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Natural Science Forum / Biology / Paleontology / June 2007Ancient Meteor Blast May Have Caused Extinctions (Forwarded)
Hi, I found an interesting article from sci.astro. Please take a look for your comments. It is quite unbelievable that so big meteorite (mentioned below text) about 5 km in diameter had hit to the Earth about 13000 years ago and possible caused "nuclear winter" ??? Best Regards, Hannu Newsgroups: sci.astro Path:g2news1.google.com!news2.google.com! newsfeed.stanford.edu!elk.ncren.net!newsflash.concordia.ca!news.sfu.ca! utnut!utgpu! utinfo!crux.astro.utoronto.ca!ayee From: Andrew Yee <a...@crux.astro.utoronto.ca> Subject: Ancient Meteor Blast May Have Caused Extinctions (Forwarded) X-Nntp-Posting-Host: crux.astro.utoronto.ca Content-Type: TEXT/PLAIN; charset=US-ASCII Message-ID: <Pine.LNX. 4.30.0706071433190.19843-100000@crux.astro.utoronto.ca> Sender: n...@campus-news-reading.utoronto.ca Organization: UTCC Campus Access Mime-Version: 1.0 Date: Thu, 7 Jun 2007 18:33:44 GMT University of California-Santa Barbara CONTACT Gail Gallessich, 805-893-7220 FEATURED RESEARCHER Luann Becker, 206-465-1005 May 23, 2007 Ancient Meteor Blast May Have Caused Extinctions, Report UC Santa Barbara Scientists Santa Barbara, Calif. -- New scientific findings suggest that a large, extraterrestrial rock may have exploded over North America 13,000 years ago, explaining riddles that scientists have wrestled with for decades, including an abrupt cooling of the atmosphere and the extinction of large mammals. Two scientists from the University of California, Santa Barbara presented the discovery today, along with two other researchers at a news conference at the annual meeting of the American Geophysical Union being held in Acapulco, Mexico. Over 20 scientists contributed to the discovery. James Kennett, paleoceanographer and professor emeritus in the Department of Earth Science at UC Santa Barbara, said that the discovery potentially explains three of the most-debated controversies of recent decades. "This is what happens when you do interdisciplinary science," said Luann Becker, research scientist with UC Santa Barbara's Institute of Crustal Studies. "You can solve some of the bigger problems." The time period in question is called the "Younger Dryas," a time of abrupt cooling that lasted for about 1,000 years and occurred during an inter-glacial warm period. Evidence for the temperature change is recorded in ice cores. According to the scientists, the extraterrestrial rock must have been about five kilometers across, and either exploded in the atmosphere or directly hit the Laurentide ice sheet located in the Northeastern section of North America. Wildfires across the continent would have resulted from the fiery impact, killing off the vegetation that was the food supply of many of the larger mammals like the woolly mammoths, causing them to go extinct. Since the Clovis people of North America hunted the mammoths as a major source of their food, they too were affected by the impact and their culture died out, explained Becker. The scientific team visited over a dozen archaeological sites in North America where they found high concentrations of iridium, an element that is rare on Earth, and is almost exclusively associated with meteors. They found microspherules of glass-like carbon, which form at high temperatures and are thought to be a result of the impact blast. Also present were another type of impact tracer -- carbon molecules called fullerenes with gases trapped inside. The team concluded that the impact of the space rock melted a large portion of the Laurentide ice sheet, causing enormous amounts of cool, fresh water to flow into the Atlantic and Arctic Oceans. This would have caused a major disruption of the circulation of warm and cold water in these oceans, leading to a cooler atmosphere and the glaciation of the Younger Dryas period. The scientists found evidence for the impact as far west as the Santa Barbara Channel Islands. Kennett said that the best examples from the West Coast were found at a site on Santa Rosa Island. The Paleoclimate Program of the National Science Foundation and NASA funded this research. > Hi, > [quoted text clipped - 85 lines] > go > extinct. Problem: If it had struck an ice sheet that has been estimated to have been as much as 8,000-10,000 feet thick, what forests existed that could have caught fire? George > > Hi, > [quoted text clipped - 91 lines] > > George