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10ft asteroid just missed us Fri., Oct 19th


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A ten foot diameter asteroid, called 2018UA, just missed hitting the Earth by just a few hundred miles on Friday, Oct 19, 2018. It was not discovered until it had already passed us. Over Mesa, Arizona it would have been visible in a moderate telescope at +11 magnitude Friday night. It's elliptical orbit goes from Venus's orbit to beyond Mars. You can find the orbital elements for this one and many other visible near Earth objects at http://spaceweather.com/ by clicking on the asteroid and putting in your coordinates.

It would have been more exciting if it had landed on land nearby as there would be hundreds to thousands of fragments in a strewnfield below. 

Sorry fellas. We'll have to wait for the next one.

billpeters

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On 10/24/2018 at 5:55 PM, billpeters said:

A ten foot diameter asteroid, called 2018UA, just missed hitting the Earth by just a few hundred miles on Friday, Oct 19, 2018. It was not discovered until it had already passed us. Over Mesa, Arizona it would have been visible in a moderate telescope at +11 magnitude Friday night. It's elliptical orbit goes from Venus's orbit to beyond Mars. You can find the orbital elements for this one and many other visible near Earth objects at http://spaceweather.com/ by clicking on the asteroid and putting in your coordinates.

It would have been more exciting if it had landed on land nearby as there would be hundreds to thousands of fragments in a strewnfield below. 

Sorry fellas. We'll have to wait for the next one.

billpeters

Be careful what you wish for :)  One of about that size (a bit larger) exploded over Russia in 2013, with the force of 500 KT of TNT--more powerful than the atomic bomb dropped on Hiroshima. Fortunately, it exploded 20 miles up and most of the blast was absorbed by the atmosphere.  Still, it caused damage and thousands of injuries in the nearby town of Chelyabinsk (most from broken glass).  There were surviving pieces to be collected, including a fairly good-sized chunk that fell into a frozen lake.

https://en.wikipedia.org/wiki/Chelyabinsk_meteor

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Actually the asteroid 2018UA, approximately 3 meters in diameter, has 1242 times less volume than the 20 meter wide Chelyabinsk Meteorite event of 2013, which injured 1700 people. Contrary to popular belief, meteorites have actually killed people, including the June 30, 1908 Tunguska event, which killed one person blown against a tree and a second elderly man who succumbed to his injuries shortly thereafter (poorly documented in English in the West). An 18th century French aspiring priest was struck and killed with a clear description of the event and meteorite with drawings of the stone. In the late 19th century the actual meteorite was lost from the nearby monastery, but the documentation is solid. Sky and Telescope did an article on reasonable historical accounts of people killed by meteorites about ten years ago.

I want them big enough to find, but not so big that they hurt someone.

billpeters

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Same order of magnitude for diameters, anyway. A few higher, and you are talking extinction-level events.  The one that killed the dinosaurs (including 75% of all species of life on earth) was only 10km or so.

Fascinating stuff about the fatalities--did not realize there were actual documented deaths.  But easy to see the potential, even with small bolides.  The Chelyabinsk Meteorite, if it had held together a few seconds longer, could have taken out a city.

Note that astronomers did not see the Chelyabinsk Meteorite coming until it hit (i.e., not at all). Of course, it's easier to spot the larger ones.  But, I am pessimistic about the chances of us spotting even a 5-mile rock coming in time to do anything about it. 

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EDIT #1: I knew I should have posted this when I typed it up Wed AM..

Bill / anyone,

I have a couple questions. If someone would point me to a website containing the formulas I need that would be fine, but if anyone feels like laying out the answers...

The Qs are in comparison to Chelyabinsk fall (making the assumption of similar composition for weight and volume/area) and what I'm after is this:

Given Chelyabinsk was 60 feet (is that cubed feet or spherical volume or something else, btw?) and exploded 12 mi 'up' @ equivalent of 500 megatons, how does one figure the size ratio potential of strike damage difference (assuming unbroken landfall) and explosive force difference (assuming explosion) of the 10 foot 2018UA in comparison?
Is it a straight 1-to-6 ratio or does the force increase / decrease exponentially based on size/volume for either or both possibilities? As in: if 2018UA followed the same trajectory and also exploded 12 miles up, would it have only done 1/6th the damage or is there a  + - factor of some sort at play also.

Thanks,

Swamp

EDIT #2: When I cubed their sizes I ended up with 1,000 cu ft vs 216,000 cu ft, which still leaves me well short of 1242 X less volume.. And when I took volume size difference times itself (1x2x3etc=720) I only came out to 720 X, still well short.. I couldn't remember the formula for spherical volume ( is that x = 2(pi)r )? Regardless, that would have been well short of 1242 as well.. So basically, I'm lost in re the formulas I'm seeking..

