NEO Impact risks

[Leo S]

Sorry to steal some of your doom and gloom John, but I think the more immediate and pressing threat to us (besides ourselves) is the threat from NEOs, especially asteroids.

They keep underestimating the frequency at which larger scale impacts occur. When I first became interested in the subject in 1998/99 they estimated Tunguska/Chelyabinsk class impactors (large enough to devastate a city) occurred at a frequency of perhaps once every 100-150 years on average, but I think 50-100 years is what most have thought in recent times, however I would say 25-50 is closer to the reality (or perhaps even less), especially given the recent revaluations (see link above).

This map of larger impacts in the last 35 years from the US DOD puts Chelyabinsk into context quite well.

We are less likely to get hit by something that would destroy the planet or large region thankfully, but still very vulnerable to Tunguska/Chelyabinsk class objects, and it's basically luck if we see none in the next decade, but 1, 2 or perhaps 3 might be possible if we are unlucky.

Personally I say get a camera up to catch them if you can - even the smaller asteroids, like this one my camera caught last year, are impressive to behold, and the more footage we have the more we learn how to defeat the potential threat.

I think we already know that there are no near neighboring stars that pose a serious threat if they blow, and even if one did there would be nothing much we could do about it.

Edited June 23, 2023 by Leo S

[iantaylor2uk]

I think it's very unlikely a near earth object would destroy our planet, but it could potentially lead to extinction of some lifeforms on the planet.

[Leo S]

9 hours ago, iantaylor2uk said:

I think it's very unlikely a near earth object would destroy our planet, but it could potentially lead to extinction of some lifeforms on the planet.

Yes of course, a planet destroying impact is very unlikely - after all our planet is still here after billions of years (and some enormous hits), and I don't think an impact large enough to cause a global catastrophe is likely either. Most of the larger potential impactors (eg Apophis) have already been found, and we are also fast developing ways of deflecting larger asteroids (NASA's recent DART mission was a great success), so that is much less of a worry.

But there is another class of impactors which IS worrying. They are smaller, making them harder to spot, and there are also many more of them wizzing around us - as a rough rule, there is an order of magnitude less objects for every size class UP, so for every asteroid impact capable of destroying a region, there are perhaps 10 impacts capable of killing a city. These are in the 50-100m size range, like the Tunguska and Chelyabinsk impacts, and although they may not be global killers, they have the potential to cause a great deal of devastation. Tunguska and Chelyabinsk were both close calls, and could have been very different stories had they had slightly different characteristics.

One thing to keep in mind, is that an impactor does not necessarily need to create a crater to cause significant damage on the ground, which also potentially a reason why the frequency of large and very large impacts may have been significantly underestimated.

For example, there is strong evidence for an impact at Köfels on 29 June 3123 BC (Julian calendar). A ~1 km sized asteroid is thought to have entered at an extremely low angle. Although it never made it do the ground, the radiant energy from the object would have caused the cloths on anyone caught outside at the time, to instantly burst into flame, and it is also thought to have caused a massive landslide.

One other thing to bear in mind is the Taurid meteor complex, and what are known as Swarm years.  In it's orbit around the Sun Earth crosses the Taurid meteor stream in two places, coinciding with November and June, and in swarm years Earth comes closer to where large fragments lurk. A large Taurid is largely accepted as the primary candidate for the 1908 Tunguska blast which leveled 10's of thousands of square km of trees, and also Chelyabinsk:  Taurid complex smoking gun: detection of cometary activity

[Mr Spock]

Given the coverage we have of NEOs a large scale ELE impact is unlikely. However there's the possibility of Tunguska scale events happening anywhere at any time. For all we know there may be billions of these size objects floating around the solar system. 

[Peter Drew]

I worry more about the MOT for my car.      🙂

[Leo S]

I don't loose any sleep over it (apart from staying up when it's clear and trying to image them), but I do think it's good to be aware that the threat exists. I often read reports where members of the public are shocked to have observed relatively small fireballs, let alone the mid-level events like Chelyabinsk.

Anyway, this thread was well timed. Today is the peak of the beta Taurids, and if not responsible directly, we know it is at least related to the Tunguska/Chelyabinsk impacts!

[John]

Having visited Meteor Crater a few years ago I would not want to be anywhere near when a largish chunk hits the ground 😲

Incidentally, it ought to really be called Meteorite Crater I think, as the thing that created it actually got to the surface.  

That hole was created by an iron chunk about 50 metres in diameter (pre-disintegration) they think.