Yes, that is a problerm if meteorite is in question. What about possibility of icy comet of about 5 km in diameter ? Do any existing eveidences support this possibility ? Hannu >> > Hi, >> [quoted text clipped - 99 lines] > > Hannu Same problem. If it struck a 10,000 feet thick ice sheet, there are no forests to catch fire, or else get destroyed. On the other hand, the amount of moisture released into the atmopshere would be huge. George In sci.bio.paleontology George <george@yourservice.com> wrote: > Same problem. If it struck a 10,000 feet thick ice sheet, there are no > forests to catch fire, or else get destroyed. On the other hand, the > amount of moisture released into the atmopshere would be huge. I think the question related to the source of water being the comet rather than the ice sheet. Thus, the comet impacts forest and the meltwater from the comment cools and dilutes the northern currents.  SignatureThomas T. Veldhouse If you took all of the grains of sand in the world, and lined them up end to end in a row, you'd be working for the government! -- Mr. Interesting > In sci.bio.paleontology George <george@yourservice.com> wrote: >> [quoted text clipped - 7 lines] > from the > comment cools and dilutes the northern currents. Except that the suggestion was that it occurred up in Labrador, where there was a 10,000 feet thick ice sheet at the time. So there could hardly have been a forest to get destroyed at that location. That was the point I was making. George > > In sci.bio.paleontology George <geo...@yourservice.com> wrote: > [quoted text clipped - 21 lines] > > George Could this climate change in Younger Dryas period be caused also by solar variability, which could caused for example the break of Laurentian (?) ice-lake, if so then this meteorite/comet theory would not be needed ? I red in some Nature article that this climate change started possible in few tens of years lasted about 1000 years, and also ended few tens of years ? Could the cause of this cold Younger Dryas period be changes in sea currents ? One changed sea current could be the Golf-stream, which definitely would have influenced the climate conditions for example here in Finland ? Hannu >> > In sci.bio.paleontology George <geo...@yourservice.com> wrote: >> [quoted text clipped - 45 lines] > > Hannu Here is a link that discusses some of the ideas that have been bounced around for what caused it, and possibly other similar periods. http://en.wikipedia.org/wiki/Younger_Dryas George It's never been convincing to me that the early North American peoples were the sole force behind a rapid extinction holocaust that took out all the megafauna except the American bison. Native peoples in Africa had hundreds of thousands of years to multiply and to hunt game, where North Americans had only a couple of thousand, and yet Africa is (or was, until modern large-scale poaching and development) host to a very healthy collection of very large mammals and their predators. That there was an external cause like a comet assisting in the destruction seems to me (an admitted non-expert) to be more plausible. Matt Bille > >> > In sci.bio.paleontology George <geo...@yourservice.com> wrote: > >> [quoted text clipped - 52 lines] > > George > >> > In sci.bio.paleontology George <geo...@yourservice.com> wrote: > [quoted text clipped - 52 lines] > > George This is seems to be a good reference. You mention that there could also be similar periods. I took a quick look at the picture which was in your reference then I get following approximate similar periods: http://en.wikipedia.org/wiki/Younger_Dryas http://en.wikipedia.org/wiki/Image:Epica-vostok-grip-40kyr.png 37000-35500 years ago, 34500-33500 years ago, 33000-32000 years ago, 31500-28500 years ago, 28000-27000 years ago, 27000-14000 years ago, 13000-11500 years ago (approx. Younger Dryas period) Causes of these could be possible: solar variability/ice-lake/sea currents/possible comet or asteroid impacts ??? I must read your reference and references in it more closely. I remember that one possible origin of fractions of comets could be at least those comets which go too close to the Sun like the comet MacHoltz/P (if I remembered the name right ?) which could be fractioned due to too big gravitational forces near the Sun. Orbits of these fragments could then be expanding, maybe they are "collected" near the Jupiter or into the asteroid belt with Jupiter's pull force ??? Hannu > > "mathematician" <hapor...