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what made all those holes? Part 2
By David Bryant
In 1908 a massive explosion laid waste to thirty square miles of Siberian pine forest near the Tungus River. Thousands of trees were felled around an obvious epicentre and many animals (and quite probably local tribesmen) were incinerated or killed by the blast. Strange night-glows in the sky persisted for several days, while witnesses reported a blinding light and shattering concussion. However, despite numerous expeditions to the region, no satisfactory explanation has been forthcoming.
A 2014 TV documentary followed the adventures of a group of international scientists as they investigated the Tunguska impact site in Siberia: each one had a pet theory:
• An asteroid or meteoric impact
• An encounter with a chunk of anti-matter
• The explosive release of trapped gases from the mantle
• Aliens sacrificing their spacecraft to save humanity (No: really!)
One might reflect on the strange fact that these highly-qualified science professionals held such a diverse range of theories to explain a single event! The explanation for this is surprisingly straight forward: there is absolutely no concrete evidence at the site to prove conclusively what caused the explosion!
Apart from the felled trees, the only tangible ‘evidence’ was found by a geophysicist who located eventually a small outcrop of sandstone: samples from this appeared to contain shocked quartz grains which, bizarrely, he claimed to be proof that an explosive release of mantle gases from beneath the Siberian Traps basalt layer had been responsible for the devastation! As many of you will know, shocked quartz is frequently encountered at the site of an extraterrestrial impact: in fact (along with shatter cones) such shocked grains are considered to be the ‘smoking gun’ of an impact crater.
Little need be said about the anti-matter and UFO theories: there is, as yet, no proof that anti-matter exists, except as necessary extra mass to provide the gravity needed to hold the Universe together! And no fragments of exotic or alien technology have been located in the region of the explosion.
The generally-held ‘establishment’ belief is that Tunguska – and all large crater-forming events – were the result of an asteroidal impact. Unfortunately, no proven meteoric material was – or has ever – been found at the site: no nickel-iron, nor chondrite fragments. Neither have they been found at any other major impact craters such as Tenoumer, Manicouagan and Roter Kamm. This is strange, since many small to medium-sized craters are sources of stony or iron meteorites: Wolf Creek, Barringer, Gebel Kamil and Henbury being good examples. Even the giant Chicxulub event left behind only micro-tektites and raised iridium levels around the globe.
So what did explode above Siberia in 1908? And what made all the really large craters on Earth (and many of the small ones too!)?
In February, 2013 (thanks to phone and dashboard cameras) we were all treated to grandstand views of an event that could easily have been a ‘second Tunguska’: a large object entered the atmosphere above Siberia before exploding over the city of Chelyabinsk.As soon as the images of the meteor trail appeared online and on TV, I was struck by the fact that it was pure white, rather than the more frequently observed smoky grey-brown. Soon, reports from Siberia revealed that, despite intensive searching, only small, rounded fully-crusted wholestones were being recovered. This was in sharp contrast to the estimated entry mass of over 10,000 tonnes. Furthermore, nothing extraterrestrial was discovered beneath the much-photographed circular hole in Lake Cherbarkul, merely an ancient algae-covered rock.
So what was the object that did all this damage? There could be only one explanation: a small cometary fragment.
Despite popular impressions, comets are neither rare nor harmless cosmic snowballs: out at the very edge of the Solar System, the Oort Cloud and Kuyper Belt hold trillions of them.
For reasons that are not fully understood, one will occasionally tumble out of its orbit, plunging down the gravitational slope towards the Sun. Some swing round the Sun on a parabolic path and return to the depths of space: others are captured and remain in elliptical orbits, gradually sublimating as they pass by the Sun.
Although the greater part of a comet’s mass is water ice, it should be remembered that a cubic metre of ice has a mass of nearly a tonne: even a smallish comet 500m across would build up a devastating amount of kinetic energy as it accelerated into the inner Solar System, with a mass of around 1.04 million tonnes and a velocity approaching 70km/sec. Their surfaces are coated with a regolith of the material they pass through on their passage: this often becomes the raw material for periodic meteor showers when a comet that has lost its ice crosses the Earth’s orbit.