[Leo S]

[maw lod qan]

Having recently seen NEO being spotted a few hours in advance of entering the atmosphere, along with very good prediction at where it would enter it, my question would be if one was seen coming  two hours away, would the public be informed?

Either way, one impacting a large city, or releasing mega tons of energy just above ground would be devastating. 

The panic would end up with the highways overwhelmed with traffic, making it possibly worse than keeping quiet an the picking up the pieces.

[900SL]

Wahba Crater in Saudi is quite something - approx 3 km across and 250m deep, fills the entire horizon if you stand near the edge.

There's some debate as to whether this was a meteorite or volcanic in origin. I favour volcanic, as the area has a number of old cinder cones and lava fields. Truly awesome place to visit regardless. It's a half day hike to the bottom and back. I wen there back in 2004, I think it's been touristified now.

 

 

[Zermelo]

17 hours ago, John said:

it ought to really be called Meteorite Crater I think, as the thing that created it actually got to the surface

... and quite emphatically, too.

I thought I understood the distinction, but this post caused me to check the IAA definitions. I was surprised to find that, while meteorite refers to the impacting object itself, meteor is a reference solely to the effects caused by passage through the atmosphere.

Further, while a meteorite is a body that reaches the ground, it actually becomes so named once it has gone dark, if that is sooner.

Also of interest is that the IAA defines a bolide as a meteor of a certain brightness, but to a geologist it is a body that causes an impact crater.

[Leo S]

On 25/06/2023 at 09:42, maw lod qan said:

Having recently seen NEO being spotted a few hours in advance of entering the atmosphere, along with very good prediction at where it would enter it, my question would be if one was seen coming  two hours away, would the public be informed?

Either way, one impacting a large city, or releasing mega tons of energy just above ground would be devastating. 

The panic would end up with the highways overwhelmed with traffic, making it possibly worse than keeping quiet an the picking up the pieces.

I don't think it would be possible to keep it under wraps, just because of the way it works, and because you can't stop others observing the sky. I would have thought that it takes at least 3 observations (if not more) to narrow it down/find out if it's on course for impact, and information is freely shared, so by the time it's known by one observer, others will also have access to the previous observations, and can make their own in order to narrow it down.

There is a silver lining though. People would only have to get to open ground and take shelter behind relatively weak obstacles to shield them from the radiated energy, and perhaps a more solid object for the following shock wave - obviously avoid glass/windows, and weak buildings if the blast is predicted to be close. That is assuming a smaller impactor like Tunguska and Chelyabinsk, which is the most likely worst case scenario. Of course, an impact on a populated area is very unlikely given that Earth's surface is mostly ocean and sparsely populated land.

As you say though, timings are usually tight. There may not be much warning - usually a few hours. 24-48 hours if you are very lucky, but more usually 4-8 hours. Not much time, but if people don't panic it should be enough for most to find safety.

It is interesting just how many are now being spotted just hours/days before/after close approach now - If you scroll down to the chart on https://spaceweather.com/  it's blatantly obvious how many of these objects approach and are only being discovered as they do so! (note the name of the object includes year of discovery).

 

[Leo S]

On 25/06/2023 at 11:26, 900SL said:

Wahba Crater in Saudi is quite something - approx 3 km across and 250m deep, fills the entire horizon if you stand near the edge.

There's some debate as to whether this was a meteorite or volcanic in origin. I favour volcanic, as the area has a number of old cinder cones and lava fields. Truly awesome place to visit regardless. It's a half day hike to the bottom and back. I wen there back in 2004, I think it's been touristified now.

 

 

Not an expert in craters, but sounds more volcanic to me. There are usually good indicators if they are meteoric origin, like spherules and isotopic ratios.

[Leo S]

On 25/06/2023 at 12:07, Zermelo said:

... and quite emphatically, too.

I thought I understood the distinction, but this post caused me to check the IAA definitions. I was surprised to find that, while meteorite refers to the impacting object itself, meteor is a reference solely to the effects caused by passage through the atmosphere.

Further, while a meteorite is a body that reaches the ground, it actually becomes so named once it has gone dark, if that is sooner.

Also of interest is that the IAA defines a bolide as a meteor of a certain brightness, but to a geologist it is a body that causes an impact crater.

Yep. So I'd usually say that a meteoroid (or asteroid/comet) is usually responsible for the luminous phenomenon we know as a meteor. At one time a meteor was anything (in the sky) that was not a star/planet or the Sun or Moon.