@luukku.com> wrote in message > [quoted text clipped - 90 lines] > > Hannu Sorry that I did not rember to mention also an impotant matter that on the million year time scale four periods of enhanced VOLCANIC ACTIVITY have been identified in deep-sea core records, of which two (in the middle Pliocene and middle Micoene epochs) coincided with the beginning of glaciation in different parts of the world. (ref: The Cambridge Encyclopedia of Earth Sciences, 1981, pages 297-310, page. 305). Hannu In sci.bio.paleontology George <george@yourservice.com> wrote: > Except that the suggestion was that it occurred up in Labrador, where there > was a 10,000 feet thick ice sheet at the time. So there could hardly have > been a forest to get destroyed at that location. That was the point I was > making. Not during an interstitial warming period, as was noted in the article. SignatureThomas T. Veldhouse Software is like sex; it's better when it's free. -- Linus Torvalds > In sci.bio.paleontology George <george@yourservice.com> wrote: >> [quoted text clipped - 7 lines] > > Not during an interstitial warming period, as was noted in the article. From the artricle: "According to the scientists, the extraterrestrial rock must have been about five kilometers across, and either exploded in the atmosphere or directly hit the Laurentide ice sheet located in the Northeastern section of North America." So if it hit the ice sheet, again, what forest existed in the region could have burned? George > > In sci.bio.paleontology George <geo...@yourservice.com> wrote: > [quoted text clipped - 25 lines] > > George If we think again the original meteorite theory mentined above, then we have following estimates from which we can possibly see that could this be possible at all in this case ? I found one program which calculates possible crater diameter, wood charred distance etc, if you give required parameters: http://www.bumply.com/astro.html#5 A. If you give parameters: object's diameter = 5000 m, icey, strike velocity = 20 km/s, target density = 1000 kg/m3, you get the following results from the calculator: crater diameter = 54579 m, 1 st degree burns = 23292.35 km, 3 rd degree burns = 13054.85 km, wood charred = 9643.95 km, white cotton ignites= 5208.3 km. B. If you give parameters: object's diameter = 5000 m, icey, strike velocity = 60 km/s, target density = 1000 kg/m3, you get the following results from the calculator: crater diameter = 104157 m, 1 st degree burns = 69877.1 km, 3 rd degree burns = 39164.6 km, wood charred = 28931.85 km, white cotton ignites= 15625 km. Huge numbers, many of these distances are greater than diameter of the Earth ? Please try the calculator program with your parameters. What you got ? Hannu >> > In sci.bio.paleontology George <geo...@yourservice.com> wrote: >> [quoted text clipped - 62 lines] > > Hannu I am very familiar with impact calculators. I use the one on the University of Arizona'a web site all the time. But you are missing the point here. If it strikes a 10,000 feet thick ice sheet in a remote area, there necessarily isn't going to be any forest that the resulting impact can burn because the entire landscape is covered by ***a 10,000 feet thick ice sheet***. George > I am very familiar with impact calculators. I use the one on the > University of Arizona'a web site all the time. But you are missing the > point here. If it strikes a 10,000 feet thick ice sheet in a remote area, > there necessarily isn't going to be any forest that the resulting impact > can burn because the entire landscape is covered by ***a 10,000 feet thick > ice sheet***. *Until* the object impacts. Do you think that ice would stop that size object from impacting whatever is beneath it with enough energy left to splash magma all over the damn planet and start fires on the other damn side of it? Maybe it would only result in steam, as you imply, but that's not what I saw on TV. :-) Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >> I am very familiar with impact calculators. I use the one on the >> University of Arizona'a web site all the time. But you are missing the [quoted text clipped - 12 lines] > > Bob Umm, Bob (I can call you bob, right?). You should take what you see on TV with a grain of salt. Using the University of Arizona's impact calculator and inputing data for a 5 km diameter bolide with a density of dense rock impacting (in this case, water, since ice isn't available as a target in the impact calculator) 10,000 meters of water, for an observer 1,000 km away, here's what we