[math-fun] Size of the Cherbakul Lake Meteorite Fragment
From a National Post (newspaper) article today: "Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake." When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
* Hans Havermann <gladhobo@teksavvy.com> [Feb 18. 2013 19:38]:
From a National Post (newspaper) article today:
"Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake."
When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
In short: impact above a certain speed is an explosive event. Half a ton of material at the speed (exceeding that) of a bullet will at the very least create a neat shock wave inside the water, certainly leaving a much greater hole than its diameter. I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out. The latter seems more plausible to me.
Couldn't the meteorite have been hot enough so that the smaller ice fragments were melted by the warmer water? Or was the photo taken almost immediately upon impact? --Dan On 2013-02-18, at 11:01 AM, Joerg Arndt wrote:
* Hans Havermann <gladhobo@teksavvy.com> [Feb 18. 2013 19:38]:
From a National Post (newspaper) article today:
"Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake."
When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
In short: impact above a certain speed is an explosive event.
Half a ton of material at the speed (exceeding that) of a bullet will at the very least create a neat shock wave inside the water, certainly leaving a much greater hole than its diameter.
I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out. The latter seems more plausible to me.
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Supposedly (I have no personal experience), meteors are very cold inside (3K?) and the heat of reentry doesn't penetrate deeply. And a newly fallen meteor often has a layer of frost (when found), drawn from the air. Even in a more moderate climate than the Urals. If this is true, a fragment moving at only terminal velocity (a few hundred MPH) would not deliver much heat energy when it hit a frozen over lake. The impact would make a hole from mechanical forces. Maybe someone here can explain why the hole is a circle, instead of an irregular shape. Rich ------ Quoting Dan Asimov <dasimov@earthlink.net>:
Couldn't the meteorite have been hot enough so that the smaller ice fragments were melted by the warmer water? Or was the photo taken almost immediately upon impact?
--Dan
On 2013-02-18, at 11:01 AM, Joerg Arndt wrote:
* Hans Havermann <gladhobo@teksavvy.com> [Feb 18. 2013 19:38]:
From a National Post (newspaper) article today:
"Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake."
When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
In short: impact above a certain speed is an explosive event.
Half a ton of material at the speed (exceeding that) of a bullet will at the very least create a neat shock wave inside the water, certainly leaving a much greater hole than its diameter.
I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out. The latter seems more plausible to me.
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On 2/18/2013 2:42 PM, rcs@xmission.com wrote:
Supposedly (I have no personal experience), meteors are very cold inside (3K?) and the heat of reentry doesn't penetrate deeply. And a newly fallen meteor often has a layer of frost (when found), drawn from the air. Even in a more moderate climate than the Urals. If this is true, a fragment moving at only terminal velocity (a few hundred MPH) would not deliver much heat energy when it hit a frozen over lake. The impact would make a hole from mechanical forces. Maybe someone here can explain why the hole is a circle, instead of an irregular shape.
I can't say I've studied it enough to explain it, but I've observed that even projectiles that hit the earth obliquely tend to make circular craters. For example, the meteorite that made the Great Meteor Crater in Arizona, which is quite circular, was found under one wall of the crater, not in the center. And I have some video of 20mm canon fire hitting the ocean surface at a very low angle of elevation. The splashes are almost circular. Brent
Rich
------ Quoting Dan Asimov <dasimov@earthlink.net>:
Couldn't the meteorite have been hot enough so that the smaller ice fragments were melted by the warmer water? Or was the photo taken almost immediately upon impact?
--Dan
On 2013-02-18, at 11:01 AM, Joerg Arndt wrote:
* Hans Havermann <gladhobo@teksavvy.com> [Feb 18. 2013 19:38]:
From a National Post (newspaper) article today:
"Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake."
When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
In short: impact above a certain speed is an explosive event.
Half a ton of material at the speed (exceeding that) of a bullet will at the very least create a neat shock wave inside the water, certainly leaving a much greater hole than its diameter.
I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out. The latter seems more plausible to me.
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meekerdb:
I've observed that even projectiles that hit the earth obliquely tend to make circular craters.
To whet our mathematical appetites, Stefan Geens has done an admirable job of estimating a final approach trajectory: http://ogleearth.com/2013/02/reconstructing-the-chelyabinsk-meteors-path-wit...
Joerg Arndt:
I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out.
In the last hour I heard meteorologist Chad Myers of/on CNN pass on (as though he believed it was true) the initially/occasionally expressed notion that this was an ice-fishing hole. I had to smile.
I heard one report that scuba divers had already tried to find fragments in the lake. Perhaps the (round) hole was dug for the divers? At 11:15 AM 2/19/2013, Hans Havermann wrote:
Joerg Arndt:
I note the (apparent) lack of ice fragments swimming inside the hole and speculate that either the ice in question was immediately rendered into less than even small fragments, or fragments (where not "atomized" and) got thrown out.
In the last hour I heard meteorologist Chad Myers of/on CNN pass on (as though he believed it was true) the initially/occasionally expressed notion that this was an ice-fishing hole. I had to smile.
Henry Baker:
I heard one report that scuba divers had already tried to find fragments in the lake. Perhaps the (round) hole was dug for the divers?
I've watched more recent news video footage showing the hole already mostly frozen over. It will be spring before they do more diving.
Russia pulls huge 'Chelyabinsk meteor chunk' from lake (AFP): "Much of the meteor landed in a local lake called Chebarkul that the divers entered on Wednesday in an operation covered live on Russian television. Live footage showed a team pull out a 1.5-metre-long (five-foot-long) rock from the lake after first wrapping it in a special casing while it was still underwater." On Feb 18, 2013, at 12:38 PM, Hans Havermann <gladhobo@teksavvy.com> wrote:
From a National Post (newspaper) article today:
"Viktor Grokhovsky, who led the expedition from Urals Federal University, said Monday the meteorites plucked from the ice-covered Chebarkul Lake so far are less than a centimeter and had an iron content of about 10 percent. Locals saw a big meteorite fall into the lake on Friday, leaving a six-meter-wide hole in the ice. Grokhovsky said a meteorite up to 50-60 centimeters could eventually be found in the lake."
When the initial reports of the 6 m hole surfaced, I thought (looking at a picture of the hole in the ice): That must be a 4 m (or more) chunk of rock. But .5 m? An impact in a surface ice layer surely is not like an impact on ground where a wider hole might be expected.
participants (6)
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Dan Asimov -
Hans Havermann -
Henry Baker -
Joerg Arndt -
meekerdb -
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