The word "bolide" does seem to have a different meaning to almost everyone, and perhaps is best avoided for that reason. Meteoriticists use it interchangeably between "a meteor that explodes" (could be almost any brightness), and "a meteor brighter than -14 mag." (if memory serves). Then there are superbolides like the recent event over the Kyiv/Ukraine that must have resulted in a brief spike in demand for clean underwear!

Edited June 26, 2023 by Leo S
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[Leo S]

I just came across another example, by complete chance, while googling the ""Atacama Desert" for another thread!

Around 12,000 years ago there is very strong evidence for an impact (air burst) in the region, but once again, no crater.

From the article:

"There may be lots of these blast scars out there, but until now we haven't had enough evidence to make us believe they were truly related to airburst events," Schultz said. "I think this site provides a template to help refine our impact models and will help to identify similar sites elsewhere."

 

[John]

19 hours ago, Leo S said:

I just came across another example, by complete chance, while googling the ""Atacama Desert" for another thread!

Around 12,000 years ago there is very strong evidence for an impact (air burst) in the region, but once again, no crater.

From the article:

"There may be lots of these blast scars out there, but until now we haven't had enough evidence to make us believe they were truly related to airburst events," Schultz said. "I think this site provides a template to help refine our impact models and will help to identify similar sites elsewhere."

 

That is interesting. The timing of the fall of the Vaca Muerta meteorite has been put at somewhere between 2,500 and 4,500 years ago. It is reckoned that nearly 4,000kg of material from that meteorite has been found over the years.

The Vaca Muerta fall did create some small craters:

 

 

[Leo S]

46 minutes ago, John said:

That is interesting. The timing of the fall of the Vaca Muerta meteorite has been put at somewhere between 2,500 and 4,500 years ago. It is reckoned that nearly 4,000kg of material from that meteorite has been found over the years.

The Vaca Muerta fall did create some small craters:

 

 

I hadn't heard of that fall till you mentioned it. These remote parts of the world always seem to get the larger impacts/falls. We don't really have anything like that here, apart from the recent Winchcombe fall perhaps, but that doesn't really have the same "impact" if you'll excuse the pun!

Incidentally, looks like there was another super-bolide, this time over central Europe last night. Quite a few reports added already - I'd imagine more to come, but it takes time to process them. The footage is worth a look too. Reminiscent of the recent predicted asteroid impact over N. France.

[900SL]

Also in Saudi, and coincidentally named the Wabhar Craters, way out in the Empty Quarter and a destination for the more hard core desert basher. 

Quote from Wiki:

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

 

The Wabar craters are impact craters located in Saudi Arabia first brought to the attention of Western scholars by British Arabist, explorer, writer and Colonial Office intelligence officer St John Philby, who discovered them while searching for the legendary city of Ubar in Arabia's Rub' al Khali ("Empty Quarter") in 1932.[1]

The vast desert wasteland of southern Saudi Arabia known as the Empty Quarter, or Rub' al Khali in Arabic, is one of the most desolate places on Earth. In 1932, Harry St John "Jack" Philby was hunting for a city named Ubar, that the Quran describes being destroyed by God for defying the Prophet Hud. Philby transliterated the name of the city as Wabar.

..Philby had heard of Bedouin legends of an area called Al Hadida ("place of iron" in Arabic) with ruins of ancient habitations, and also an area where a piece of iron the size of a camel had been found, and so organized an expedition to visit the site. After a month's journey through wastes so harsh that even some of the camels died, on 2 February 1932 Philby arrived at a patch of ground about a half a square kilometre in size, littered with chunks of white sandstone, black glass, and chunks of iron meteorite. Philby identified two large circular depressions partially filled with sand, and three other features that he identified as possible "submerged craters". He also mapped the area where the large iron block was reputed to have been found. Philby thought that the area was a volcano, and it was only after bringing back samples to the UK that the site was identified as that of a meteorite impact by Leonard James Spencer of the British Museum

...

Later in October 1966, a group headed by Aramco employee James Mandaville visited the site with heavy lifting equipment. They found two large uncovered meteorites. The largest, weighing 2,045 kilograms, had a pitted, but roughly level top surface about a metre (3.5 feet) in diameter with one end formed into a cone shape when the meteorite penetrated the atmosphere like a bullet; it was imbedded in sand, which had drifted over the top. It was photographed in situ, then overturned by a bulldozer and lifted on board a trailer where it and another, smaller meteorite were taken to Dhahran.[6]

[Leo S]

Relatively recent too by the sound of it. Also from the wiki link you posted above:

"Fission-track analysis of glass fragments by Storzer (1965) suggested the Wabar impact took place thousands of years ago, but delicate glass filigree, and the fact that the craters have been filled in considerably since Philby's 1932 visit, suggests their origin is much more recent. Thermoluminescence dating by Prescott et al. (2004)[9] suggests the impact site is less than 250 years old. This is consistent with Arab reports of a fireball passing over Riyadh, variously reported as occurring in 1863 or 1891 and heading southeast, reported in Philby's book Empty Quarter (1933)."