get: Your Inputs: Distance from Impact: 1000.00 km = 621.00 miles Projectile Diameter: 5000.00 m = 16400.00 ft = 3.10 miles Projectile Density: 3000 kg/m3 Impact Velocity: 11.00 km/s = 6.83 miles/s Impact Angle: 45 degrees Target Density: 1000 kg/m3 Target Type: Liquid Water of depth 3048.00 meters, over typical rock. Energy: Energy before atmospheric entry: 1.19 x 1022 Joules = 2.84 x 106 MegaTons TNT The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.0 x 107years Major Global Changes: The Earth is not strongly disturbed by the impact and loses negligible mass. The impact does not make a noticeable change in the Earth's rotation period or the tilt of its axis. The impact does not shift the Earth's orbit noticeably. Crater Dimensions: What does this mean? The crater opened in the water has a diameter of 48.9 km = 30.3 miles For the crater formed in the seafloor: Transient Crater Diameter: 25.3 km = 15.7 miles Transient Crater Depth: 8.94 km = 5.55 miles Final Crater Diameter: 38.7 km = 24 miles Final Crater Depth: 0.889 km = 0.552 miles The crater formed is a complex crater. At this impact velocity ( < 12 km/s), little shock melting of the target occurs. Thermal Radiation: What does this mean? At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage. Seismic Effects: What does this mean? The major seismic shaking will arrive at approximately 200 seconds. Richter Scale Magnitude: 8.7 Mercalli Scale Intensity at a distance of 1000 km: III. Felt quite noticeably by persons indoors, especially on upper floors of buildings. Many people do not recognize it as an earthquake. Standing motor cars may rock slightly. Vibrations similar to the passing of a truck. IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably. Ejecta: What does this mean? The ejecta will arrive approximately 494 seconds after the impact. At your position the ejecta arrives in scattered fragments Average Ejecta Thickness: 3.65 mm = 0.144 inches Mean Fragment Diameter: 570 micrometers = 22.4 1/1000 of an inch Air Blast: What does this mean? The air blast will arrive at approximately 3030 seconds. Peak Overpressure: 14900 Pa = 0.149 bars = 2.12 psi Max wind velocity: 33.2 m/s = 74.2 mph Sound Intensity: 83 dB (Loud as heavy traffic) Damage Description: Glass windows will shatter. So the impact doesn't spew hot lava all over the place since there is no fireball (thus, no thermal radiation damage), and certainly if it struck ice instead of water, the effects would likely be much less than this for this distance. >>> I am very familiar with impact calculators. I use the one on the >>> University of Arizona'a web site all the time. But you are missing the [quoted text clipped - 101 lines] > struck ice instead of water, the effects would likely be much less than > this for this distance. Here is the link, try it: http://www.lpl.arizona.edu/impacteffects/ George > >>> I am very familiar with impact calculators. I use the one on the > >>> University of Arizona'a web site all the time. But you are missing the [quoted text clipped - 107 lines] > > George Yes OK, I took a quick look to the reference text (link to this paper was found from your reference). I have also found one present possible dangerous asteroid. Here are references of it which I found: Present situation in the Risk Page (many of these will be removed when enough accurate measurements are available) NeoDys Risk Page http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?riskpage:0;main One present example (diameter=0.270 km, H=19.7, this is maybe dangerous) (99942) Apophis - impactor table Object: 99942 date MJD sigma sigimp dist +/- width stretch p_RE exp. en. PS YYYY/MM (RE) (RE) RE/ sig MT ------------------------------------------------------------------------------------------------ 2036/04/13.371 64796.371 -2.470 0.000 1.15 +/- 0.003 3.32E+03 2.07E-05 8.26E-03 -2.57 2042/04/13.720 66987.720 -2.494 0.000 1.41 +/- 0.000 1.12E+06 5.26E-08 2.10E-05 -5.24 2044/04/13.296 67718.296 -2.434 0.000 2.08 +/- 0.000 6.27E+05 3.57E-08 1.42E-05 -5.44 2069/04/13.078 76849.078 2.112 0.000 0.97 +/- 0.000 3.74E+05 4.41E-07 1.76E-04 -4.56 2069/10/15.971 77034.971 1.466 0.000 0.48 +/- 0.160 1.52E+06 3.81E-07 1.52E-04 -4.63 2072/10/15.333 78130.333 -3.870 0.000 0.48 +/- 0.089 6.09E+06 1.57E-10 6.26E-08 -8.03 2076/07/30.873 79514.873 2.720 1.214 34.89 +/- 26.902 1.49E+07 3.73E-11 1.44E-08 -8.69 Based on 1000 optical observations (of which 5 are rejected as outliers) from 2004/03/15.108 to 2006/08/16.627, and also on seven