So it is entirely possible that collisions with small comets are responsible for those problematic large craters with little or no solid evidence of the impactor: their regoliths would be vaporised, producing a ‘spike’ of Iridium in the rocks, but no significant debris field would remain, as would be the case with an asteroidal impact.
So why has my hypothesis not generally found favour? Could it be that the money and resources spent searching for potentially Earth-crossing asteroids would be better spent elsewhere: remember, aperiodic comets (such as ISON) can appear at any time with insufficient warning to mount any form of ‘Bruce Willis’ style mission!
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by David Bryant
Until July, 1969 the idea that genuine fragments of rock from the Moon would one day be available for scientific research would have seemed highly unlikely: the possibility that such material could be added at relatively low cost to an amateur collection would not have even been considered. Fifty years later, anyone can purchase a genuine (if tiny!) piece of lunar rock for as little as £20: several hundred kilos of such material is available online and from dealers (Caveat emptor! Not all ‘moon rocks’ on internet auction sites are genuine: the best sources are those that display membership logos of the IMCA. Even then’ it’s best to check the membership number on the IMCA website – there are always those who will add a fake logo to their auctions for enhanced credibility!)
Genuine moon rocks originate from three sources: two available to the general public, one (theoretically!) not. There are some intriguing mysteries and a good deal of controversy surrounding these sought-after mineral specimens.
The first lunaites were discovered in Antarctica in the early 1980s by American and Japanese expeditions. In the ensuing thirty years, a better knowledge of what features to look for has resulted in many others being recovered from Australia, North-west Africa, and Oman, bringing the total number of all known lunar meteorites to about 120. (See a previous article for an account of the discovery and identification of lunaites.)
Soviet Union ‘Luna 16’ probe Launched in September, 1970, Luna 16 was the first spacecraft to land on the Moon, collect samples of dust and rock, and return them to Earth. After collecting regolith samples from the Sea of Fertility, where it had Luna 16, was launched back into space 26 hours later. It returned to Earth, bringing back 101 grams of Moon rocks.
Amazingly, a tiny amount of this material has recently become available to collectors, albeit at mind-numbing cost! In December 1993, the auction house Sotheby’s sold a slide with three small lunar fragments from Luna 16 for $442,500.
The Apollo 11 and Apollo 17 Goodwill Moonrocks
Following the six successful American moon landings (1969 – 1972) the Nixon Administration gave a total of 270 samples of material brought back from the Moon to each US State and to 135 member-countries of the United Nations. Astonishingly, around 180 are unaccounted for and at least one was the subject of a private sale at a price of $5 million. This, the Honduran Apollo 17 Goodwill Moonrock, was the subject of a ‘sting’ operation to retrieve the missing Apollo samples. After lengthy legal deliberations, the rock was remounted and presented back to Honduras in 2004.
United States - Delaware, New Jersey International - Brazil, Canada, Cyprus, Ireland, Malta, Nicaragua, Romania, Spain, Sweden
Probably the most intriguing of these is the Irish Apollo 11 sample. This was housed in the country’s main observatory, at Dunsink, North Dublin. In October, 1977, an unexplained fire destroyed the library at the observatory: during the investigation and clean-up that followed, the Moonrock was apparently consigned to the nearby Finglas rubbish dump, where, presumably, it remains. There is, of course, another explanation: that someone stole the rock before setting the observatory on fire to cover his tracks and hide the theft....
Are lunar minerals unique to the Moon?
Sadly, the answer since 2011, is no! On examination of the 800 or so pounds of Apollo moonrocks, most of the material was found to be virtually identical to terrestrial anorthosites, basalts dunites and so on.
Three minerals, however, were identified as being unknown on Earth: armalcolite, pyroxferroite and tranquillityite.
Since 1972, however, each of these minerals have been discovered on Earth, the last being tranquillityite, which was found in six localities in the Pilbara region of Western Australia.
This, naturally, has provided ammunition for the ‘Apollo Conspiracy’ debate: however, chemical composition aside, there are other differences, the lack of any hydrated minerals being the most significant.
