Asteroid question

So an asteroid did a fly by. Exciting stuff.

But one of the articles I read brought up the blowing up an asteroid concept. And went onto explain that it wouldn’t do any good. I’ve heard that before and even read it hear I believe. But I don’t understand it. Small asteroids burn up in the atmosphere before striking earth, right? So why wouldn’t blowing up a larger asteroid into smaller parts have the same effect?

Roughly speaking, an asteroid/meteor smaller than ~25 m (80 ft) will burn up in the atmosphere. But there is no simple way of breaking up a large asteroid so that every piece is smaller than that. Even a 40m asteroid (upper limit given in the OP’s link) will need to be split into at least 3 evenly sized pieces for them to all burn up in the atmosphere.

And even that number is a rough ballpark figure, and depends on the composition, relative speed, etc.

Even if one of the pieces was still big enough to strike the earth, wouldn’t a small piece cause much less damage?

The shock wave from the Chelyabinsk meteor caused some damage on the ground, mostly broken glass. There were also some reports of flash blindness causing vision injuries from the light of the meteor. It also injected a bit of dust into Earth’s atmosphere, and obviously heated up the portion of the air it traveled through. According to Wikipedia the Chelyabinsk object had an estimated mass of between 12 and 13 million kilograms.

The Chicxulub impactor had a mass of between 1.0×10[sup]15[/sup] and 4.6×10[sup]17[/sup] kg (again from Wikipedia). If our team of intrepid astronauts blows a Chicxulub-sized object into Chelyabinsk-sized chunks, there will be between nearly 77 million of them (at the low end of the size range for Chicxulub and the high end for Chelyabinsk), up to over 38 *billion *of them (at the low end of the range for Chelyabinsk and the high end for Chicxulub). The shock wave and flash damage from tens of millions or tens of billions of Chelyabinsk-level events happening at nearly the same time would be pretty overwhelming; plus, with that many of the things all hitting at once, the effects from atmospheric heating and atmospheric dust are no longer going to be purely theoretical things that can be maybe calculated but not really felt–those effects will now drastically affect the climate of the whole planet.

As the saying goes “Quantity has a quality all its own”.

An asteroid that burns up in the atmosphere is striking the Earth. It’s striking the thin gaseous part of the Earth, not the hard rocky part, but that doesn’t make any difference: It’s still dumping all of its energy into the planet.

But the way it dumps its energy does make a difference. Particularly how scattered it is.

Years ago, I heard that if you set off a paint bomb and change an asteroids color, that will be enough (because of the change in light pressure) to shift it into a different orbit and miss Earth. I assume this would only work if you had a few years lead time, but if the asteroid was due to hit in 2040 or so, that would be plenty of time.

https://en.wikipedia.org/wiki/Yarkovsky_effect

That’s more than I can really get, When I heard it, I was picturing it in terms of one of these (boy I hope this link works), a toy from my childhood which I find easier to understand.

ETA Crookes radiometer - Wikipedia. Never knew what it was called.

To put it simply, would you rather be shot with a rifle or a shotgun? Both are pretty bad. Just because a ballistic object is broken up doesn’t mean the kinetic energy is. In fact, I suspect, though I am no expert, turning an asteroid bullet into a bunch of asteroid buck shot pellets may make the hypothetical “nuclear winter” even worse. Also, it’s SURE as hell going to make the initial heat flash worse.

The key in asteroid defense is to bend it so you don’t have to deal with the kinetic energy at all.

Different effects. Yarkovsky is caused by asymmetric photon emission (and is very, very weak). A radiometer relies on uneven heating of the minute amount of air inside the bulb.

I would think NASA would use a mission to divert it’s path, whether an explosive or hitting it with a heavy object.

How would you do it though? If it’s a tiny asteroid, just big enough to reach the ground, then splitting it in two may prevent either piece from reaching the ground. But how would you split an apartment-building size boulder in space? Drill all the way to the middle and plant a bomb there?

But the asteroid responsible for the K-T extinction event was likely 10-15 km in size. To break that into 25 m size means breaking it into 100 million pieces of roughly equal size. How??

Yes I’ve read that analogy many times. It doesn’t make sense to me. If I was a half a mile away, I’d rather be shot at by a shot gun. Can you see why? The analogy just doesn’t hold.