radar data points on 2005/01/27, 2005/01/29, 2005/01/31, 2005/08/07 and 2006/05/06. Coordinates are given on the Target Plane Unit is one Earth radius, but impact cross section has radius between 2.15 and 2.16 Earth radii http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:Apophis;main http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:Apophis;statpts;gif http://newton.dm.unipi.it/cgi-bin/neodys/neoibo?objects:Apophis;properel;gif http://earn.dlr.de/nea/099942.htm http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=99942;orb=1 (simulation of the orbit, possible impact velocity can be esitimated from this ?) Conversion of Absolute Magnitude (H) to Diameter http://cfa-www.harvard.edu/iau/lists/Sizes.html This is quite inaccurate method to estimate diameters, but it is only available method ? Hannu >> >>> I am very familiar with impact calculators. I use the one on the >> >>> University of Arizona'a web site all the time. But you are missing [quoted text clipped - 190 lines] > > Hannu As of August 5, 2006, the threat level for Apophis had been reduced to level 0. As for your question about estimating diameters, I don't have a good answer for you at this time. I'll check back with you if I figure one out. George > >> "George" <geo...@yourservice.com> wrote in message > [quoted text clipped - 201 lines] > > George I roughly estimated the velocity difference of Apophis and Earth (they are orbiting same direction quite close each others as we see in the simulation pictures referenced above) and I got that possible impact velosity would be about 1 km/s, if I calculated right ? The exact diamenter is little uncertain and there was an earlier estimation of H which was H=19.20, which gave range 430 m-970 m (http://earn.dlr.de/nea/99942.htm, printed 19.8.2005), but present estimation is 270 m ? How big tsunamis would this cause if it would hit in some ocean ? Hannu >> >> "George" <geo...@yourservice.com> wrote in message >> [quoted text clipped - 234 lines] > > Hannu According to the impact calculator, if the object is 270 meters in diameter, and consists of dense rock, and is traveling at 1 km/s at a 45 degree angle relative to the earth's surface, it will break up in the atmosphere at an altitude of 28,200 ft. If the object is 439 meters in diameter, then using the same parameters as before, the object will break up in the atmosphere at an altitude of 28,400 ft, which is an odd result. Using a diameter of 970 meters, the object would break up at 28,500 ft, again, an odd result. Obviously, either the program has some errors in the calculations, or else there is a minimum size and density required before an object will strike the earth, which I think is highly likely. That said, if such an object exploded over a densely populated area, it would be devastating, to say the least. George > >> "mathematician" <hapor...@luukku.com> wrote in message > [quoted text clipped - 250 lines] > > read more ? A. It would then be like "a shot with a shotgun" (v = about 1km/s, hit angle to the Earth's atmosphere = more close to 90 than 45 ?), many fragments of different sizes results ? How do we know that there is no big iron fragments included in the structure of Apophis ? If I remember right there was also some fragmented iron (?) meteorite which hit to Estonia about 2400 years ago (there was a TV-program some time ago about this in finnish TV) ? I just think that could these meteorites about 13000 years ago, about 2400 years ago and Apophis have anything properties in common ? B. I found an abstract from the net about determination of H (and also diameter) of Apophis: ( http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=998112 ) ---COPY BELOW----- Proceedings of the International Astronomical Union (2007), 2: 451-454 Cambridge University Press doi:10.1017/S1743921307003560 Published online by Cambridge University Press 03May2007 Contributed Papers Albedo and size of (99942) Apophis from polarimetric observations? Alberto Cellinoa1, Marco Delb?a1a2 and Edward F. Tedescoa3 a1 INAF-Osservatorio Astronomico di Torino, strada Osservatorio 20, 10025 Pino Torinese, Italy email: cellino@inaf.oato.it a2 Observatoire de la C?te d'Azur, BP 229, Nice, France email: delbo@obs-nice.fr a3 University of New Hampshire, USA email: Ed.Tedesco@unh.edu Abstract. We have obtained the first accurate determination of the albedo of (99942) Apophis, by means of polarimetric observations carried out at the VLT. The observations allowed us to obtain the slope of the polarization-phase curve of this object, from which an albedo estimate of 0.33 ? 