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Ebyl
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Reged: 07/04/12

Re: Meet DA14's little brother? new [Re: Scott Horstman]
      #5686390 - 02/18/13 02:58 AM

Keep in mind that a meteor like the one over Russia has almost no chance of getting anywhere close to the ground. I'm not even sure what scenario would cause one like it, and of similar size, to "explode" near the ground, let alone reach it. And chondrites make up about 85% of all meteorites found, so we know they're by far the most common.

My point here is that while meteors of this size and a bit smaller certainly pack enough energy to cause considerable damage (500kt is a scary number at first glance), since the majority are chondrites they will not get the chance. Now, an iron or stony iron meteoroid might be a different story. But they are much, much rarer - something like 5-6% of meteorites found, I think.

I would also say I think we are getting a good grasp of how often these types of events happen. Infrasound detectors have incredible ranges, so I doubt any event of significant size escapes their notice. And that's to say nothing about things like satellite and radar detection of meteor events. Of course, that's only useful for the smaller meteoroids, since the larger ones are so infrequent as to require study by whatever impact craters we can find.

In the end, while I think we'd be well served with an increased push in detection efforts, I'm not sure the cost to benefit ratio is there for asteroids of this size. They are insanely difficult to detect and the vast majority would never cause any significant damage. I don't think the picture is quite as grim as the numbers appear on the surface.


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Jarad
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Re: Meet DA14's little brother? new [Re: Qwickdraw]
      #5686636 - 02/18/13 09:10 AM

Quote:

I may not understand the whole concept but do know that given the correct mass, speed and altitude of an object you can have it swing all the way around a planet and leave orbit again, ala Apollo 13 or any number of other examples.




The issue is the speed. Both objects were coming in at high speed, well above orbital velocity. So while the earth's gravity could have deflected their orbit a little bit around the equator, not that far north. And certainly not that far north and heading south (a full 180 degree reversal).

Again, I gave Ravenous props because he noticed the correct issue, even before the additional info about the actual heading of the bolide.

Jarad


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shawnhar
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Re: Meet DA14's little brother? new [Re: BillFerris]
      #5687098 - 02/18/13 03:04 PM

Sorry Bill, I meant the rare form of fully functioning no correction needed extra digits.
My point was that just because 2 rare events happen within a short timeframe doesn't mean they are related. (Unless the event repeats) I will concede that some event(s) in the asteroid belt could have led the close timing, but we don't have any evidence for that, in fact the evidence leads away from that supposition. These 2 events are related in the way that every movement in the solar system is gravitationaly affected by everything else but I don't think we will find direct interactions leading to these 2 visitors arriving so close in time.


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Scott Horstman
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Re: Meet DA14's little brother? new [Re: shawnhar]
      #5687302 - 02/18/13 04:52 PM

Interesting. Looks as if there may have been another one off the Florida coast.

http://www.miamiherald.com/2013/02/17/3240318/ball-of-light-flashes-over-sout...


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Ravenous
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Re: Meet DA14's little brother? new [Re: Qwickdraw]
      #5688459 - 02/19/13 08:31 AM

Quote:

I may not understand the whole concept but do know that given the correct mass, speed and altitude of an object you can have it swing all the way around a planet and leave orbit again, ala Apollo 13 or any number of other examples.



Actually you are right in theory - has anybody mentioned aerobraking yet? (The technique Apollo used very accurately to save a vast amount of fuel.) The smaller meteor could have barely skimmed the atmosphere hours or days before, in some uninhabited location, going straight through but at a lower speed. With enough speed lost, it could have been recaptured before re-entering.

That probably didn't happen though, as (a) it's fantastically unlikely (b) the deceleration in the first pass would probably have shattered it, in the way that was seen on the day and (c) if the speed observed over Russia is over a certain value it was never in a captured orbit anyway. (I don't think any of it happened, I'm just mentioning this to see if I can start an internet myth!)

Quote:

That said, it is not hard to imagine that you can also have it approach from one hemisphere and fail to have enough escape velocity or mass and impact on the opposite hemisphere from its origin.




There's another idea - we (well NASA) frequently use close passes to boost the speed of a probe - the "slingshot". I wonder what geometry would be needed to cause the reverse and reduce speed, and IF it's practical. (Planets have captured moons on occasion.) Though it might not work on something on DA14's path as it's far out of plane...?


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Jarad
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Re: Meet DA14's little brother? new [Re: Ravenous]
      #5688472 - 02/19/13 08:41 AM

Quote:

There's another idea - we (well NASA) frequently use close passes to boost the speed of a probe - the "slingshot". I wonder what geometry would be needed to cause the reverse and reduce speed, and IF it's practical. (Planets have captured moons on occasion.) Though it might not work on something on DA14's path as it's far out of plane...?




This one is easy - to gain velocity via slingshot, you have your probe approach the planet from ahead of it in it's orbit. It swings in close and goes back out at the nearly same speed relative to the planet, but since it came from ahead of the planet it can gain up to 2x the planet's orbital velocity. In the simplest scenario, the probe is sitting still as the planet approaches at orbital velocity, it slingshots around the planet and ends up moving ahead of the planet by the same velocity (at orbital velocity relative to the planet, so now at 2x orbital velocity relative to the sun).

To lose speed, you have it approach from behind the planet in its orbit. Again, in the simplest form the probe comes up from behind at 2x the orbital velocity, for a relative velocity equal to orbital velocity. It swings around and leaves at orbital velocity relative to the planet, but now is sitting still relative to the sun.

Jarad


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Jason H.
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Re: Meet DA14's little brother? new [Re: Scott Horstman]
      #5688828 - 02/19/13 12:40 PM

Quote:

Interesting. Looks as if there may have been another one off the Florida coast.

http://www.miamiherald.com/2013/02/17/3240318/ball-of-light-flashes-over-sout...




Cuban meteor video
"Cosmic coincidence: Watch a SECOND meteor in the sky 6,000 miles from Russian space rock crash"

http://www.mirror.co.uk/news/weird-news/second-meteor-video-cuba-two-1712957#...

"Cuba, too, reports powerful meteorite explosion"

http://www.sfgate.com/news/science/article/Cuba-too-reports-powerful-meteorit...

The other coincidence is, Cienfuegos means 100 fires .

Jason W. Higley


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Glassthrower
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Re: Meet DA14's little brother? new [Re: Jason H.]
      #5688852 - 02/19/13 12:53 PM

Last thing I heard, the Cuba fireball was the real deal and was a good candidate to drop meteorites. But, Cuba is not a friendly environment for meteorite hunting.....for a variety of reasons, both political and logistical.

Ditto for a recent fireball seen over southern Florida, but that one plotted to drop it's payload (if any) over the ocean.

The Cuban meteorites (if any) may also be sitting at the bottom of the sea.


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Scott Horstman
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Re: Meet DA14's little brother? new [Re: Glassthrower]
      #5689157 - 02/19/13 04:00 PM

Here's a question for you guys.

Why would you suppose the Russian, San Fran and Cuban meteors all were more or less "grazers", coming in on a very shallow angle rather than coming in straight down?
Earth is nearly an 8000 mile target. Why would they so commonly graze the edge?


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Jarad
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Re: Meet DA14's little brother? new [Re: Scott Horstman]
      #5689233 - 02/19/13 04:34 PM

I don't think we are assuming that. Grazing came up as one way to try allow an object coming from the south to hit in the north (i.e. a first grazing pass to lose velocity, allowing it to swing around on the second pass). But it was presented as an extremely unlikely scenario, not what we actually think happened.

For actual impacts, if we assume the incoming trajectory is essentially random, the odds are slightly higher for lower angles of entry than higher angles. Look at the earth as a target, coming in straight down is the bullseye. The rings going out are progressively shallower entry angles, since the earth is a sphere not a flat circle. There is more cross-sectional area in the outer rings than the inner ones, so most hits will be at 45 degrees or less. Only bullseyes will come in at 90 degrees. But there will be a distribution of all entry angles, just more frequent for lower angles.

Jarad


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Scott Horstman
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Re: Meet DA14's little brother? new [Re: Jarad]
      #5689442 - 02/19/13 06:29 PM

Good point Jarad, I didn't look at it like that. It makes sense that probably 2/3 of meteors have a chance of entering at less than 45 degrees.

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Glassthrower
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Re: Meet DA14's little brother? new [Re: Jarad]
      #5689459 - 02/19/13 06:40 PM

FWIW, for those who are having fun recreating this event using impact simulators, consider this single statistic - in the 21st century, we have only one known iron meteorite that was recovered - the Kavarpura anomalous iron meteorite that fell over Rajasthan India on August 29, 2006.

In comparison, stony meteorites (chondritic and achondritic) have accounted for 85 recovered falls.

In a little over 13 years, we have had 86 total known meteorite falls. Only one of which was an iron.

The Kavarpura iron meteorite was a single recovered mass of less than 7 kilograms and didn't cause any destruction. I do not know it's size before it entered the atmosphere, went through the process of ablation, and then hit the ground as a grapefruit-sized, regmaglypted mass. The only possible sign of it's fall may have been a tiny dent or impact pit in the target ground that would not qualify to be called a "crater".

The term "city killer" comes into play with BIG iron bodies that come in just the right way and do not explode high in the atmosphere.

