“Don't wake me for the end of the world unless it has very good special effects.” -Roger Zelazny
It's always the ones you least expect that get you the worst, it seems. I went to bed last night excited that Asteroid 2012 DA14, a 200,000 ton asteroid, was going to pass within just 28,000 km (or 17,000 miles) of Earth's surface, which would make it the closest pass of an asteroid that large that we've ever observed.
Image credit: NASA / JPL Near-Earth Object Program Office.
I thought that would be the best way to celebrate today, which would be Galileo's 449th birthday. After all, it was Galileo who first discovered that there was no way that Earth could be at the center of all the heavens. By looking at Jupiter through a telescope, he discovered that it had its own set of large moons that very clearly orbited their own planet, indifferent to the workings of Earth.
Image credit: Damian Peach of http://www.damianpeach.com/.
We now know that these moons orbit Jupiter because of Jupiter's gravity; this is the same reason all planets, moons and solid objects move the way they do in space. Jupiter is the second largest gravitational source in our Solar System, behind only the Sun. And since it's been orbiting the Sun for over four billion years, it's had literally hundreds of millions of passes by each object in the asteroid belt.
Image credit: NASA / ESA / STScI.
Every solar system has an asteroid belt, and here's why: as you move away from the Sun (or any star), the temperature of the interplanetary space around you drops. Near the planet Mercury, interstellar space is somewhere around 800 °F, out by Pluto, it's nearly -400 °F. But there's a critical place -- out beyond Mars but before Jupiter in our Solar System -- where the temperature is too cold for water to exist in any state other than frozen ice.
And once you reach that point, you're going to get little frozen chunks of ice and rock mixed together. So every solar system has an asteroid belt. But ours also has a large planet nearby, and over billions of years and millions of passes outside this asteroid belt, Jupiter changes the orbits of these rocky objects.
Image credit: Jen Christiansen. Via NASA Jet Propulsion Laboratory.
And these repeated gravitational interactions of asteroids with the other planets -- primarily Jupiter -- changes their orbits over time. This is important to us here on Earth for a few reasons, but nothing makes it more apparent than seeing the havoc a collision with one of these asteroids can wreak here on our world.
Image credit: D. Roddy, U.S. Geological Survey.
This is meteor crater, from an asteroid strike about 50,000 years ago, of an asteroid that was comparable in size (maybe 50 meters in diameter) to 2012 DA14, the one that just missed us today. Asteroids of this size -- 40 meters or larger in diameter -- strike Earth a couple of times every 100,000 years, and could wipe out an entire London-sized city if they struck there.
One of the big problems is that we only know of about 1% of the asteroids that are that size, so we can't even tell when most of them are coming. It's only the ones that we get a good view of for a long time that we can track well enough to predict when they're going to strike us. The hardest ones to predict are the ones that come towards us from the direction of the Sun; we literally never see those coming.
Image credit: Mark Oliver from the UK's Telegraph.
Which is why it was such a shock when this meteor appeared in the skies over Russia early this morning!
Take a look from a different view; this is what happens when a roughly 50-tonne asteroid -- a mix of ice, rock and other chemicals -- enters the Earth's atmosphere.
The physics of what's going on here is amazing. Let's do some Q&A about this:
Q: Why does it make a fireball in the sky?
A: The Solar System is a fast-moving place. Most objects move in excess of 25,000 miles per hour relative to Earth, and you probably think the wind was problematic when you put your arm out of the window while driving down the highway! At the astronomical speeds achieved by meteors, the outside of the meteor heats up tremendously, by many hundreds of degrees, and the fire you see is from a heat so hot that the meteor is disintegrating before your eyes.
Q: Why does it appear to explode in mid-path?
A: Because it really does explode! Think about it: you're heating this mostly frozen ice-and-rock-ball by hundreds and hundreds of degrees. Inside the meteor, you've got frozen water, frozen methane, and other weird, carbon-rich molecules. What happens when you heat these ices up? They melt, and eventually boil. As this boiling causes fissures in the meteor, oxygen -- common in our atmosphere but rare everywhere else -- can combine with these combustible gases under very high heats.
And that combination of things very quickly goes boom.
Image taken long enough ago that copyright has expired. :-)
Q: Why -- like this one and the Tunguska event -- do so many of these occur over Russia?
A: They don't preferentially occur over Russia, if that's what you're asking. Events like these -- I call them super-bolides -- occur on average about once every few years. There was a comparable one, another 50-100 ton asteroid, that encountered our atmosphere and burned up over Indonesia in 2009; in reality, most of them occur over the ocean and so go unobserved and unrecorded.