I’ll be the first to admit my ignorance of these things but as I offered earlier, wouldn’t smaller sized chunks burn up before hitting the earth (and yes I realize the atmosphere is part of the earth, but asteroids that burn up in it don’t cause the damage that the ones striking the ground do - note I am talking about small ones that burn up, not big ones that explode above the surface)?

Also, I’m not suggesting that we have the capability to see them far enough in advance to send a fleet of nukes out to blow them up. I’m merely addressing the hypothetical that these discussions comment on - namely that blowing one up wouldn’t help the situation.

One hundred tons of space debris enters Earth’s atmosphere every day (mostly in the form of dust). For the low end estimate quoted above for the mass of a Chicxulub-sized object, that means reducing it to “dust” would still have the equivalent of over 27 million years worth of normal daily meteoroid debris getting dumped on us, if not instantaneously then over a very short period of time.

Piling on, and with credit to Chronos, who I remember first making this argument here…

The Chicxulub impactor had between 1.3E24 and 5.8E25 J of kinetic energy. https://en.m.wikipedia.org/wiki/Chicxulub_crater This guy estimated the heat capacity of the entire atmosphere to be about 6E21 J/K. https://scholarsandrogues.com/2013/05/09/csfe-heat-capacity-air-ocean/

IOW, if all of that energy were converted to heat, the atmosphere would raise in temperature anywhere from 500 to 10,000 degrees K.

Now that obviously isn’t the whole story—a lot of that energy is going to be reradiated to space, the oceans have a much greater heat capacity, etc—but it should show that dumping all of that KE to atmosphere is still suboptimal.

One advantage of turning the mountain to gravel is that the velocity imparted to the gravel should mean that a lot of the gravel will miss.

This is it.

If you let this impactor hit in one piece, it delivers nearly all of its kinetic energy to the ground. Massive dust cloud, possible crustal tsunami, lotta crying and dying.

If you shatter it into a gazillion pieces that completely vaporize in the atmosphere, it delivers all of its kinetic energy to the atmosphere, raising it to/beyond broiler temps. Everything wilts and dies and/or is possibly incinerated before enough heat radiates to space or is absorbed by ground/ocean to cool the atmosphere back down to survivable levels. Lotta crying and dying.

Why are we going straight to Chicxulub?

There is a legitimate idea here. If an asteroid of dangerous size is going to hit the Earth, should we break it apart to reduce the danger, or dismiss the idea entirely because it won’t work on the single largest asteroid impact we’ve ever discovered?

How about something Tunguska sized? I’m going to bet that a couple of bunker busters will do a fair amount of damage to a rock 200 feet in diameter, and maybe spread the energy of the 20MT impact over a wide area instead of letting it be concentrated on a city or turn into a tsunami.

In other breaking news, a bullet proof vest won’t protect you from a howitzer.

Instead of fragmenting it, and getting hit by some of the spall, how about moving the asteroid, and getting hit by nothing at all? (Hold on: we still get to use the nuke.)

From Stranger On A Train, and apologies in advance for my butchery in paraphrasing his stated idea: if you want to use a nuke to move the asteroid, use it to vaporize a puck of polyethylene next to the device, and let the momentum from that now quickly moving plasma cloud move your Rock of Doom. If the nuclear device can have its radiation directionally biased, as opposed to radiating uniformly in all directions, even better.

Getting the nuke and puck next to the object in time to sufficiently move it away from an Earth collision, is an exercise for the reader.

For your Tunguska rock, it doesn’t even matter if it strikes the Earth…provided the impact is over an ocean or similarly uninhabited area. Satellites catch kt level air bursts from bolides all of the time.
No one cares because they’re over the ocean, at 200,000 feet or so, or both.

Something like Apophis, hitting an average depth of ocean with a ~1GT of TNT impact, is going to cause a minor tsunami 500 miles away or so. You wouldn’t want to be within 100 miles or so of the impact, and there are places where even a 6 foot tsunami will kill a shitton of people, plus I’d think global weather would be messed up for at least that year, but it wouldn’t be the end of the world.

What are the odds today?

KillerAsteroids.org says not to worry. :smiley: