Explanation: The Peekskill meteor of 1992 was captured on 16 independent videos and then struck a car. Documented as brighter than the full Moon, the spectacular fireball crossed parts of several USA states during its 40 seconds of glory before landing in Peekskill, New York. A video of the fireball beyond a high school football game in Johnstown, Pennsylvania, USA, is pictured above. The resulting meteorite is imaged here, and was found to be composed of dense rock and has the size and mass of an extremely heavy bowling ball. If you are lucky enough to find a meteorite just after impact, do not pick it up -- parts of it are likely to be either very hot or very cold. Tracking meteors origins and destinations might be easier in this modern digital age, but many security cameras videos that likely caught a bright fireball are not preserved. If you would like to volunteer to help meteor science by locating images and videos of newly occurring fireballs within 48 hours after they occur, here is a place to sign up.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 5:45 am
by Chris Peterson
It is a myth that you should not pick up a freshly fallen meteorite. Such an object is extremely unlikely to be either so hot or so cold that it could be unsafe. In fact, if you should have a meteor land in front of you, I would strongly advise you to feel it and try to objectively assess its temperature, as that can be very valuable information in analyzing details of the fall. It only takes a few minutes for that temperature information to be lost forever.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 12:57 pm
by NoelC
And don't forget that picking it up before someone else does could be very healthy for your wallet.
-Noel
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 1:09 pm
by Redbone
I saw this meteorite. I was driving northwest on New Hampshire Avenue in Cloverly, following my buddy who was driving a van. It was partly cloudy and at first I thought it was lightning but the flash continued and I could see it burning through the clouds, spectacular. When I looked back at the road, the van had stopped and I almost ran into him. When we got back to my friend's house, I told my story and his wife said yeah, yeah. Next day she went to work at USDA and called me up. Everything matched up, time and direction, a meteorite had hit a parked car in New York.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 1:42 pm
by RJN
Chris Peterson wrote:It is a myth that you should not pick up a freshly fallen meteorite. Such an object is extremely unlikely to be either so hot or so cold that it could be unsafe. In fact, if you should have a meteor land in front of you, I would strongly advise you to feel it and try to objectively assess its temperature, as that can be very valuable information in analyzing details of the fall. It only takes a few minutes for that temperature information to be lost forever.
Chris,
I wrote that line based on this unusual daydream I have that I am opening my car door when I suddenly see a meteor land across the parking lot, roll right up to me, which I stop it with my shoe. I then have the dilemma as to whether to pick it up or not. So I have been keeping tabs on this over the last few years. What should I do?
My first inclination is to not pick it up because it would be too hot. But I asked a close acquaintance about this a few years ago who has some experience with meteors (Brad Schaefer now at LSU) and he pointed out to to me that might well be cold. The hotness might come from the outside heating in the Earth's atmosphere, while the inside might remain nearly as cold as it was when drifting through space. How much has ablated from the now meteorite during the later part of its fall might well determine its outer temperature.
So I wrote that line drawing on the memory of that conversation. I have also followed several links on the topic I have chanced across since then. Googling the topic again now, here are two:
So it may be that the skin temperature of just fallen meteorites is not actually known from first hand experience. If anyone can find links to first person stories that would be interesting. I would now bet that the size and composition of meteorites might be important, and that some pockets might be hot, some cold, depending on their composition and exposure during fall. I don't see how the meteorite could know the ambient temperature, though, having just fallen moments before, although some materials could equilibrate quickly.
So back to my strange daydream -- should I pick up the meteorite? I am still unsure. Perhaps I should almost follow your suggestion, but rather hover my hand over various parts of the meteorite and make careful notes which parts seem to be hot or cold. The rest of my life could then be spent trying to get people to believe the result.
- RJN
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 2:52 pm
by zloq
So they could be very hot or they could be very cold - and there is a lack of data to know for sure. I'm not sure how that would translate to being certain they are safe to touch on arrival, so caution seems prudent.
This reminds me of Letterman's report on the fight over the remains of baseball legend Ted Williams. One side of the family wanted them cremated while the other requested cryogenic storage. The judge finally compromised on: lukewarm.
The mean of the expected extremes may not have good predictive value if there is a lack of experimental data and the standard deviation is huge.
zloq
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 3:04 pm
by neufer
RJN wrote:
Chris Peterson wrote:
It is a myth that you should not pick up a freshly fallen meteorite. Such an object is extremely unlikely to be either so hot or so cold that it could be unsafe. In fact, if you should have a meteor land in front of you, I would strongly advise you to feel it and try to objectively assess its temperature, as that can be very valuable information in analyzing details of the fall. It only takes a few minutes for that temperature information to be lost forever.
I wrote that line based on this unusual daydream I have that I am opening my car door when I suddenly see a meteor land across the parking lot, roll right up to me, which I stop it with my shoe. I then have the dilemma as to whether to pick it up or not. So I have been keeping tabs on this over the last few years. What should I do?
My first inclination is to not pick it up because it would be too hot. But I asked a close acquaintance about this a few years ago who has some experience with meteors (Brad Schaefer now at LSU) and he pointed out to to me that might well be cold. The hotness might come from the outside heating in the Earth's atmosphere, while the inside might remain nearly as cold as it was when drifting through space. How much has ablated from the now meteorite during the later part of its fall might well determine its outer temperature.
Hmmm...where is Sigmund Freud when we need really him
I don't know the answer to this but would tend to agree with Chris:
1) A dark meteorite in space should have a solar heated equilibrium temperature of about 250K ...not all that cold.
2) Ablation should keep the meteorite from getting overly hot.
3) Passing through many miles of troposphere should be very effective at bringing the meteorite to ambient temperature.
4) The Peekskill car doesn't look at all singed.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 5:39 pm
by Chris Peterson
RJN wrote:So back to my strange daydream -- should I pick up the meteorite? I am still unsure. Perhaps I should almost follow your suggestion, but rather hover my hand over various parts of the meteorite and make careful notes which parts seem to be hot or cold. The rest of my life could then be spent trying to get people to believe the result.
The question of meteorite temperature is very amenable to analysis, and the theoretical results are consistent with the limited observational evidence.
The analyses you found both start with an erroneous assumption, that space is cold. In reality, space has no temperature. (Strictly, temperature is a measure of the average kinetic energy of the particles making up a medium. In the inner Solar System, the "temperature of space" is a few thousand K, but the particle density is so low that virtually no energy is transferred convectively.) The temperature of an object in space is determined by radiative physics: the Stephan-Boltzmann Law and Kirchoff's Law of Radiative Equilibrium. A meteorite is produced by a body with a nominal diameter of 1 meter, which has spent somewhere between days and years in orbit at about 1 AU. When you use the above equations, along with reasonable values for absorptivity and emissivity for asteroidal materials, you can come up with a range of meteoroid temperatures. These range from about -10°C for chondrites to +90° for iron.
When the body enters the atmosphere, its outer surface will heat to several thousands of degrees (the choice of units isn't really important here). But that heating phase typically only lasts a few seconds, and virtually all the heat is removed by ablation. So it is unlikely that the interior of the meteorite experiences any significant heating at all.
Once the hypersonic ablation phase finishes, the surviving material goes into dark flight. It will fall at about 100 meters/second for several minutes in air at -60°C to -40°C. This forced convective heat transfer is very efficient, so we expect the meteorite to undergo rapid cooling, from the outside inward. The last minute or so of the fall will be through air near surface ambient, so in most cases this will contribute a bit of rewarming at the surface of the meteorite.
There are several dozen reports of people picking up freshly fallen meteorites. No injuries have ever been documented, but reports range from hot to cold. It is suggested that in many cases where the stone is reported as hot, it is actually at or below ambient, and therefore will be cold to the touch. People frequently confuse the sensations of hot and cold, particularly if there is an expectation in advance as to temperature.
There are several reports of frost on the interior of meteorites that split open on impact; I've not heard of frost being observed on the exterior of freshly fallen meteorites.
So if you are lucky enough to have a meteorite fall at your feet, test the temperature. I'd do as you suggest- put my hand near it and start by touching it gingerly. But I'd not do that out of any real concern for hurting myself, but because it seems like the best way to accurately evaluate the object's temperature.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 6:58 pm
by RJN
Chris Peterson wrote:When you use the above equations, along with reasonable values for absorptivity and emissivity for asteroidal materials, you can come up with a range of meteoroid temperatures. These range from about -10°C for chondrites to +90° for iron.
That is really interesting! I was not aware of literature on the subject. Can you post a reference or two? It makes sense because a perfectly thermally conducting and radiating blackbody at the distance from the Sun as the Earth would have, nearly, the average temperature of the Earth. So I guess the devil is in the details -- the amount of thermal conduction, the meteor radiation and other cooling abilities, and its thermal history. If it came from near a close passage near the Sun and had the right thermal conductivity, it may well be hot. More likely, though, it came from a location further from the Earth from the Sun where the space temperature (read: the temperature of a perfectly non-reflecting, perfectly thermally conducting and radiating blackbody) would be relatively cold.
Chris Peterson wrote:
So if you are lucky enough to have a meteorite fall at your feet, test the temperature. I'd do as you suggest- put my hand near it and start by touching it gingerly. But I'd not do that out of any real concern for hurting myself, but because it seems like the best way to accurately evaluate the object's temperature.
This reminds me of a story I was once told by a former professor here at Michigan Tech (since gone to U. Hawaii). When he was little in New York City, he tried to impress his mom saying that he could ground a finger on his hand and then touch the third rail on the subway with another finger on the same hand, and then release it, without getting electrocuted. So his mom thought about it for a bit and then said "OK, try it". But as sure as he was, he couldn't bring himself to do it. This scenario comes up in other contexts in my life at times and could be called the "Ftaclas Effect". So although touching something very hot or very cold would not be as life threatening as improperly touching a subway third rail, indeed the Ftaclas Effect would probably keep me from touching a fresh meteorite immediately.
- RJN
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 7:46 pm
by skyhound
I agree with Chris (for once) that there is every reason to expect meteorites to be at ambient temperature when they hit the ground. As far as touching it goes, it is my understanding that the scientific value of many "just arrived" meteorites is higher if they have not been handled. What I'd do if I saw one of these is to not touch it, but to get a camera and document in in situ. I would mark the exact position of the fall so that I could find it again. Then I would gently place it into a ziplock bag (assuming it would fit!) using tongs or rubber gloves, taking care to handle it as little as possible. Then I'd contact several meteoriticists to gauge their interest in studying it and submit it to one of them for study. I would grant them a slice of the meteorite in return for a scientific classification. Finally I'd decide whether or not I wanted to keep it, sell it (possibly for a substantial amount of money) or donate it to a museum.
Greg
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 8:00 pm
by neufer
[img3="RJN: Are you kidding? Stick my tongue to that meteorite? That's dumb!
Peterson: That's 'cause you know it'll stick!
RJN: You're full of it!
Peterson: Oh yeah?
RJN: Yeah!
Peterson: Well I double-DOG-dare ya!
(NOW it was serious. A double-dog-dare. What else was there but a "triple dare you"? And then, the coup de grace of all dares, the sinister triple-dog-dare.)
Chris Peterson wrote:
So if you are lucky enough to have a meteorite fall at your feet, test the temperature. I'd do as you suggest- put my hand near it and start by touching it gingerly. But I'd not do that out of any real concern for hurting myself, but because it seems like the best way to accurately evaluate the object's temperature.
This reminds me of a story I was once told by a former professor here at Michigan Tech (since gone to U. Hawaii). When he was little in New York City, he tried to impress his mom saying that he could ground a finger on his hand and then touch the third rail on the subway with another finger on the same hand, and then release it, without getting electrocuted. So his mom thought about it for a bit and then said "OK, try it". But as sure as he was, he couldn't bring himself to do it. This scenario comes up in other contexts in my life at times and could be called the "Ftaclas Effect". So although touching something very hot or very cold would not be as life threatening as improperly touching a subway third rail, indeed the Ftaclas Effect would probably keep me from touching a fresh meteorite immediately.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 9:30 pm
by orin stepanek
If I found a meteorite; I would more than likely think it was a stone or rock and pass it by. Unless of course; I saw it fall out of the sky. From looking at the damage to the car; I'd say it packs quite a wallop when it hits and hope I never get hit by one.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Sun Jan 23, 2011 11:54 pm
by nstahl
I was going to suggest spitting on the subject meteorite to see if steam or ice resulted but I guess that would reduce the scientific value. But it would resolve this scientific question.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 1:00 am
by starswarm magellan
New York can't catch a break.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 1:03 am
by Chris Peterson
orin stepanek wrote:If I found a meteorite; I would more than likely think it was a stone or rock and pass it by. :? Unless of course; I saw it fall out of the sky. 8-) From looking at the damage to the car; I'd say it packs quite a wallop when it hits and hope I never get hit by one.
Meteorites are classified as finds, meaning you just came upon them, and falls, meaning they were witnessed, either in the fireball stage or actually seen hitting the ground. It turns out falls are much more common than you'd expect (at least, more common than I'd expect), although finds still account for the vast majority of meteorites.
Getting hit by a meteorite is like getting hit by a rock of the same size tossed off a building a few stories high. Not comfortable, I'm sure!
SylacaugaHulittHodgesW.jpg (9.69 KiB) Viewed 3932 times
Mrs Hulitt Hodges of Sylacauga, Alabama, who was struck by a 4 kg meteorite that came through the roof of her house on 30 March 1954.
Betulia Toro & Mrs. E. Hulitt Hodges of Sylacauga
Posted: Mon Jan 24, 2011 4:25 am
by neufer
Chris Peterson wrote:
Mrs Hulitt Hodges of Sylacauga, Alabama, who was struck by a 4 kg meteorite that came through the roof of her house on 30 March 1954.
http://en.wikipedia.org/wiki/Hodges_Meteorite wrote:
<<The Sylacauga meteorite fell on November 30, 1954 at 2:46pm near the town of Sylacauga, Alabama. The meteor made a fireball visible from three states as it streaked through the atmosphere, even though it fell early in the afternoon. Although officially known as the Sylacauga meteorite, it is often referred to as the Hodges meteorite because a fragment of it struck Ann Elizabeth Hodges (1923–1972).
The Sylacauga meteorite is the first documented extraterrestrial object to have injured a human being. The grapefruit-sized fragment crashed through the roof of a frame house in Oak Grove, Alabama, bounced off a large wooden console radio, and hit Hodges while she napped on a couch. The 31-year-old woman was badly bruised on one side of her body but able to walk. The event received worldwide publicity.
The Sylacauga meteorite is not the only extraterrestrial object to have struck a human. In 1992 a very small fragment (3g) of Mbale meteorite hit a young Ugandan boy, but it had been slowed down by a tree and did not cause any injury.
The United States Air Force sent a helicopter to take the meteorite. Eugene Hodges, the husband of the woman who was struck, hired a lawyer to get it back. The Hodges' landlord, Bertie Guy, also claimed it, wanting to sell it to cover the damage to the house. There were offers of up to $5,000 for the meteorite. By the time it was returned to the Hodgeses, over a year later, public attention had diminished and they were unable to find a buyer willing to pay.
Ann Hodges was uncomfortable with the public attention and the stress of the dispute over ownership of the meteorite. Against her husband's wishes, she donated it to the Alabama Museum of Natural History where it is displayed at the University of Alabama in Tuscaloosa.
The Sylacauga meteorite is classified as an ordinary chondrite of H4 group. The meteoroid came in on the sunward side of the Earth, so when it hit our planet it had passed the perihelion and was traveling outward from the Sun. Considering the orbit estimations, the best candidate as parent body is 1685 Toro.>>
http://en.wikipedia.org/wiki/1685_Toro wrote:
<<1685 Toro is an Apollo asteroid. It orbits the Sun in an 8:5 resonance with Earth, and a 13:5 resonance with Venus; as a result, it is sometimes called "Earth's second satellite". Toro was discovered by Carl A. Wirtanen at the Lick Observatory in 1948. It was the third Apollo asteroid to be discovered. The name honours Betulia Toro, wife of the astronomer Samuel Herrick. Herrick had studied the asteroid's orbit, and requested the name, along with that of 1580 Betulia.>>
* Jim Nabors (born June 12, 1930), actor and singer, star of Gomer Pyle, U.S.M.C. and The Andy Griffith Show. For 25 years, Nabors owned a macadamia nut plantation on Maui before selling it to the National Tropical Botanical Gardens, a conservationist organization. Macadamias are toxic to dogs. Ingestion may result in macadamia nut toxicosis, which is marked by weakness with the inability to stand within 12 hours of ingestion. Recovery is usually within 24 hours.
Click to play embedded YouTube video.
Click to play embedded YouTube video.
* Van Allen Plexico (born January 12, 1968) is an American professor of Political Science and History and a science fiction and fantasy author.
Plexico has lectured, written, and spoken professionally on space science, alternate history, and the historical roots of contemporary comic books and science fiction and fantasy literature. He has been published in print and online in the areas of book, television, film, and comics criticism and commentary, and has moderated discussion panels and emceed trivia tournaments at science fiction conventions around the US, beginning in 1998.>>
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 6:20 am
by Chris Peterson
RJN wrote:
Chris Peterson wrote:When you use the above equations, along with reasonable values for absorptivity and emissivity for asteroidal materials, you can come up with a range of meteoroid temperatures. These range from about -10°C for chondrites to +90° for iron.
That is really interesting! I was not aware of literature on the subject. Can you post a reference or two?
I've never really seen anything formal. I've done the calculations, and I've seen others do them as well. It's one of those things that comes up from time to time.
It makes sense because a perfectly thermally conducting and radiating blackbody at the distance from the Sun as the Earth would have, nearly, the average temperature of the Earth.
Right. The temperature range on Earth is moderated a bit because of convective heat transfer, but a rock sitting in the Sun is a rock sitting in the Sun, whether it's on the side of a hill or out in space, 1 AU from the Sun.
So I guess the devil is in the details -- the amount of thermal conduction, the meteor radiation and other cooling abilities, and its thermal history. If it came from near a close passage near the Sun and had the right thermal conductivity, it may well be hot. More likely, though, it came from a location further from the Earth from the Sun where the space temperature (read: the temperature of a perfectly non-reflecting, perfectly thermally conducting and radiating blackbody) would be relatively cold.
Virtually every sporadic meteor I've recovered an orbit for was in a moderately eccentric orbit, with aphelion in the asteroid belt and perihelion not much less than 1 AU. In such an orbit, the meteoroid will spend many days near 1 AU from the Sun, so it will be near thermal equilibrium and its previous history won't matter (assuming it is on the order of a meter in size; if it is many meters it might never reach equilibrium). As far as details, there are some others I didn't discuss. The body could be very far from spherical, and it could be rotating particularly slowly. During its meteor phase, it could be oriented and in a very shallow trajectory, allowing more time for heating. Or, it could be oriented and mechanically stable, surviving much lower than most before slowing down, reducing the time it has to cool. My earlier discussion of meteorite temperatures really only applies to "typical" meteorites, which probably account for most. But there are reports of meteorites that seem to be highly atypical.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 2:21 pm
by WildGuruLarry
I think if I saw a meteorite land, I would think "when am I ever going to be able to be potentially burnt/frozen by an object from outer space again"? And then I would touch the darn thing and expand my knowledge.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 4:12 pm
by neufer
WildGuruLarry wrote:
I think if I saw a meteorite land, I would think
"when am I ever going to be able to be potentially burnt/frozen by an object from outer space again"?
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 6:09 pm
by zloq
Chris Peterson wrote:
I've never really seen anything formal. I've done the calculations, and I've seen others do them as well. It's one of those things that comes up from time to time.
There are quite a few papers on the temperature of meteoroids in space.
Wylie in 1934 confronts the notion that meteors are fireballs - hence meteorites should be hot. He cites reports that stone meteorites were cold to the touch, or barely warm - but he acknowledges some stone and iron meteorites were reported as warm or hot. He states the expected temperature of a meteoroid in space as 39F.
Butler in the 1963 calculated the temperature of iron meteoroids at varying distances from the sun and concluded a rough value of 90C for one entering the earth's atmosphere. Later in 1966 he reported experimental measurements under simulated space conditions for various meteoroid materials. The focus of that paper was to determine the expected temperature of a meteoroid that approached the orbit of mercury, since if it is high enough to anneal the crystal structure, any meteoroid without this annealing would be unlikely to have come that close to the sun in its past.
Staley in 1966 has a more comprehensive paper on theoretical estimates of meteoroid temperature and specifically addresses the idea they could be cold. One subtlety is that during any period where the meteoroid is in the shadow of the earth, it will be cooling due to radiative loss not balanced by absorption from the sun. Another subtlety is that for large objects that are headed toward the sun from a distant origin, they may be traveling fast enough that they are not in thermal equilibrium with the sun and could have cold internal temperatures.
In 1998 Lyne reports on models of atmospheric entry of large meteors, applied to the Tunguska event. He points out in the abstract that 'The atmospheric entry of a meteor is quite complex..." This is quite different from saying it is all well understood and easily modeled.
In 2004 Popova reports on meteoroid ablation models. Like many papers, this focuses on small objects that don't reach the ground. Even so he points out the complexity of the models and their inadequacies, and the lack of observational data for validation.
I don't know of a detailed simulation of the entry of an object that results in, say, a 1-100 kg iron meteorite. I imagine it would be quite a task to simulate with any confidence.
As far as space being "cold" - there is an anthropomorphic view that temperature only has importance in terms of heat transfer by direct contact, while even for humans on earth, radiation plays a big role. Pre-1960's writings may say you need atoms in space in order to have temperature, but nowadays it's more common just to regard space as being bathed in cosmic background radiation that amounts to photon gas with a Maxwell-Boltzmann distribution corresponding to around 2.7K - which I consider cold. When it comes to a meteroid in space, it sees that 2.7K radiation in all directions except a tiny part of the sky containing the sun, which is at much higher temperature. The equilibrium temperature it reaches is due to the balance between its energy radiatively received from, and lost to, both the sun and the "coldness of space."
There are high velocity atoms and ions in the solar system, but they are not in equilibrium with the background radiation and would have minimal contribution to a meteoroid's temperature in comparison to the sun and background radiation.
I personally find it unlikely a freshly fallen meteorite would be cold, but I have no problem with the idea it might be quite hot, particularly if it is iron and especially if it fragmented explosively, or hit with high velocity.
zloq
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 6:46 pm
by neufer
zloq wrote:
I personally find it unlikely a freshly fallen meteorite would be cold, but I have no problem with the idea it might be quite hot, particularly if it is iron and especially if it fragmented explosively, or hit with high velocity.
Kinetic energy of a 1 kg meteorite at 90 m/s terminal velocity = 4,050 Joules.
Specific heat capacity of iron = 450 Joules/(kg.ºC)
If all of the kinetic energy went into heating up just the meteorite (and not into the ground, car, house, wooden console radio, Mrs. Hodges, couch, etc.) the meteorite would warm by just ~9ºC (= 4,050/450).
http://en.wikipedia.org/wiki/Terminal_velocity wrote:
<<Based on wind resistance, for example, the terminal velocity of a skydiver in a belly to earth free-fall position is about 55 m/s. In this example, a speed of 50% of terminal velocity is reached after only about 3 seconds, while it takes 8 seconds to reach 90%, 15 seconds to reach 99% and so on. Higher speeds can be attained if the skydiver pulls in his or her limbs. In this case, the terminal velocity increases to about 90 m/s, which is also the terminal velocity of the peregrine falcon diving down on its prey. And the same terminal velocity is reached for a typical .30-06 bullet travelling in the downward vertical direction — when it is returning to earth having been fired upwards, or perhaps just dropped from a tower — according to a 1920 U.S. Army Ordnance study.>>
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 10:34 pm
by zloq
neufer wrote:
Kinetic energy of a 1 kg meteorite at 90 m/s terminal velocity = 4,050 Joules.
You are assuming the object has reached its terminal velocity. If it explosively fragmented from a much larger, faster body say 1km above the ground, it would only shed part of its velocity from drag before hitting the earth, so its terminal velocity would be less important than whatever initial velocity it had at the time of fragmentation.
zloq
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 10:53 pm
by Chris Peterson
zloq wrote:You are assuming the object has reached its terminal velocity. If it explosively fragmented from a much larger, faster body say 1km above the ground, it would only shed part of its velocity from drag before hitting the earth, so its terminal velocity would be less important than whatever initial velocity it had at the time of fragmentation.
Meteorite impacts that occur while the body is still carrying some of its cosmic velocity are extremely rare (thankfully!) It is perfectly reasonable to consider all meteorites to be falling at terminal velocity, unless we are specifically talking about rare cratering events.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Mon Jan 24, 2011 10:59 pm
by neufer
zloq wrote:
neufer wrote:
Kinetic energy of a 1 kg meteorite at 90 m/s terminal velocity = 4,050 Joules.
You are assuming the object has reached its terminal velocity. If it explosively fragmented from a much larger, faster body say 1km above the ground, it would only shed part of its velocity from drag before hitting the earth, so its terminal velocity would be less important than whatever initial velocity it had at the time of fragmentation.
If it was going to explode it would be more likely to do it at 50 km above the ground or higher.
If it makes it intact to the troposphere it will probably stay intact.
Re: APOD: Peekskill Fireball Video: Johnstown (2011 Jan 23)
Posted: Tue Jan 25, 2011 1:42 am
by zloq
Chris Peterson wrote: It is perfectly reasonable to consider all meteorites to be falling at terminal velocity, unless we are specifically talking about rare cratering events.
I think it's important to distinguish simplified models of typical scenarios from what can actually happen in the complex situation of a large object fragmenting at high velocity so that a chunk slams to the earth for immediate inspection - with or without a crater. I don't consider this straightforward and easily modeled with confidence, and I see words to that effect in the literature cited above. Therefore I consider "terminal velocity" an assumption that could easily be false - and I give the specific example of a high speed, low altitude fragmentation event.
The main point of my earlier posting was to emphasize the extensive literature on these specific topics and to encourage people to cite actual research.