As was said earlier by someone else, a stony meteorite often does not survive the stresses atmospheric entry and they disrupt or explode much sooner and farther from the ground - producing an impressive visual display and one heck of a shockwave, but little relative damage on the ground.

This is what happened with the Chebarkul event - the angle of entry, speed of entry, the size of the body, and the composition of the body resulted in a cosmic starter pistol shot. It was loud, it got everyone's attention, but it was harmless in the grand scheme of potential impactors. Or to use the more popular analogy - this was a shot across our bow.

Play with the numbers in the simulator a little bit and you get a much deadlier result from a similar sized body of a different composition that enters our atmosphere at a higher velocity and at a more extreme/vertical angle.

This Russian meteorite could have been a Canyon Diablo crater-maker. Or Chicxulub. We should be able to detect the "planet killers" at a greater distance, but the so-called "city killers" can be frightfully small and hard to detect before it's too late. We need improvements in our detection systems.

We've had 86 warnings in the last 13+ years. This was the biggest and most damaging one since Tunguska, and we would be wise to continue improving our monitoring systems and perhaps accelerate the pace of that improvement. It's not being paranoid, it's being prudent.

Best regards and clear dark (and safer) skies,

MikeG


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llanitedave
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Re: Meet DA14's little brother? new [Re: Jarad]
      #5690059 - 02/20/13 12:48 AM

Quote:

Quote:

There's another idea - we (well NASA) frequently use close passes to boost the speed of a probe - the "slingshot". I wonder what geometry would be needed to cause the reverse and reduce speed, and IF it's practical. (Planets have captured moons on occasion.) Though it might not work on something on DA14's path as it's far out of plane...?




This one is easy - to gain velocity via slingshot, you have your probe approach the planet from ahead of it in it's orbit. It swings in close and goes back out at the nearly same speed relative to the planet, but since it came from ahead of the planet it can gain up to 2x the planet's orbital velocity. In the simplest scenario, the probe is sitting still as the planet approaches at orbital velocity, it slingshots around the planet and ends up moving ahead of the planet by the same velocity (at orbital velocity relative to the planet, so now at 2x orbital velocity relative to the sun).

To lose speed, you have it approach from behind the planet in its orbit. Again, in the simplest form the probe comes up from behind at 2x the orbital velocity, for a relative velocity equal to orbital velocity. It swings around and leaves at orbital velocity relative to the planet, but now is sitting still relative to the sun.

Jarad




I think that's backwards, Jarad. Every diagram I've ever seen, and every gravitational simulation I've done, increases the passing body's energy when it approaches from behind the orbital path of the larger planet. Here's a typical example.

The trick is that the probe (or asteroid) are both going in the same direction relative to the Sun, the larger planet pulling the small trailing probe towards it means that the probe gains much more velocity in the direction of its orbit around the Sun than the planet loses. If it passes in front of the planet, it's pulled back in velocity relative to the Sun.

The best way for it to be captured is for its perihelion to be just inside the orbit of the planet, so it's at the slow point of its velocity just as the planet catches up. There are other ways, but they involve more complex motions and often multiple encounters.

Of course, if the probe is in a retrograde orbit, that's a whole 'nother issue.


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Jarad
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Re: Meet DA14's little brother? new [Re: llanitedave]
      #5690290 - 02/20/13 07:35 AM

Quote:


I think that's backwards, Jarad. Every diagram I've ever seen, and every gravitational simulation I've done, increases the passing body's energy when it approaches from behind the orbital path of the larger planet. Here's a typical example.




We are saying the same thing, just mis-communicating about reference frames. The probe leaves going in roughly the opposite direction it approached from, relative to the planet. To gain speed, it comes in from in front of the planet, swings around behind it, and leaves going out ahead of it again. The closest point where it swings around is on the opposite side that it approached from.

For the slingshot boost scenario, they will usually both be going in the same direction relative to the sun, but the probe is going slower at first (so in the planet's reference frame, it is coming towards the planet from in front of it in orbit). After the swing, they are both going in the same direction, but the probe has picked up speed (in the planet's frame, the probe did a U-turn around the planet and is now headed in the opposite direction it started in).

Of course, that's the most extreme example. In reality, it will be a hyperbola, not a perfect U. More of a V with a curved bottom. If the open end of the V points forward in the planet's orbit, then the probe gains speed. If the open end points backward, it loses speed. By angling the V relative to the orbit, you can also change direction as well as speed (and of course in orbital mechanics changing speed cause a change in direction anyway...).

It only looks like a U in the planet's reference frame. From the sun's reference frame (how the diagram in the link is drawn) it looks much wider, since both objects are moving forward while the probe swings around the planet.