The Tunguska event was special: it's the largest one in recorded history, and was probably just a little smaller than the asteroid that made meteor crater. The reason these feel like they occur over Russia is simply because Russia has a huge amount of land area.
Image credit: NASA / JPL-Caltech.
Q: Why didn't we see this one coming?
A: First off, it's small. It's very difficult to see something that's just two-three meters across until you get very close to it, even with the most powerful telescopes in the world. Even the most ambitious survey proposals of asteroids that could be potentially hazardous to Earth don't go smaller than about ten times the volume of this one. And second off, it came from the direction of the Sun, the hardest direction to monitor. (Because if you're going to build an expensive telescope, the first rule is do not fry your optics, which you'll do if you point it too close to the Sun!)
Image credit: Meteosat-10.
Q: THIS IS A HOAX! IF IT WAS REAL WHY DIDN'T NASA PHOTOGRAPH IT FROM SPACE?
A: NASA doesn't monitor all places on Earth all the time from space. But this part of the world was actually monitored at the time, by the EU's Meteosat program. Above is the image of this meteor event from the Meteosat-10 satellite.
Image credit: Oleg Kargopolov / AFP / Getty Images.
Q: How much damage did it cause, and how did it happen?
A: There was some localized property damage, and probably around 1,200 injured people. When the big "flash" (or explosion) occurs, both a sonic boom and an intense pressure wave emanate from the source. This can do things like blow out windows (imagine the damage if one hit New York City!), damage eardrums, and -- in the case of Tunguska -- knock even large objects completely over. The building above had its roof collapse from the blast.
But this doesn't destroy the meteor, it just breaks it up into smaller chunks. Many of these fragments reach the surface, still traveling at speeds that are often in excess of terminal velocity and capable of causing some pretty intense damage, similar to a cannonball strike. The ice, below, had this giant hole created in it from a meteorite fragment.
Image credit: Chebarkul town head Andrey Orlov.
So what you hear reports of come from a combination of the initial blast wave and the secondary falling debris.
And finally...
Image credit: Don Davis.
Q: How long before the big one strikes, and all of humanity dies?
Believe it or not, an event like the one that caused the mass extinction of the dinosaurs is thought to occur only every few hundred million years. These events occur at random, which means -- like getting struck by lightning -- there's no way to predict it, not with our current state of knowledge.
But we could know this, what we'd have to do is find and start tracking each one of these potential Earth-killers, or any asteroid larger than a few kilometers in size. And we could do it with our current technology, too; all we'd have to do is invest in it.
Want to hear more about this meteor and have even more of your questions answered? I'll be on my local TV station tonight at 7 PM Pacific Time, and you can watch it live from anywhere in the world! See you then! The video permalink is up here, and you can watch the segment embedded below!
UPDATE: Just got my hands on this information, courtesy of Peter Brown, the director at the Centre for Planetary Science and Exploration in Canada and one of the world's experts in meteor fireballs. Be aware that these numbers are still preliminary, and many of them -- especially the size, mass and yield -- may change.
What follows are *initial* information gleaned for multiple instrumental sources recording various aspects of the Feb 15, 2013 airburst over Chelaybinsk, Russia (55.2N, 61.4E)
1. Time: The time of the main flare/airburst was 03:20:26 UT on Feb 15, 2013; the fireball began ablation about 30 secs before this time.
2. Based on the long duration of the event and videos, it is clear this was a very shallow entry (certainly less than 20 degrees, maybe more shallow).
3. It is *not* related to 2012 DA14
4. Energy: This is perhaps the hardest value to pin down so early in this investigation. From multiple sensors using multiple technologies a best initial estimate of the total energy of the event is about 300 kilotons of TNT equivalent = ~10^15 J). This could easily be in error by a factor of two. I am confident, however that it is in excess of 100 kTons, making it the largest recorded event since the 1908 Tunguska explosion.
5. Speed: The fireball entered the atmosphere at 18 km/s
6. Damage: The airblast clearly caused window breakage and light structural damage in downtown Chelaybinsk. The exact overpressure at which window failure occurs tends to be probabilistic and varies by construction design (ANSI S2.20, 1983). Normally some damage begins to occur around 500 Pa of overpressure, widespread window damage is expected to occur up to around ten-20 times this value. As the fireball had a shallow trajectory, the cylindrical blast wave would have propagated directly to the ground and would be expected to be intense. This could be further compounded by any fragmentation, quasi-spherical blasts. My impression is that the key here is that the terminal part of the fireball (probably between 15-20 km altitude) occurred almost directly over Chelaybinsk; this was perhaps the single greatest contributor to the blast damage (short range to the main part of the terminal detonation).
