Meteorite crash in Russia

D H

You are misinterpreting. That "has cleared the neighborhood around its orbit" clause doesn't mean that every last bit of stuff has either been swept up, ejected, or captured as a moon. It means almost everything. IIRC, a planet-like body is deemed a planet if the mass of that planet-like body is 100 times more than the mass of all the other stuff that orbits in the same orbital zone as the body in question.

There are plenty of small solar system bodies that orbit in the same orbital zone about the Sun as does the Earth. The total mass of all of those bodies doesn't come anywhere close to the mass of the Earth.

Oldfart

Almost free, relative to development of an effective early warning system that can detect incoming meteors, would be an advertising effort that simply explains that it's necessary to seek cover away from windows in the event of a brilliant flash of light.

I suspect that many of the injuries were caused by people going TO windows after the flash to see what was going on...

Jimmy Snyder

Does this help?
2010 TK7

russ_watters

Bob, I don't know if you've changed your position or if I misunderstood earlier, but your examples of the earth sweeping out its orbit and Saturn's rings lead me to think that you were under the impression that all near-earth asteroids would necessarily hit earth/earth's atmosphere significantly below escape velocity. Edit: note, you continue to use wording that implies you think all NEOs would impact at a speed below escape velocity: Do you really mean 'could result in an impact at less than escape velocity if properly perturbed just prior to impact'?

If all you meant was that if some event like a close encounter with the moon perturbs its trajectory just before it hits earth (or bouncing off the atmosphere or getting hit by a nuclear bomb), an asteroid could hit the earth a little below escape velocity, then we're all good. The paper I linked mentions the effect of the moon. Heck, the moon has its own mass and escape velocity and will often act to increase the impact velocity on earth!

russ_watters

Very cool. Something else I learned: http://www.space.com/15151-earth-mul...asteroids.html

Now we'll have to quibble over the definitions of "moon" and "asteroid" as it pertains to object size.

Jimmy Snyder

Here is a contrived, but possible situation. An asteroid hits the Moon a glancing blow and is sent from there to a point just past the Earth-Moon L1 Lagrange point with a velocity nearly zero w.r.t. the Earth. At what speed will this asteroid hit the Earth? Neglect air resistance.

D H

And longevity. Those chaotic orbits aren't very stable. Moons are things that are more or less permanently resident. (Some of the moons of Jupiter are dubious as "moons".) Those objects drift into the vicinity of the Earth inside what's called a weak stability boundary. They come for a visit, but they don't stick around for long.

A couple of examples of such temporary moons: J002E3, which turned out to be the upper stage of the Apollo 12 spacecraft, and 2006 RH₁₂₀, which is a natural satellite.

NASA recently used weak stability boundary transfer concepts to get the GRAIL satellites to the Moon. Instead of going directly to the Moon, the satellites went out almost to the Sun-Earth L1 point and then fell back toward the Moon on a ballistic capture trajectory. The 3 to 3.5 day journey to the Moon used by the Apollo program became a two month long slow drift, but saved a whole lot of fuel. (The so-called Interplanetary Highway System would be more aptly named as The Interplanetary Conestoga Wagon Trail. It's never fast to use those weak stability boundary transfers.)

aquitaine

Ok, what tax breaks do Planetary Resources get? They do have significant private investment from such people as Larry Page, Erich Schmidt, James Cameron and some other highly successful people. Show me where there is significant government intervention specifically for them.

And not one of those governments that is "encouraging" action actually has a realistic plan to do it. Denmark has been spending huge amounts of tax money on wind farms. And 20 years later the percentage of electricity generated from coal is still 80%, higher than China's. There's a very basic reason for this, fear of nuclear power. This actually goes towards my point because it's a long running irrational hysteria. Germany in the past ten years has spent 100 billion Euros of tax money on solar alone plus a rather substantial amount of tax money on wind farms. So when it shutdown all of it's nuclear power plants (because of that fear factor I mentioned) despite the truly stunning amounts of money spent on the green saviors they ended up with major shortfalls in electricity production, an unstable grid, and skyrocketing electricity costs. So what are they going to do about? Why go back to COAL and NATURAL GAS of course. In other words, more fossil fuels. All because of fear. You can make people afraid of almost anything for a surprisingly long period of time as long as you control the narrative in a way that preys on their ignorance.

The reason the other governments aren't so into it is because most of them are poor. They want to develop their economies and that's what their constituents also want. The difference here is the narrative and in developing countries they don't have the same levels of fear mongering about this, so that's not high on their list of priorities. Interestingly enough one of the effects of this is to render all of our CO2 control efforts, ineffectual as they often are, a complete waste of time. Even if our carbon emissions went to zero it wouldn't matter because the growth of the third world.



That wasn't my point. My point was that the means are private now which has reduced the costs of launching a probably government paid for asteroid pusher thing into space pretty significantly, which does matter a lot.

BobG

Perhaps you have misunderstood my position, since this started with a post where I agreed you were essentially correct, but only because the probability of an impact at less than escape velocity was so incredibly low - not because they were impossible.

Which eventually prompted your reply....

But it isn't impossible and the perturbation doesn't have to occur just before impact (at least not if you mean the type of duration described by being perturbed by the Moon just before impact). It's original orbit has to be altered so that it's new orbit is almost the same size as the Earth's orbit, it's orbital plane has to be very close to the Earth's orbital plane, the trailing object has to be slightly lower than the leading object's position as they approach towards the collision - and the collision practically has to happen on the first close approach of the two objects, since the orbit of the asteroid is going to be drastically changed by the close approach. (Or perhaps an asteroid starts out not meeting those criteria, but a close approach changes the orbit to meet those criteria.)