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8 hours ago, Swampstomper Al said:

EDIT #1: I knew I should have posted this when I typed it up Wed AM..

Bill / anyone,

I have a couple questions. If someone would point me to a website containing the formulas I need that would be fine, but if anyone feels like laying out the answers...

The Qs are in comparison to Chelyabinsk fall (making the assumption of similar composition for weight and volume/area) and what I'm after is this: 

Given Chelyabinsk was 60 feet (is that cubed feet or spherical volume or something else, btw?) and exploded 12 mi 'up' @ equivalent of 500 megatons, how does one figure the size ratio potential of strike damage difference (assuming unbroken landfall) and explosive force difference (assuming explosion) of the 10 foot 2018UA in comparison?
Is it a straight 1-to-6 ratio or does the force increase / decrease exponentially based on size/volume for either or both possibilities? As in: if 2018UA followed the same trajectory and also exploded 12 miles up, would it have only done 1/6th the damage or is there a  + - factor of some sort at play also. 

Thanks,

Swamp

EDIT #2: When I cubed their sizes I ended up with 1,000 cu ft vs 216,000 cu ft, which still leaves me well short of 1242 X less volume.. And when I took volume size difference times itself (1x2x3etc=720) I only came out to 720 X, still well short.. I couldn't remember the formula for spherical volume ( is that x = 2(pi)r )? Regardless, that would have been well short of 1242 as well.. So basically, I'm lost in re the formulas I'm seeking.. 

Google does all the work for me with its calculator:

https://www.google.com/search?ei=6AHbW9DiFLXK0PEPiPC2OA&q=volume+of+a+sphere+calculator&oq=volume+of+a+sphere&gs_l=psy-ab.3.0.0i71l8.0.0..5659...0.0..0.0.0.......0......gws-wiz.YvfpIdj5acg

10' diameter 523 ft squared

20' diameter 4188 ft squared

40' diemeter 33510

Just remember the meteors widths are given and the formula uses the radius, or half the width.

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2 hours ago, chrisski said:

Google does all the work for me with its calculator:..

Thanks for this Chris..

But the question remains if/is this the formula used to approximate / estimate a meteor's mass / volume when only one dimension is given (which I always take to be its length?)

I did say sphere above, but maybe cylinder would provide a more accurate inaccuracy?? I dunno.. I'm just going for an approximation.. Which makes me wonder if the sky guys have some type of tweaked formula they use  based on the one dimension ultimately being the total extent of information known about the object?

Swamp

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15 hours ago, Dubious said:

Same order of magnitude for diameters, anyway. A few higher, and you are talking extinction-level events.  The one that killed the dinosaurs (including 75% of all species of life on earth) was only 10km or so.

Fascinating stuff about the fatalities--did not realize there were actual documented deaths.  But easy to see the potential, even with small bolides.  The Chelyabinsk Meteorite, if it had held together a few seconds longer, could have taken out a city.

Note that astronomers did not see the Chelyabinsk Meteorite coming until it hit (i.e., not at all). Of course, it's easier to spot the larger ones.  But, I am pessimistic about the chances of us spotting even a 5-mile rock coming in time to do anything about it. 

Hey Dubie,

I did make an error on the volume ratio with the correct ratio for the Chelyabinsk event as 296 times more energetic/massive. The volume formula is :  V=4/3π r . Everything in the formula cancels out when comparing two spheres except the radius, which is cubed giving the ratio.  Since the radius of Chelyabinsk is 6.666 times larger than the 2018 UA asteroid simply cube the radius, which is correctly 296 times larger -equal to the energy/volume equivalent.

Asteroids are measured by their estimated spherical volume. Most potato shaped asteroids are still relatively spherical. Of the 1.6 million asteroids observed so far the most elongated in OUR Solar System has a ratio of 3.5 to 1.  It is difficult for an asteroid to form elongated. And it is logically more difficult to maintain that shape without breaking or collapsing down to a potato rubble. Binaries commonly form and are stable, but their ratio rarely exceeds 1.8 to 1. You cannot get three binaries stably in a row.  The 10:1 ratio of the first discovered interstellar asteroid Oumuama is unique and difficult to explain.

The following is a crater impact calculator to run you own scenarios:  http://down2earth.eu/impact_calculator/input.html?lang=en&planet=Earth

billpeters

P.S. We have statistically discovered about 95% of all PHAs 1 km in diameter. Nothing is headed our way. Oort Cloud comets, first time visitors, are the only reasonable large threat.