7. Comparators: The Sikhote-Alin fall (Feb 12, 1947) in the former Soviet Union was the equivalent of about 10 kilotons TNT, BUT as an iron impactor much of this energy was deposited at the ground rather than at altitude. The Oct 8, 2009 Indonesia event is the most recent similar event at about 50 kTons, but over the ocean (paper attached for quick reference).
8. Size: The pre-impacting asteroid was about 15 meters in diameter and had a mass of ~7000 tonnes.
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And your blog couldn't have a more appropriate name today :)
The figures I read were 15M diameter, 7000 tonnes, a few hundred kt of energy, exploding about 12 miles up. When I heard this energy and height figure it didn't make sense to me as I would imagine the shockwave hitting the ground with a lot more force than what the videos showed. Then again, I imagined this force radiating out spherically from a point.
Is it more appropriate to think of the shockwave radiating our cylindrically from a line?
I second critter42's comment. Maybe "Starts With a Bang and Ends With a Bang!".
A lot of people were injured by the flying glass.
http://www.bbc.co.uk/news/world-europe-21468116
The flying glass injuries from this event reminded me of the Halifax Explosion of 1917. That event had two ship colliding in the harbour which drew a crowd, with many watching through their windows from the safety of their homes. Unbeknownst to almost all, one of the ships was laden with explosives destined to the WWI theatre in Europe. What ensued was what has been quoted to have been the largest man made pre-atomic age explosion. In addition to the ~2000 deaths there were hundreds blinded by flying glass. The charity Canadian National Institute for the Blind (CNIB) was formed shortly after in Halifax.
I'd expect many eye injuries from this Russian event.
Thanks for your timely blog on the meteorite today Ethan - enjoyed your explanation as always (although with no equations to make my head hurt which I actually enjoy). Ironic to go from your prior peaceful sunset post to today's literally explosive topic!
Hi Ethan,
your data: " Asteroids of this size — 40 meters or larger in diameter — strike Earth a couple of times every 100,000 years,"
isn't really in accord with other sources. Wiki states much more frequent times.
"Objects with a diameter of roughly 50 m (164 ft) strike Earth approximately once every thousand years," source "Record Setting Asteroid Flyby". NASA Science. Jan. 28, 2013. Retrieved 2013-01-29.
and there is a table also on wiki with mass/diameter/frequency of impact.
4 m (13 ft) 3 kt 0.75 kt 42.5 km (139,000 ft) 1.3 years
7 m (23 ft) 16 kt 5 kt 36.3 km (119,000 ft) 4.6 years
10 m (33 ft) 47 kt 19 kt 31.9 km (105,000 ft) 10.4 years
15 m (49 ft) 159 kt 82 kt 26.4 km (87,000 ft) 27 years
20 m (66 ft) 376 kt 230 kt 22.4 km (73,000 ft) 60 years
30 m (98 ft) 1.3 Mt 930 kt 16.5 km (54,000 ft) 185 years
50 m (160 ft) 5.9 Mt 5.2 Mt 8.7 km (29,000 ft) 764 years
70 m (230 ft) 16 Mt 15.2 Mt 3.6 km (12,000 ft) 1900 years
85 m (279 ft) 29 Mt 28 Mt 0.58 km (1,900 ft) 3300 years
this isn't really couple of times during 100.000 years. So who's data is correct? :)
Imagine being able to say that a scar in your face was caused by an asteroid. I am jealous.
@Sinisa: I must admit, reconciling that gave me a bit of trouble. But I think it comes down to the heading on that table (hoping formatting works here, or this'll be ugly): "Stony asteroid impacts that generate an airburst". I.e. they don't actually "strike Earth". And they aren't the rarer iron-nickel ones, like the one that created Barringer Crater that Ethan was talking about. So, in their respective ways, they're both right.
The question of "why Russia" came up in conversation today, and yeah, the answer is pretty obvious when you think about it. Russia is *big*, about a tenth of the earth's total land area. If a chunk of rock is going to land on any country, they've got the worst odds...
