Asteroid hit.

August 31, 2007 6:24 AM

Would we get enough warning to get out of the way if a big asteroid is bound to hit Earth? How big does an asteroid have to be to be visible for an extended period before it enters atmosphere?
posted by spacefire to science & nature (26 comments total)

I may be misunderstanding the question, but we couldn't "Get out of the way", no matter how much warning we had.
posted by qldaddy at 6:38 AM on August 31, 2007

This talk from astronaut Rusty Scheickart, will answer alot of the questions you might have about the possibility of an asteroid threat.

The Asteroid Threat Over the next 10,000 years
posted by hector horace at 6:50 AM on August 31, 2007

I should have been more specific. Yes, to leave the estimated point of impact or coastal areas if it hits an ocean and generates tsunamis.
posted by spacefire at 6:54 AM on August 31, 2007

A sufficiently large asteroid will wipe out all complex life on Earth. They even have a name for this: an Extinction Level Event. It's been talked about enough that they even abbreviate it to ELE.

Short of an ELE, if you'd like a reasonably accurate, 1980s-style look at the possible consequences of a major strike, read the 1980s novel Lucifer's Hammer.

They'll be able to tell as long as a couple of years out that we might get hit, but if it's the most common type of body, a comet, they won't know for sure that it will hit us until it actually does. Why? Because comets are constantly burning off mass from melting -- that's what makes the long tail -- and this throws off any orbital calculations. And the boiling and outgassing makes the thing wobble around pretty good. By orbital standards, 25,000 miles is a tiny distance, well within the margin of error, but it's the difference between a direct hit and a complete miss.

Asteroids are a lot easier to predict, being rocky, but they're a lot harder to see. It's easily possible for an asteroid to sneak up and hit us without being detected.

If we detected an asteroid out far enough, we could tell you what hemisphere it would hit, and probably could get the area within 5,000 miles or so... but when the asteroid hits the atmosphere, precisely what will happen is not at all clear. As far as I know, about the best we could say it, "Well, we think it'll hit somewhere in the United States." So no meaningful evacuations are really possible.

We probably could evacuate coastal areas if it were going to hit an ocean; the tidal waves from a major meteor strike would wipe out whole coasts. Think of the Pacific tsunami from a couple years ago, except scouring, say, San Francisco and Los Angeles right off the map.

There's absolutely nothing you can do about this, so it's not worth worrying about. But if it makes you feel better, the Earth is very small, space is very large, and there aren't very many bodies left with eccentric orbits that cross ours.
posted by Malor at 6:56 AM on August 31, 2007 [7 favorites]

I'm sorry if I came off snarky. I should have asked for clarification.
posted by qldaddy at 6:58 AM on August 31, 2007

They'll be able to tell as long as a couple of years out that we might get hit

Unless it comes at us from our blind spot.
posted by mediareport at 6:59 AM on August 31, 2007

It's easily possible for an asteroid to sneak up and hit us without being detected.

Without being detected until when?

Just curious.
posted by letahl at 7:07 AM on August 31, 2007

Something big enough to cause a deadly wave but small enough not to kill us all probably would be hard to track. Surprise!

But "to get out of the way" could mean more than a trip to the mountains. With good enough data and modeling, we might know for a long, long time (years) that a big, predictable asteroid eventually is going to wallop the Earth and kill everyone. That might give us time to launch a handful of people into space and maybe far enough away to avoid debris.

Where those few would go after that is anyone's guess. In a self-sustaining ship, they might coast practically forever (or until something hit the ship). Maybe they'd launch themselves into an orbit that would bring them back around (like a comet) in a few years to see if Earth might be inhabitable again. A few people could repopulate the place again fairly quickly, assuming the giant cockroaches didn't eat them first.
posted by pracowity at 7:16 AM on August 31, 2007

Lost in the shadow of Armageddon was Deep Impact, released around the same time, which indeed has a story element based around the acronym ELE, evacuation, etc. Given your question, you might find it interesting.
posted by WCityMike at 7:20 AM on August 31, 2007

We might not get enough warning. Asteroids like this are measured on something called the Torino scale. My understanding is that asteroids commonly get their ratings changed. I'm not sure how it works but a far off asteroid may be a candidate for hitting earth and as it gets closer astronomers can detect the likelyhood of this. An asteroid that was in the news a couple years ago as being an earthkiller (forget which was) was downgraded to harmless recently. So the system is far from perfect.