 

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I'm afraid of that 5%--the devil is usually in the details :)  Also, there are a lot of objects in the Oort Cloud (to put it mildly), and I believe some theories have it disturbed periodically, sending many winging through the inner solar system.  In the fullness of time, it is absolutely certain that a bolide as larger or larger than the one that hit 65 million years ago will again strike the earth (if not stopped).

On the explosive force/impact question, you want to consider not only mass, but also velocity and composition (some types would hold together better).

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Dubie,

The impact calculator website I sited accounts for velocity and composition.  Please note that nearly all large meteorites found are irons which compose only 3.5% of all meteorites with pallasites next. H-stoneys (5-25~% higher iron content) are next in large size discoveries with the L-stoneys (below 5~% iron content) and carbons usually only smaller pieces.  The composition versus surviving size is obvious.

The 5% undiscovered PHAs are actually less of a threat since they are mostly in syncopated orbits that come close to Earth's orbit whenever we are not there and, thus, are never close enough to be easily found.

No dwarf or other star system have passed within a light year or two in a very long time. Nothing else is expected for about 1,450,000 years. 

Relax.

billpeters

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9 hours ago, Swampstomper Al said:

Thanks for this Chris..

But the question remains if/is this the formula used to approximate / estimate a meteor's mass / volume when only one dimension is given (which I always take to be its length?)

I did say sphere above, but maybe cylinder would provide a more accurate inaccuracy?? I dunno.. I'm just going for an approximation.. Which makes me wonder if the sky guys have some type of tweaked formula they use  based on the one dimension ultimately being the total extent of information known about the object?

Swamp

I'd be very skeptical of any cosmic estimate.  I really think a lot of these are "Best Guesses" based of very incomplete data.  The Russian event was recorded on video, and getting a size would be extremely difficult.  I've had to pull a precise number out of a very wide ranging estimate when my bosses needed some a very precise number to help them plan.  I really think that type of stuff is the same and in order to get a headline, or a bullet point, a number is given that is very wide ranging.

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9 hours ago, billpeters said:

...I did make an error on the volume ratio with the correct ratio for the Chelyabinsk event as 296 times more energetic/massive. The volume formula is :  V=4/3π r . Everything in the formula cancels out when comparing two spheres except the radius, which is cubed giving the ratio.  Since the radius of Chelyabinsk is 6.666 times larger than the 2018 UA asteroid simply cube the radius, which is correctly 296 times larger -equal to the energy/volume equivalent...

Ok, this (296x) makes a whole lot more sense than that 1242x energy/mass difference solution..
And thanks Chris & Bill for refreshing the sphere volume formula for me..

Swamp

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20 hours ago, Swampstomper Al said:

Thanks for this Chris..

But the question remains if/is this the formula used to approximate / estimate a meteor's mass / volume when only one dimension is given (which I always take to be its length?)

I did say sphere above, but maybe cylinder would provide a more accurate inaccuracy?? I dunno.. I'm just going for an approximation.. Which makes me wonder if the sky guys have some type of tweaked formula they use  based on the one dimension ultimately being the total extent of information known about the object? 

Swamp

We had formulas for this stuff when I used to do demo, but they were never spot on accurate.  There were minimum safe distances based off the force of the explosive, but frequently debris would fly further.  The formula we solved for had the letter P as the solution, which either stood for Pounds or Plenty.  Just doing demo a few times a couple of decades ago, I can't see how they can realistically calculate the blast of a meteor to any accuracy based on unknown or very roughly known or guessed height, Mass, and speed.

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daytime, three witnesses to old woman fall 1975. one glamis reported it barely cleared the chocolate mountains, size of a semi truck with flame streaking north. two witness in smoke tree saw it just clearing the palo verde mountains. line on a map from glamis to palo verde mountains puts it in the old woman mountain.

one of the old woman witnesses witnessed the smoke tree fall in 2005. while south bound on hwy 78 south of palo verde ca., at night. a fireball size of a volkswagon streaking in an southwesterly direction at a steep angle, 50-60 degrees disappeared over a rise. when he got to the rise, a fire was burning out in smoke tree.

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10 hours ago, chrisski said:

We had formulas for this stuff when I used to do demo, but they were never spot on accurate.  There were minimum safe distances based off the force of the explosive, but frequently debris would fly further.  The formula we solved for had the letter P as the solution, which either stood for Pounds or Plenty.  Just doing demo a few times a couple of decades ago, I can't see how they can realistically calculate the blast of a meteor to any accuracy based on unknown or very roughly known or guessed height, Mass, and speed.

You just made me go n dig out my copy of "Blasters' Handbook.."
Where's nugget108 when ya need him..? :miner:

Swamp

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