@ Randy
I wasn't under the impression that Ethan talked about a certain types of asteroids. In fact am pretty sure he didn't. And on NASA's site (as far as impact probabilities).. there is no talk of composition.
more from NASA's site: 2012 DA14 is a fairly typical near-Earth asteroid. It measures some 50 meters wide, neither very large nor very small, and is probably made of stone, as opposed to metal or ice. Yeomans estimates that an asteroid like 2012 DA14 flies past Earth, on average, every 40 years, yet actually strikes our planet only every 1200 years or so."
... again.. this is long way from 100.000 years.
Ohh, small mistake in one of the figures: http://scienceblogs.com/startswithabang/files/2013/02/MarkOliverTelegra…
The telegraph got the GPS satelites wrong. What they ment were TV-satelites in geo-synchronous orbits. GPS is not geo-synchonous, they run at approximately 20,000km, orbiting earth in 12 houres.
Cheers,
Semmel
I would suspect the colloquial "couple of times" rather than the mathematical couple.
More than one, less than several.
@ Wow
I was under the same impression in the beginning. But this is actually 100 times more. I can't accept 100 times more as "couple of time". Maybe Ethan meant to say "couple of times every 10.000 years"... but 100.. :/
Aye, but frankly I can't be arsed being at all bothered about it.
It's a benefit of using a wavey term like "couple".
@AJ Ah, yes. The Mont Blanc explosion. An incredibly interesting story. I have the book about it around here somewhere.
Sinisa
You are correct and Ethan seems to have misplaced a factor of 10 in meteor size or a factor of 100 in the frequency.
Ethan says, "Asteroids of this size — 40 meters or larger in diameter — strike Earth a couple of times every 100,000 years, and could wipe out an entire London-sized city if they struck there."
Whereas:
A Tunguska event is a 1000 year event (50 to 100m meteor)
http://geology.com/articles/near-earth-asteroids.shtml
A 160 m impactor that could destroy (NY or Tokyo) is a 5000 year event.
http://nineplanets.org/meteorites.html
Keep rocking the kilt Ethan! Represent the Utiliclan!
Ethan, you should write a follow up post about the B612 Foundation's efforts to privately fund a space telescope, called Sentinel, to catalog NEOs (Near Earth Objects).
There are 2 challenges with searching for NEOs: you can't search in the IR from ground based telescopes due to atmospheric absorbtion, and you can't look up at the daytime sky to see many of the objects you might hit. Sentinel will operate in a Venus type orbit, looking outwards from the Sun.
My understanding is that most (~90%) of the >1km sized objects have been cataloged (they're easier to see). NEOs follow a power law with regards to size vs. population (smaller objects are more numerous), and it's the objects that range between 50m-1000m that are of great interest; while they're not life-ending events, the equivalent of a 100MT bomb can cause quite a bit of devistation. With enough advanced warning, it doesn't take much to push them into a benign orbit.
The Foundation is looking to raise ~$500 million for the telescope, which is comparable to large municipal projects like metropolitan museums, stadiums, and such. Ball Aerospace has been chosen as the prime contractor, leveraging their experience with Kepler, Deep Impact, Spitzer and cryo-cooler technology. It's a mature and sound proposal. It's a worthy non-profit to make a donation to, and they still need everyone's help to meet their funding goals.
The NYT article talked about infrasound, ~ <20 Hz, which they consistently confused with a shock wave which would have lots of high-frequency energy. Also your basic sonic boom propagates as a cone with the generator at the vertex ... but the picture I get is that as the bolide travelled through the atmosphere it generated a lot of low-frequency rumble like a thunderclap which I can imagine generating a lumpy but energetic "field" of acoustic energy which developed nodes that sometimes coincided with glass (etc) objects, exploding them by resonance rather than overpressure. So I as my usual question: reasonable thought?? (ps, how long is that contrail? Eg, over what distance was the bolide distributing acoustic energy?)
"But we could know this, what we’d have to do is find and start tracking each one of these potential Earth-killers, or any asteroid larger than a few kilometers in size. And we could do it with our current technology, too; all we’d have to do is invest in it"
Excuse my lack of spirit when it comes to scientific inquiry or at least this particular issue but what would be the point? It's not as if we could do anything about it? Frankly I'd be happier not knowing when the big one is going to land.
Yes we can.
Early enough and you can change the orbit of any asteroid with any level of push you can manage.
@Wow,
Even if we couldn't push it out of a collision orbit, wouldn't breaking up a large "extinction level' astroid, into smaller "regionally damaging" fragments be possible if we used our nuclear arsenal (finally a GOOD use for these weapons!), or am I watching too many scifi movies?