0.04 could be obtained. From our observations we also obtained a new estimate of the absolute magnitude: H = 19.7 ? 0.2 (assuming G=0.25, which applies to S- and Q-type asteroids). Based on these results, we derive for the size of Apophis a value of 270 ? 30 meters. The accuracy of this size estimate is mostly related to uncertainties in H, whereas the obtained albedo value should be considered more robust. Our observations convincingly show that polarimetry is an effective and efficient tool to obtain accurate albedos and sizes for small and faint potentially hazardous asteroids. Key Words: Asteroids; polarization Footnotes ? Based on observations obtained at the European Southern Observatory (ESO), DDT request 276.C-5030 ---COPY ABOVE----- http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=998112 Hannu In sci.bio.paleontology mathematician <haporopu@luukku.com> wrote: Sheesh ... care to post edit next time? You don't have to post ALL the previous text with each post. SignatureThomas T. Veldhouse Software is like sex; it's better when it's free. -- Linus Torvalds To George: A. It would then be like "a shot with a shotgun" (v = about 1km/s, hit angle to the Earth's atmosphere = between 0 to 90 (45 is average estimate ?)), many fragments of different sizes results ? How do we know that there is no big iron fragments included in the structure of Apophis which could possible cause tsunamis if hit into ocean? If I remember right there was also some fragmented iron (?) meteorite which hit to Estonia about 2400 years ago (there was a TV-program some time ago about this in finnish TV) ? I just think that could these meteorites about 13000 years ago, about 2400 years ago and Apophis have anything properties in common (and maybe there exist also other possible years ) ??? I found one interesting reference (possible could be related to this phenomena if enough properties in common exists ???) but unfortunately I don't have that paper on my hands now: Kerr, R. A., 1992. Earth Gains a Retinue of Mini Asteroids. Science, vol. 258, no. 5081, Oct 16, p. 403. I must read this in the library. I comment it later if I find it. B. I found an abstract from the net about determination of H (and also diameter) of Apophis: http://journals.cambridge.org/action/displayAbstract?fromPage=online&... --COPY BELOW----- Proceedings of the International Astronomical Union (2007), 2: 451-454 Cambridge University Press doi:10.1017/S1743921307003560 Published online by Cambridge University Press 03May2007 Contributed Papers Albedo and size of (99942) Apophis from polarimetric observations† Alberto Cellinoa1, Marco Delbòa1a2 and Edward F. Tedescoa3 a1 INAF-Osservatorio Astronomico di Torino, strada Osservatorio 20, 10025 Pino Torinese, Italy email: cell...@inaf.oato.it a2 Observatoire de la Côte d'Azur, BP 229, Nice, France email: d...@obs-nice.fr a3 University of New Hampshire, USA email: Ed.Tede...@unh.edu Abstract. We have obtained the first accurate determination of the albedo of (99942) Apophis, by means of polarimetric observations carried out at the VLT. The observations allowed us to obtain the slope of the polarization-phase curve of this object, from which an albedo estimate of 0.33 ± 0.04 could be obtained. From our observations we also obtained a new estimate of the absolute magnitude: H = 19.7 ± 0.2 (assuming G=0.25, which applies to S- and Q-type asteroids). Based on these results, we derive for the size of Apophis a value of 270 ± 30 meters. The accuracy of this size estimate is mostly related to uncertainties in H, whereas the obtained albedo value should be considered more robust. Our observations convincingly show that polarimetry is an effective and efficient tool to obtain accurate albedos and sizes for small and faint potentially hazardous asteroids. Key Words: Asteroids; polarization Footnotes † Based on observations obtained at the European Southern Observatory (ESO), DDT request 276.C-5030 ---COPY ABOVE----- http://journals.cambridge.org/action/displayAbstract?fromPage=online&... Hannu (I'am sorry about I did not notice long reply texts which google generated automatically. They are quite annoying.) I found one discussion in the the of this article (Kerr, R. A., 1992. Earth Gains a Retinue of Mini Asteroids. Science, vol. 258, no. 5081, Oct 16, p. 403. ) ----Partly COPIED BELOW------ From: jsco...