As mentioned upthread there is also a blindspot.

On top of that, there's no getting out of the way. Its impossible to predict where on earth its going to hit. Even if it hits an empty area, the soot from fires or whatever could fill the sky for weeks, thus causing freezing temperatures and mass extinction like the dinosurs. Or it coudl cause an incredible tsunami.

There's some research on pushing these things slightly out of the way, but thats still in the territory of mostly science fiction.
posted by damn dirty ape at 7:28 AM on August 31, 2007

There's a scale of impact danger called the Torino Scale. Some guys at NASA keep track of possible collisions here, but it's too technical for me, at least at first glance. According to a museum in Berlin, the Museum für Naturkunde, the asteroid "99942 Apophis" will come close to us on April 13, 2029, and on March 16th, 2880 the asteroid "1950DA" might collide with us. The museum paints a much rosier picture than Malor and doesn't seem to think that asteroids can sneak up on us; we just can't tell, from this early on, whether or not they'll really hit us. So according to these guys -- not me -- we have at least 22 years' warning. Also apparently the crater diameter is typically 10-20 times larger than the projectile, so it would probably suck.
posted by creasy boy at 7:28 AM on August 31, 2007

Also, I definitely don't know what I'm talking about, but according to my source here: asteroids hit the earth once ever 3000 years on average.
posted by creasy boy at 7:33 AM on August 31, 2007

Major News About Minor Objects with lists of current items. Nothing in sight right now, really. This site lists data from two projects, one at NASA and the other in Europe. Both projects look at newly discovered objects and try to predict the path of the object about 100 years into the future. Beyond 100 years, we typically don't have enough data to say anything. And of course, something *could* appear with no warning at all.

NASA JPL on the subject. Further searching should turn up guesstimates of "there are probably n objects out there, we know about x percent of them, and we'll have them all catalogued by year z". Maybe someone else can fill in the variables. Note that some discussions include a strong hint that z can be reduced with extra funding.

This book is a great read on the subject, with lots of factoids and scenarios. Author's assertion: you shouldn't worry about giant Earth-destroying rocks so much as the more likely Tunguska-sized events or somewhat smaller ones. If the Sikhote Alin event in 1947 had happened over a populated area instead of remote woodlands, it would have been a major disaster.
posted by gimonca at 7:51 AM on August 31, 2007

They absolutely can. In 2002, we had a very near miss, and we didn't see it until three days after it went by. It came within the orbit of the Moon, but nobody saw it. You can read more here. The article says it was 'big enough to devastate 2000 square kilometers'.

The bigger asteroids are, the more damage they do, but the more likely we are to detect them. It's unlikely that anything literally Earth-shattering is going to sneak up on us, but the relatively little stuff easily can.

Even a little one that hits in the ocean could be a big, big problem.
posted by Malor at 7:52 AM on August 31, 2007 [1 favorite]

Dammit, I hit post too soon. I was gonna add.... sounds scary, huh? We humans incorrectly assign scariness to big events that we can't control, no matter how remote the probability is.

You would be much better off worrying about dying from sharkbite.

If you just wanna THINK about this, it's really fun and interesting, but in terms of true WORRY? Not even worth it.
posted by Malor at 7:56 AM on August 31, 2007

where "near miss" meant about 20 earth radii - which means 1 in 1000 similar events actually hit us.

(is it reasonable to call that a "near miss"? it's a bit like saying a car on the next block is a "near miss" when i cross the road).
posted by andrew cooke at 8:32 AM on August 31, 2007

Well, it came six times closer to us than the Moon. I'd say that's a damn near miss, personally.
posted by Malor at 8:37 AM on August 31, 2007

where "near miss" meant about 20 earth radii - which means 1 in 1000 similar events actually hit us.