@ Sean T
It's possible in principle to break up an asteroid enough that each individual fragment would be small enough that it would break up in the atmosphere and that which did make it to the ground would be comparatively minor.
It's vastly more likely in practice, particularly with an extinction event asteroid, that you simply break it up into pieces still more than large enough to make it to the ground intact delivering the same amount of energy as before, and thereby have accomplished nothing.
Or, even more likely than that is you have no noticeable effect on the asteroid at all.
Blowing up the asteroid is a bad choice. There's simply too much mass in a big one for even the biggest nuke ever to disrupt it significantly.
Moving it is a much better choice. And this is completely feasible, even for very big rocks, with today's technology. Had Apophis proven to be a danger, it would have taken a 1-ton gravity tractor spacecraft using ion thrusters (or any highly efficient low thrust engine) approximately 2 years to move it sufficiently to keep it from passing through the keyhole.
A laser ablation system would also work. Use the asteroid's own material as reaction mass as it's vaporized off the surface to push it out of the way.
A kinetic impactor would also work. Just slam a high velocity object of a goodly mass and let Newton's Laws do the work.
You might once again be thinking "nuke it!" but that's actually a poor way to transmit momentum to the object.
All the practical methods of moving an asteroid have one common property: They require time to work. This is why detection of potentially dangerous objects is so crucial. We need to know years in advance so we can launch a mission and have time to be effective.
Of course it also helps if we have a mission developed, tested, and ready to go if we need it. Add all the R&D time to the necessary lead time if we wait until we find one to start working on it.
The problem with nuking is two fold:
1) you still need a shitload of bang, more than we have for an ELE asteroid.
2) you need to put that bang INSIDE, otherwise all you're doing is heating a bit of the surface.
Nuclear explosions devastate because they cause a supersonic shockwave in the earth's atmosphere. There's no atmosphere in space.
But put some chemical or ion (if we have enough time) on it and Bob's your Uncle.
Wow and CB,
Thanks guys, looks like I have been watching too many movies. Although, I did realize that a surface blast would have little effect; a buried nuke was more what I had in mind.
I'll see if I can dig up a post from t'internet with someone doing the maths of how little even a buried nuke would do to just about any large asteroid. The short of it is you'd have to put LOTS in there (or else they just hang around together) and right in the middle (or else you'd at best end up with a smaller radioactive asteroid).
What if we insisted on using nukes (cus hey, we have 'em and we can't use 'em here on earth so why not). I'd wager the best tactic would be to explode them nearby the asteroid, not to disrupt, but to push.
Same principle as the laser ablation, only vaporizing a larger quantity of material all at once. I once did some very rough calculations to try to show that a nuke isn't a good weapon for space combat (due to lack of air), but ended up getting a pretty decent thickness of steel vaporized from a nuke exploding 1km from a space ship. I of course made ludicrously simplifying and generous assumptions, like that all energy was in a form that solid steel would absorb, but that vaporized steel would not so it could reach full depth.
It might be interesting to do some better math and see if there's any possibility there. While I could probably do some research to figure out the energy fractions in the various types of radiation that steel absorbs, I have no idea how to realistically model the actual interaction with a surface as its being vaporized. :/
The push would from a nuke be unnoticed, really. Not much would be vapourised, nor would it be of great motive power.
The proposed Impulse drives for stellar travel use a small nuclear explosion done very often. Not one honking big one, and they only use that because you can get somewhat higher efficiencies from the higher temperature of the fused pellet than you'd get from a chemical reaction. You don't want photons: you want it to remain in the material left behind after fusion.
Put ion drives on it and solar panels and ablate the asteroid substance for material, powered off the solar panels. Greater efficiencies than any other drive and if we have an orbit or two, we can use chaos theory to give us a bigger shift. by timed chemical/nuclear blasts.
Great Post. keep posting!
http://www.intuitor.com/moviephysics/
This one goes into all stupid movie physics.
Right, me and my friend are having a debate on whether the meteorite hit the building (in one of the above images) or was it a fragment of it? or was it even the sonic boom of it entering the atmosphere??
Thank you.
I have a tsunami question. to stop a tsunami, couldn't you add a material to stretch the shoreline making the back of the tsunami fall in front of the front of the tsunami making it collapse on it's self? a tsunami become very dangerous, when it hits the shoreline, because the back catches up with the front making it very tall and thus you see the giant wave.