@lpl.arizona.edu (Jim Scotti x2717) Newsgroups: sci.astro,sci.space Subject: Re: "Earth Gains a Retinue of Mini-Asteroids" Message-ID: <1992Oct31.075547.28204@organpipe.uug.arizona.edu> Date: 31 Oct 92 07:55:47 GMT References: <1992Oct29.170729.20363@cs.rochester.edu> Sender: n...@organpipe.uug.arizona.edu Distribution: na Organization: Lunar & Planetary Laboratory, Tucson AZ. Lines: 66 In article <1992Oct29.170729.20...@cs.rochester.edu> d...@cs.rochester.edu (Paul Dietz) writes: >Science (10/16/92, page 403), reports that Gehrels and colleagues in >the Spacewatch program have detected 8 very near earth asteroids over [quoted text clipped - 7 lines] >body, and such events were calculated to occur once every 2 to 3 >centuries, something is screwy here. Not really screwy. The number of 50 meter objects is enhanced by about 10 times and the Tunguska type events probably happen once or a few times per century. Remember, 3 out of 4 enter over water and may be less likely to be detected. Also, perhaps a large fraction of them disintegrate higher in the atmoshpere, causing a much smaller disturbance in the lower atmosphere than that of the Tunguska event. Also, the best guess I've heard for the size of the Tunguska progenitor is between 50 and 100 meters. The 10 meter sized objects are enhanced by a factor of 100 and the trend from the larger objects to the smallest is a gradual transition that starts at around 100 meters size. >The orbits of the bodies are unexpectedly similar to Earth's. >Two have orbits more like earth's than any known body; one was that >asteroid that was mistaken for a spent rocket body. Also known as 1991 VG. >These couldn't be Frank's minicomets, could they? His putative >objects are supposedly in prograde, earth-like orbits, to reduce the >impact velocity enough to avoid observational constraints. Frank's minicomets were estimated to be 10-30 meters in size. The number of objects in this size that he estimated to account for what was probably detector noise was at least a million times the the number extrapolated from the larger Near Earth asteroid population and therefore is a population at least 10,000 times more numerous than what has now been found by Spacewatch. In short, with our sensitivity, we should see at least 1000 of Frank's minicomets each NIGHT!!!!!! I think the Spacewatch survey has now effectively disproven Frank's hypothesis used to explain his so called "atmospheric holes". Incidentally, an earlier CCD developed by Spacewatch in the early 1980's (an old RCA 320x512 chip) was used by a colleague of Frank's from JPL to survey for the minicomets directly. This investigator claimed to have detected at least one such object on two consecutive images. Without consulting the Spacewtach crew, he announced his "discovery". When we were finally able to look at his images, we concluded that what he was looking at was detector noise! > Paul F. Dietz > d...@cs.rochester.edu Jim. --------------------------------------------- Jim Scotti {jsco...@lpl.arizona.edu} Lunar & Planetary Laboratory University of Arizona Tucson, AZ 85721 USA From: jsco...@lpl.arizona.edu (Jim Scotti x2717) Newsgroups: sci.space Subject: Re: "Earth Gains a Retinue of Mini-Asteroids" Message-ID: <1992Nov4.204744.15077@organpipe.uug.arizona.edu> Date: 4 Nov 92 20:47:44 GMT References: <Bx3CM5.7Gx.1@cs.cmu.edu> Sender: n...@organpipe.uug.arizona.edu Distribution: sci Organization: Lunar & Planetary Laboratory, Tucson AZ. Lines: 62 In article <Bx3CM5.7G...@cs.cmu.edu> a...@elegabalus.cs.qub.ac.uk writes: {Actually, I (jsco...@lpl.arizona.edu) wrote this:} >> Not really screwy. The number of 50 meter objects is enhanced by >> about 10 times and the Tunguska type events probably happen once [quoted text clipped - 5 lines] >late 70's - early 80's? It was never connected to any source that I >am aware of. I vaguely remember hearing something about this. The rate of small asteroid impact could very well account for such an event. I doubt we can conclusively identify it as an asteroid impact, but the probability of such an event happening is quite high. >Some theorized it was caused by an undersea volcanic explosion, but >no one succeeded in associating it with one. It was not a nuclear >explosion, although some at first suggested that. It is unlikely to >have been a non-nuclear explosion, ie no ships disappeared and I'm >not sure I see a motive for an experimental blast in that part of the >world. In the absence of further evidence, we'll just have to add small asteroid impacts as a possibility. >Just a thought, although