle.

The weight might crush the crustal plate into the mantle, in which case the effect will be very much like a supervolcano going off. Smoke, toxic gas, exploding rocks tossed hundreds of kilometres. It'll last decades or possibly centuries. Chances are, you've enjoyed your last hot fudge sundae.

But maybe the crust is strong enough to support the weight - until a few hours pass and it starts to melt from pressure and heat. As it melts it compresses and flows, sending stress through neighbouring seismic fault lines and causing earthquakes, regular-size volcanic eruptions and tsunamis across a vast area. It may not be enough to destroy the environment, but it'll be serious enough make everyone forget about global warming as an issue.

This is speculation. I'm neither a geologist nor an asteroid the size of Corsica.

It wouldn't

Earth's gravity would make it accelerate from a far away distance and when it would hit, it hit with speeds greater than a bullet.

An entire large island hitting earth at those speeds usually means game over for humanity and maybe even all life in this universe

Not that we'd need any help in doing that, were perfectly capable of doing that ourselves

If you’ve ever ran into a kid at low speed in your Land Rover defender it’s probably like that.

Imagine a large rock, suspended by helicopters a few miles up in the air.

Now drop the rock. How fast is it going when it hits the ground?

The same thing is true for a rock falling from space, but more so. Regardless of initial conditions: if it ever contacts the ground, it will be moving at least 11 kilometers per second.

Pick up a tiny asteroid and drop it from 1m. It hit the ground slightly faster than a reversing truck.

Pick up a bigger one and drop it from orbit it's going to go faster.

Whatever you drop won't be an asteroid because it's already on earth.

So if you pick up corsica and drop it on florida from less than a meter up (they had it coming) there would be a mass extinction in florida. Everything under corsica would die, buried under a mass of rock, mud and whatever. If it did not die already because it could not squeeze into the less than a meter gap between the masses. There would also be an earthquake, maybe a tsunami if some of it fell in the ocean.

The thought experiment goes past everyone's point on gravity eventually creating a velocity that is devastating. What would such a mass (between 100 and 180 km in diameter based on map of Corsica) do if it just magically settled gently onto a land mass and then gravity came into play? It wouldn't be extinction level, but there are lots of regional effects to consider. Weather patterns would be a huge one. Continental plate deflection, which would affect ground stability and water flow. Certainly earthquakes if anywhere near even smaller fault lines. A change in Earth rotational speed and wobble.

it would speed up due to gravity so yea still dangerous probably. it it somehow didn't speed up then it'd be fine

Depends on the energy being exchanged but the earth is absolutely massive so probably not much. It might cause some movement of the crust or something.

Theoretically, probably not a great experience for the people some 300mi away or closer but I don't think it would be an extinction level event. Speed is how most of the energy gets transferred. Lower speed, smaller boom.

I think it has to stay theoretical though. You would have to turn gravity off though or make the asteroid such a weird shape that air resistance slows it down to that speed before it hits. And I think it would have to be sail-like at that point hitting at the right angle, making its impact much less threatening and making it way more likely it would've burned away in our atmosphere anyway. Before it hits earth there will be gravity pulling on it, most effectively from the sun and then earth. So even if cosmic forces got it to reverse beep beep beep speed before it enters earth's gravity well, which I would call unlikely with an asterisk, then it would speed up 9.8 m/s or 22 mi/h every second it falls from the heavens. Thus making the impact more impactful than reversing speed. The asterisk being that there is a much bigger other new body in space that exerts enough gravity on the asteroid to slow it down. Which means it's close enough to mess earth up in other ways (tidal waves, megaquakes, etc.) even if it does not also hit us, which I would assume it does though if it got this close already. So then we're back in extinction territory whether Corsica hits us or not.

Guessing you mean the speed of a truck relative to the speed of the Earth, as the Earth is traveling around the Sun much faster than a truck

Ok everyone - let's say there's a gigantic anti-gravity machine attached to the asteroid so that it actually does hit the earth at the speed of a truck backing up. What happens to the earth?

My first thought is, shit would get real fucked up before it even hit the ground. A rock that's thousands of miles in diameter sitting extremely near the earth for days as it very slowly approached the surface would cause serious gravity effects, like local tides would be completely fucked.

In terms of impact i think it would be pretty much just F=ma equation. According to a few rough estimate numbers i put into ai, it says the object would have 2.4x10^20 joules of kinetic energy. To put that in perspective, the nuclear bomb in Hiroshima released only 63x10^12 joules

Assuming it was going the speed of a reversing truck, it would still pick up speed when it got close enough to earth. Less destructive than hitting at 25,000 miles an hour but still pretty destructive

Gravity alone would start causing problems before it boops the planet

There's no such thing as "slowly" when it comes to that much mass.

This really can't happen, but most of the consequences would probably be volcanic at that size. The sudden pressure from a lump thicker than the Earth's crust would cause earthquakes and probably set off volcanoes.

Lots of people would die from the chaos and likely ensuing volcanic winter, but we'd mostly get by. If there's anything valuable in it like a mountain of platinum, conflicts over its resources could be more deadly than the impact.