[Swoop1]

On 27/06/2023 at 19:57, 900SL said:

Also in Saudi, and coincidentally named the Wabhar Craters, way out in the Empty Quarter and a destination for the more hard core desert basher. 

Quote from Wiki:

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

 

The Wabar craters are impact craters located in Saudi Arabia first brought to the attention of Western scholars by British Arabist, explorer, writer and Colonial Office intelligence officer St John Philby, who discovered them while searching for the legendary city of Ubar in Arabia's Rub' al Khali ("Empty Quarter") in 1932.[1]

The vast desert wasteland of southern Saudi Arabia known as the Empty Quarter, or Rub' al Khali in Arabic, is one of the most desolate places on Earth. In 1932, Harry St John "Jack" Philby was hunting for a city named Ubar, that the Quran describes being destroyed by God for defying the Prophet Hud. Philby transliterated the name of the city as Wabar.

..Philby had heard of Bedouin legends of an area called Al Hadida ("place of iron" in Arabic) with ruins of ancient habitations, and also an area where a piece of iron the size of a camel had been found, and so organized an expedition to visit the site. After a month's journey through wastes so harsh that even some of the camels died, on 2 February 1932 Philby arrived at a patch of ground about a half a square kilometre in size, littered with chunks of white sandstone, black glass, and chunks of iron meteorite. Philby identified two large circular depressions partially filled with sand, and three other features that he identified as possible "submerged craters". He also mapped the area where the large iron block was reputed to have been found. Philby thought that the area was a volcano, and it was only after bringing back samples to the UK that the site was identified as that of a meteorite impact by Leonard James Spencer of the British Museum

Of historical note is the fact the St John Philby was the father of harold Adrian Russell "Kim" Philby, one of the group that spied fopr the USSR in the 40's and 50's

[900SL]

On 28/06/2023 at 02:38, Leo S said:

Relatively recent too by the sound of it. Also from the wiki link you posted above:

"Fission-track analysis of glass fragments by Storzer (1965) suggested the Wabar impact took place thousands of years ago, but delicate glass filigree, and the fact that the craters have been filled in considerably since Philby's 1932 visit, suggests their origin is much more recent. Thermoluminescence dating by Prescott et al. (2004)[9] suggests the impact site is less than 250 years old. This is consistent with Arab reports of a fireball passing over Riyadh, variously reported as occurring in 1863 or 1891 and heading southeast, reported in Philby's book Empty Quarter (1933)."

Philby's date has been pushed back a little, as there are written accounts of a fireball around 1700 which more closely matches the dating

Must have been spectacular to witness, it was estimated at ~15kT airburst. I did a lot of desert camping/photography in Saudi in Bortle 1-4 sites and sat through a few of the annual meteor showers

 

'The age of the impact craters was estimated by Storzer and Wagner (1977) at approximately 6400 yr, using fission tracks in impact melt droplets. Prescott et al. (2004) considered this age too old and redated impactite material with thermoluminescence (TL) dating methods at 290 ± 38 yr before present (corresponding to AD1714 ± 38) for the impact (ages ranging from 235 to 416 yr). Basurah (2003) correlated the Wabar impact event with the description, in two historic poems, of a bright fireball on September 1, 1704, observed in Tarim, Yemen (Fig. 1), 620 km SSW of Wabar. Reports that the fall occurred in 1863 are unsubstantiated, as discussed in Philby (1933a) and Prescott et al. (2004)'

https://onlinelibrary.wiley.com/doi/full/10.1111/maps.12218

 

[900SL]

Just now, Swoop1 said:

Of historical note is the fact the St John Philby was the father of harold Adrian Russell "Kim" Philby, one of the group that spied fopr the USSR in the 40's and 50's

Yes, Philby Senior led a 'boys own' life and had a lot of influence in KSA. I think I read a few years ago that he was instrumental in advancing US interests in the region, although I should check that.

Oddly enough one of Philby's grandkids was involved in a recent expedition to retrace the old mans trek.  I know Allan Morrissey, who leads the Riyadh Rovers and who joined the expedition as a regional expert

https://www.arabnews.com/node/2172681/saudi-arabia