INCOMING!: метеорита в Челябинске, Russian Meteor - February 2013 |
INCOMING!: метеорита в Челябинске, Russian Meteor - February 2013 |
Feb 15 2013, 07:01 AM
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Senior Member Group: Moderator Posts: 3241 Joined: 11-February 04 From: Tucson, AZ Member No.: 23 |
Looks like a small meteoroid decided to spoil 2012 DA14's big day by exploding over Russia...
http://zyalt.livejournal.com/722930.html?nojs=1 -------------------- &@^^!% Jim! I'm a geologist, not a physicist!
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Feb 15 2013, 04:08 PM
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Member Group: Members Posts: 723 Joined: 13-June 04 Member No.: 82 |
I am trying to get an estimate of the size of the meteoroid and explosion. Assuming a dense rocky composition with a density around 3 tonnes per cubic metre, I keep getting sizes much larger than the estimate of around 10 tonnes that I have heard. The calculation below results in a mass of around 73,000 tonnes.
The overpressure from the blast wave was sufficient to shatter thousands of windows (and in fact some videos I have watched appear to show that every window in view was smashed) and caused the partial collapse of a zinc factory. This implies that the overpressure was between 1 kPA (shatters many windows) and 5 kPa (partial collapse of some buildings), let's assume that the zinc factory was poorly maintained and the overpressure was 3 kPa. Early reports give an entry velocity of around 30 km/s. According to this site, the diameter of a rocky object that produces a 3.1 kPa overpressure at a distance of 30 km from directly under the main explosion (as appears to be roughly the distance from the videos) would be about 36m, producing a 5.26 MT airburst at an altitude of 18.2 km. Earth Impact Effects Program Robert Marcus, H. Jay Melosh, and Gareth Collins Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article Your Inputs: Distance from Impact: 30.00 km ( = 18.60 miles ) Projectile diameter: 36.00 meters ( = 118.00 feet ) Projectile Density: 3000 kg/m3 Impact Velocity: 30.00 km per second ( = 18.60 miles per second ) Energy: Energy before atmospheric entry: 3.30 x 10^16 Joules = 7.88 MegaTons TNT The average interval between impacts of this size somewhere on Earth is 539.1 years 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 tilt of Earth's axis (< 5 hundreths of a degree). The impact does not shift the Earth's orbit noticeably. Atmospheric Entry: The projectile begins to breakup at an altitude of 63100 meters = 207000 ft The projectile bursts into a cloud of fragments at an altitude of 18200 meters = 59600 ft The residual velocity of the projectile fragments after the burst is 17.3 km/s = 10.7 miles/s The energy of the airburst is 2.20 x 10^16 Joules = 5.26 MegaTons. No crater is formed, although large fragments may strike the surface. Air Blast: The air blast will arrive approximately 1.77 minutes after impact. Peak Overpressure: 3100 Pa = 0.031 bars = 0.44 psi Max wind velocity: 7.21 m/s = 16.1 mph Sound Intensity: 70 dB (Loud as heavy traffic) edit -- Assuming that the distance from ground zero was 15km instead of 30km, and with an overpressure of 2 kPa, the website gives the following (calculated initial mass 51,000 tonnes): Your Inputs: Distance from Impact: 15.00 km ( = 9.32 miles ) Projectile diameter: 32.00 meters ( = 105.00 feet ) Projectile Density: 3000 kg/m3 Impact Velocity: 30.00 km per second ( = 18.60 miles per second ) Energy: Energy before atmospheric entry: 2.32 x 10^16 Joules = 5.53 MegaTons TNT The average interval between impacts of this size somewhere on Earth is 410.7 years 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 tilt of Earth's axis (< 5 hundreths of a degree). The impact does not shift the Earth's orbit noticeably. Atmospheric Entry: The projectile begins to breakup at an altitude of 63100 meters = 207000 ft The projectile bursts into a cloud of fragments at an altitude of 19900 meters = 65400 ft The residual velocity of the projectile fragments after the burst is 18.3 km/s = 11.4 miles/s The energy of the airburst is 1.45 x 10^16 Joules = 3.47 MegaTons. No crater is formed, although large fragments may strike the surface. Air Blast: The air blast will arrive approximately 1.26 minutes after impact. Peak Overpressure: 2120 Pa = 0.0212 bars = 0.301 psi Max wind velocity: 4.96 m/s = 11.1 mph Sound Intensity: 67 dB (Loud as heavy traffic) another edit -- this is the minimum value that reliably breaks windows, it still results in a calculated airburst energy of 1.9 MT with an initial mass of 31,000 tonnes. I doubt that the airburst was this close to overhead, it appeared closer to the horizon in the videos. Your Inputs: Distance from Impact: 10.00 km ( = 6.21 miles ) Projectile diameter: 27.00 meters ( = 88.60 feet ) Projectile Density: 3000 kg/m3 Impact Velocity: 30.00 km per second ( = 18.60 miles per second ) Energy: Energy before atmospheric entry: 1.39 x 10^16 Joules = 3.32 MegaTons TNT The average interval between impacts of this size somewhere on Earth is 277.4 years 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 tilt of Earth's axis (< 5 hundreths of a degree). The impact does not shift the Earth's orbit noticeably. Atmospheric Entry: The projectile begins to breakup at an altitude of 63100 meters = 207000 ft The projectile bursts into a cloud of fragments at an altitude of 22500 meters = 73700 ft The residual velocity of the projectile fragments after the burst is 19.6 km/s = 12.2 miles/s The energy of the airburst is 7.95 x 10^15 Joules = 1.90 MegaTons. No crater is formed, although large fragments may strike the surface. Air Blast: The air blast will arrive approximately 1.24 minutes after impact. Peak Overpressure: 994 Pa = 0.00994 bars = 0.141 psi Max wind velocity: 2.33 m/s = 5.22 mph Sound Intensity: 60 dB (Loud as heavy traffic) |
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