It has to be an asteroid that has moved into the Earth region recently, since the Earth tends to clean out debris too close to its own orbit. While that happens continuously (or else we wouldn't have as many near earth asteroids as we do and also means "clearing the neighbourhood" is an unending task, as DH pointed out), the probability of altering it to meet the criteria for a low velocity collision makes "very unlikely" an understatement.

Actually, I think I did say, or at least implied, that there was a time in the past (early in the solar system) that low velocity impacts were common (even if a very low percentage). They aren't common now.

OmCheeto

"D" sounds plausible, based on the numbers.
With an orbital period of 240,000,000 years for the sun to go around the galactic center, we should look for clues around that time period in the past.

It looks like we transitioned from the Paleozoic to the Mesozoic eras around 250,000,000 years ago. Did anything special happen back then? I'm not much of a historian. Lot's-o-space rocks maybe? This might be fun. I've never seen a big meteorite before.

hmmm....

Oh my. I think I'll stock up on canned beans and toilet paper.

russ_watters

I'm still unclear. It still sounds like you are saying that an object can approach from a long distance (say, 10 million km since its last major interaction), not interact with the moon on its way in, and hit earth significantly below escape velocity and that a significant class of NEOs fit that description, regardless of if we've cleared most of them out (note: according to the paper I linked, these are still the most likely objects to hit us).

Or put another way, it sounds like you think an unperturbed trajectory (again, of at least the last 10 million km) exists that can cause a below escape velocity impact and that most or all NEOs that hit us have such such a trajectory by definition of being NEOs. It doesn't make sense to me that you used the Earth sweeping out its NEOs as an example unless you think a significant fraction of them (all of them?) Impacted at below escape velocity.

Could you please try to answer more succinctly because all of the qualifiers you are putting on this don't add clarity and seem to contradict your examples.

D H

Yes, that is possible Russ. Significantly below escape velocity? No, but below is possible. Likely? No. It's rather unlikely. It is not, however impossible. It is impossible in the context of the two body problem (the Earth, the asteroid, and effectively nothing else). Add a big third body, i.e. the Sun, and things get weird.


It's a small fraction of NEOs that fit this description. The vast majority that impact the Earth will do so with a velocity greater than escape velocity. Saying that all of them will isn't quite true, but it's pretty close to being true. It's close enough to being true that a lay article can legitimately say that it is true.

Regarding the paper you linked, the authors didn't write clearly, which in turn led you to misread/misinterpret what they wrote. This is, I think, the bit from that article that you are interpreting incorrectly:

Most asteroids snagged by Earth's gravity don't zoom around our planet in neat circles, according to the simulation. Instead, they follow complicated, twisting paths, tugged this way and that by the gravitational pulls of Earth, the moon and the sun.

That "snagged by Earth's gravity" was not alluding to the asteroids that impact the Earth. It was alluding to the very, very few asteroids that, at least temporarily, orbit the Earth. Most (almost all) asteroids that impact the Earth aren't "snagged by Earth's gravity" (i.e., orbiting). They came in to the vicinity of the Earth on a hyperbolic trajectory and they would have immediately have left on a hyperbolic trajectory had the Earth not have been in the way.

What that part of the article was alluding to is that it is unlikely to capture an asteroid and have it end up in a circular orbit. Very, very unlikely. For example, the "captured asteroid" explanation for the moons of Mars has come under increased scrutiny because this explanation doesn't make sense from a dynamical point of view.

g.lemaitre

If the Russian meteorite released 20 Hiroshimas of energy, then how come only two people were injured? I'm guessing they're measuring energy from the time it entered the Earth's atmosphere until it hit the ground, whereas the Hiroshima Bomb released all of its energy right at one time, the meteorite released its energy over a long period of time. Still, that doesn't sound like a good explanation to me.

Borek

Not necessarily - it is a matter of distance from the explosion.

Borg

As Borek stated, it's the distance. And there were 1200 people injured - mostly from flying glass. The main shock wave was strong enough to blow out windows all over the city but only one building's roof partially collapsed. If it was a little bigger, this event could have been a lot worse. Also, it's been reported that there were three separate shock waves. The first one, along with the initial flash got everyones attention. Then, when people went to look out the window, the second shockwave hit strong enough to blow the windows in their faces. Nature can be unforgiving sometimes.

OmCheeto

And I would imagine, duration. The meteor would have been dissipating energy the entire time, from entry, to disintegration. Does anyone know how far it traveled through the atmosphere?

hmmm....

from my calculations, this meteor arrived with a speed of 17.8 km/sec

Earthsky.org lists these numbers for various showers:

ref

Bah! Lame! Slower than a Draconid!

BobG

If there's a lot of debris sharing the Earth's orbit (as there was early in the Solar System), then there's a lot of collisions. Low velocity impacts are still the exception, but there's still a lot of them.

You can't have an unperturbed trajectory. Both the asteroid and the Earth are orbiting the Sun and the Earth is perturbing the asteroid's orbit (and, likewise, the asteroid is just slightly perturbing the Earth's orbit).

To glance at the orbits of near Earth asteroids, you'd say a lot of them look pretty similar, but having a similar size isn't enough. They have to match other parameters as well. And they have to collide before their orbit is changed again.