Jarad

Edited by Jarad (02/20/13 03:52 PM)


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Glassthrower
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Re: Meet DA14's little brother? new [Re: Jarad]
      #5690483 - 02/20/13 09:43 AM

Jarad, Dave, and others :

I am glad you guys are here for the parts of this that make my head explode. I can imagine the details once you fine gentlemen explain the mathematics and dynamics at work. I am completely right-brained and have little grasp of numbers. Without the explanations you offer here, I'd just be imagining rocks hitting a windshield with little understanding of how.

Just wanted to say thanks for that.

Best regards,

MikeG


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Dave Mitsky
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Re: Meet DA14's little brother? new [Re: Glassthrower]
      #5691161 - 02/20/13 03:33 PM

Regmaglypted, now there's a word that you don't see everyday.

http://www.answers.com/topic/regmaglypt

Dave Mitsky


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llanitedave
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Re: Meet DA14's little brother? new [Re: Jarad]
      #5691833 - 02/20/13 10:02 PM

Quote:

Quote:


I think that's backwards, Jarad. Every diagram I've ever seen, and every gravitational simulation I've done, increases the passing body's energy when it approaches from behind the orbital path of the larger planet. Here's a typical example.




We are saying the same thing, just mis-communicating about reference frames. The probe leaves going in roughly the opposite direction it approached from, relative to the planet. To gain speed, it comes in from in front of the planet, swings around behind it, and leaves going out ahead of it again. The closest point where it swings around is on the opposite side that it approached from.

For the slingshot boost scenario, they will usually both be going in the same direction relative to the sun, but the probe is going slower at first (so in the planet's reference frame, it is coming towards the planet from in front of it in orbit). After the swing, they are both going in the same direction, but the probe has picked up speed (in the planet's frame, the probe did a U-turn around the planet and is now headed in the opposite direction it started in).

Of course, that's the most extreme example. In reality, it will be a hyperbola, not a perfect U. More of a V with a curved bottom. If the open end of the V points forward in the planet's orbit, then the probe gains speed. If the open end points backward, it loses speed. By angling the V relative to the orbit, you can also change direction as well as speed (and of course in orbital mechanics changing speed cause a change in direction anyway...).

It only looks like a U in the planet's reference frame. From the sun's reference frame (how the diagram in the link is drawn) it looks much wider, since both objects are moving forward while the probe swings around the planet.

Jarad




Ok, I was looking at a Sun-centered frame of reference, and you were looking at the planet-centered one. I guess the critical item is that the closest approach (if we're looking for a slingshot effect, anyway) must occur on the trailing side of the planet relative to its orbit around the Sun.

It can get a bit more complicated, because a fast-moving object can overtake the planet from the trailing side and, under certain conditions, be boosted still further, as long as the overtaking direction is still oblique relative to the Sun. That would be a case where the planet-centered perspective would not see the object approaching from the forward side, but would still see it departing that way.


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llanitedave
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Re: Meet DA14's little brother? new [Re: Glassthrower]
      #5691857 - 02/20/13 10:17 PM

Quote:

Jarad, Dave, and others :

I am glad you guys are here for the parts of this that make my head explode. I can imagine the details once you fine gentlemen explain the mathematics and dynamics at work. I am completely right-brained and have little grasp of numbers. Without the explanations you offer here, I'd just be imagining rocks hitting a windshield with little understanding of how.

Just wanted to say thanks for that.

Best regards,

MikeG




You can do this at home. And you don't have to be a math genius.

Years ago I used the code on this web site to construct a toy gravitational simulator in javascript.

It's "toy" in that it's relatively slow and that it only handles a few bodies at a time, but the calculations are rigorous and the gravitational interactions are correct. All I had to do was change the code from C to javascript and adapt it to a GUI for my browser.

I spent hours playing with different setups and watching it run. OK, a "normal" person might have found that kind of project tedious, but I was spending 3 hours a day on a bus commute and tedium was unavoidable. Anyway, you watch these kinds of things happen long enough, and the visualization starts to become intuitive.

And your friends start questioning your sanity.


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Glassthrower
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Re: Meet DA14's little brother? new [Re: llanitedave]
      #5699421 - 02/25/13 08:45 AM

Chebarkul-Chelyabinsk is an Apollo!

http://www.technologyreview.com/view/511691/astronomers-calculate-orbit-of-ch...

More accurate numbers have come in since this article was written, and an updated orbit is being calculated now.


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Glassthrower
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Re: Meet DA14's little brother? [Re: Glassthrower]
      #5699888 - 02/25/13 01:53 PM

Interestingly, DA14's recent pass altered it's orbit sufficiently that it has been reclassified as an Aten class object, instead of an Apollo.

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