I would not expect a mushroom cloud from >such a comet strike. I'm not sure I can even see a mechanism for >creating one from a Tunguska class strike. The mechanism is quite understandable. You have an object moving at hypersonic velocity as it enters the atmosphere. A stony or stony iron object could easily survive into the low atmosphere where the aerodynamical stress catastrophically ruptures it and it explodes just like a bomb. The estimated impact energies of 10-100 meter objects traveling at typical velocities is measured in the kilotons on the small end to 10s of megatons on the large end and that kinetic energy has to go somewhere! Smaller objects fracture high in the atmosphere and appear as bright bolides which leave trails and fragments along the way. If the object is strong enough, it might survive largely intact with most of its kinetic energy and might create an impact crater such as was made about 50,000 years ago when the Diablo Canyon Meteor crater was formed in Arizona. That crater is thought to have been formed by the impact of a stony iron object only about 30 meters in diameter. Objects strong enough to survive atmospheric entry are fortunately rare. By the way, the Tuguska event was observed by residents of the region and their description of the explosion matchs that of a nuclear bomb blast quite closely. Jim. --------------------------------------------- Jim Scotti {jsco...@lpl.arizona.edu} Lunar & Planetary Laboratory University of Arizona Tucson, AZ 85721 USA --------------------------------------------- From: jsco...@lpl.arizona.edu (Jim Scotti x2717) Newsgroups: sci.astro,sci.space Subject: Re: "Earth Gains a Retinue of Mini-Asteroids" Message-ID: <1992Nov7.011656.14470@organpipe.uug.arizona.edu> Date: 7 Nov 92 01:16:56 GMT References: <1992Oct29.170729.20363@cs.rochester.edu> <1992Oct31.075547.28204@organpipe.uug.arizona.edu> <BxACCF.D3A@techbook.com> Sender: n...@organpipe.uug.arizona.edu Distribution: na Organization: Lunar & Planetary Laboratory, Tucson AZ. Lines: 44 In article <BxACCF....@techbook.com> d...@techbook.com (Dan Tilque) writes: >jsco...@lpl.arizona.edu (Jim Scotti x2717) writes: >>d...@cs.rochester.edu (Paul Dietz) writes: [quoted text clipped - 14 lines] > >Anyone know about this? Yup, I do. You are remembering the meteorite fall called "Sikhote- Alin" which happened in 1947 in Siberia. The fall created about 200 small craters of the non-explosive type created by the fall of large objects traveling relatively slowly, perhaps at terminal velocity. The largest crater was about 26.5 meters in diameter. I think that about 50 tons of material was recovered and the progenitor was estimated as being about 200 tons before atmospheric entry. I suppose the object would have been around 5 meters diameter before entry and was probably a stoney iron. This size object probably hits the Earth around 10 times per year and I suppose about 1% of them are stoney iron, so a fall of this type probably happens on the order of once a decade. >--- >Dan Tilque -- d...@techbook.com Jim. --------------------------------------------- Jim Scotti {jsco...@lpl.arizona.edu} Lunar & Planetary Laboratory University of Arizona Tucson, AZ 85721 USA --------------------------------------------- ----COPY ABOVE-------------------- Hannu >> *Until* the object impacts. Do you think that ice would stop that >> size object from impacting whatever is beneath it with enough energy [quoted text clipped - 5 lines] > > Umm, Bob (I can call you bob, right?). Sure. > You should take what you see on TV > with a grain of salt. :-) Just didn't want you to think I thought I knew what I was talking about. > So the impact doesn't spew hot lava all over the place since there is > no fireball (thus, no thermal radiation damage), and certainly if it struck > ice instead of water, the effects would likely be much less than this for > this distance. Thanks. The one that wiped out the dinosaurs was the one I saw reported on a TV show and the simulation showed molten stuff splashing thousands of miles up into North America lighting fires all over hell and back. Bad science reporting or a much bigger event? Bob Signature"Things should be described as simply as possible, but no simpler." A. Einstein >>> *Until* the object impacts. Do you think that ice would stop that >>> size object from impacting whatever is beneath it with enough energy [quoted text clipped - 28 lines] > > Bob Probably both. George |
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