(is it reasonable to call that a "near miss"? it's a bit like saying a car on the next block is a "near miss" when i cross the road).

That logic is flawed. The proportion of a car to the earth is much less impressive than that of the earth to the rest of the universe. There is also the matter of relative frequency of the event, and of course the consequence.
posted by letahl at 9:09 AM on August 31, 2007

your whole argument seems a bit odd, but out of curiousity, and given that asteroids are solar system objects:

size of car approx 1m
size of earth approx 5,000,000m
size of solar system approx 5,000,000,000,000m

car/earth = 1/5,000,000
earth/solar system = 1/1,000,000

to within errors they're actually about the same (i had no real idea how it would come out before looking up the numbers)
posted by andrew cooke at 9:33 AM on August 31, 2007 [1 favorite]

Nemsis, maybe it is time?
posted by yoyo_nyc at 9:40 AM on August 31, 2007

One extra bit of info is that while driving and missing/or being hit happens primarily in two dimensions, the Solar System is in 3D. Most objects are along the ecliptic, but there's a pretty good amount of wiggle room "up" and "down", likely a few hundred Earth diameters in both directions.

As a vague, handwavy guess, I think your earth:solar system comparison would be more accurate at 1:1 billion.
posted by Malor at 10:15 AM on August 31, 2007

Note that the Earth actually zips around pretty damn fast. It takes about 7 minutes for our planet to travel a distance equal to its diameter. That means that if you detect a large object on a colision course a ways in advance its not actually such a huge task to alter its course enough to prevent a disaster. Slow it down so it would arrive 7 minutes later and its a miss.
posted by Riemann at 10:42 AM on August 31, 2007

for some reason at this moment in time i would like to jump in front of a bus.

now you might think that, to be sure of killing myself, it should be a huge, heavy, high speed rolling along crazy sandra bullock at the wheel kind of bus. but no! those are the ones that will easily avoid me....
posted by andrew cooke at 10:53 AM on August 31, 2007

I thought your numbers were off, so I went back and ran them myself; they were indeed two low, but the ratios between a car to the Earth and the Earth to the orbit of Neptune (since we just redefined the Solar System to be a lot smaller) are startlingly similar.

Neptune's orbital area is 63.711 * 10^19 km2. (I'll write these with the eXX suffix from now on: 63.711e19)

Earth's equatorial radius: 6378km. The area of a circle drawn through the equator: 127,796,483 km2.

Neptune's orbital area divided by Earth's 2d displacement: 4.98e12, or about 4.9 trillion to one.

Earth's surface area: 511,185,933 square kilometers.

For ease of use, I'll assume a car is about 10m2. 10 m2 in square kilometers is 1e-5, one ten-thousandth of one. So the ratio of Earth's surface to the area of a car:

5.11e13, or 51 trillion to one.

So the two numbers are off by about one order of magnitude. Earth takes up about 10 times as much of the solar system as your car takes up of Earth. If you assume just 'of exposed land', not counting the depths of the Pacific as a possible car location, then it's only about three times as much.

At least, it does if I ran the numbers right, I'm not practiced at this anymore. :)

Of course, I've completely ignored the fact that most of Earth's surface isn't paved, and thus doesn't have any cars at all....
posted by Malor at 11:02 AM on August 31, 2007

is it reasonable to call that a "near miss"? it's a bit like saying a car on the next block is a "near miss" when i cross the road

If you think in terms of how much the object's vector would have to change to hit, the asteroid probably really was a very near miss. Or in terms of how much time we missed by, especially relative to the potential harm.
posted by ROU_Xenophobe at 11:36 AM on August 31, 2007

for some reason at this moment in time i would like to jump in front of a bus.

now you might think that, to be sure of killing myself, it should be a huge, heavy, high speed rolling along crazy sandra bullock at the wheel kind of bus. but no! those are the ones that will easily avoid me....

I see what you're getting at (that Sandra Bullock is an excellent bus driver), but how does that relate to asteroids and comets?
posted by !Jim at 2:34 PM on August 31, 2007 [1 favorite]