As a matter of fact, one last potential source of authentic moonrock – or, to be exact – lunar regolith does exist.
On his return to Earth, one of the two Apollo 15 Moonwalkers, Dave Scott, apparently found dust from the lunar surface inside his personal preference kit (PPK) This is a beta cloth bag that contained a few sentimental items that each moonwalker was allowed to take with him on the descent to the Moon. Some astronauts took photos of their families, others rings and some even Masonic regalia! Scott had (supposedly accidentally!) transferred dust from his EVA gloves to the bag. A german collectibles dealer obtained some of this material on pieces of adhesive tape and sold it from his website. I myself had an example and can confirm it exhibited the classic ‘orange marbles’ look of the lunar regolith samples from Apollo 15!
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By David Bryant
A recent TV documentary (of the somewhat over-dramatic variety!) sought to explain several recent – and very damaging - falls of ice. Arriving at high speed from cloudless skies, these have battered roofs, cars and aircraft. The conclusion of the program was that these were examples of ‘mega-hailstones’, poorly-understood phenomena, more usually called megacryometeors by the Scientific community.
Around 50 of these have been recorded so far this century, varying in mass from 0.5 kg to real giants such as a Brazilian example of over 50 kg: a specimen with a mass of 200kg was reportedly seen falling in Scotland in the nineteenth century!
Meteorologists on the documentary spent much of the program establishing a mechanism by which huge chunks of ice could form in the upper atmosphere, other than in the conventional nursery of the convection currents of a cumulo-nimbus cloud. As most people will be aware, the powerful updraughts inside such clouds (which are typically associated with thunderstorms) allow the formation of hailstones. These may gyrate inside the cloud, accumulating mass until they are too heavy to remain aloft: hailstones the size of golf balls are not that uncommon.
However, they generally display a layered cumulate structure similar to that of an onion, while megacryometeors do not.
At the time of writing, no generally accepted mechanism for generating and supporting such large masses in the upper atmosphere has been forthcoming, although some of the theories put forward seem credible at first glance.
That chunks of ice occasionally fall from aircraft is undeniable and may be placed in two separate categories. The first (of
which I have personal experience) is generated by the dumping of liquid waste from on-board lavatories. Some years ago a
local radio station invited me to interview a lady who had been struck on the arm while hanging out her laundry. On arrival,
I asked to see the object that had hit her: to my amazement, she opened her freezer and took out a polythene bag, inside which I saw a bluish lump of ice similar to that in the photo:
The lady was less than thrilled when I told her she’d been storing lavatory waste from an aircraft among her fish fingers and
frozen chips! It had an obvious smell of disinfectant, so I’m at a loss to know how the lady for one minute thought it was a
Of course, icing on the fuselage and wings of aircraft still poses a threat to aviation safety, and flying through Supercooled Large Droplet (SLD) conditions can generate chunks of ice: these could fall to the ground and cause damage, but would not, I feel, be confused with genuine extraterrestrial ice meteors that should show signs of flowlines and ablation.
So then: is it possible that ice meteors could reach the Earth from space and pass through the atmosphere to the ground?
An online search will quickly discover a good number of learned publications that appear to answer this question with a resounding ‘no’. The majority maintain that a vast initial mass of tens of thousands of tonnes would be required for a football-sized chunk to reach ground level. But is this necessarily the case? The assumption is that frictional ablation would melt away most of the object’s mass, but this ignores certain factors:
1) Objects entering the atmosphere from deep space may hit the Earth head-on, at a combined velocity of 220,000kph or more. But equally, they may ‘creep up’ on the Earth from behind, with a closing velocity of just a few thousand kph, reducing frictional heating by a huge amount
2) Our putative ice meteor would be at a temperature just a few degrees above absolute zero (-273 degrees C) Whilst the outer layers would indeed become extremely hot, they would slough off like the heat shield of a re-entering Apollo spacecraft, taking heat energy with them.
Moreover, like the tiles on the five Shuttle Orbiters, ice is a pretty poor conductor of heat, so that the interior could be expected to survive better than, say, a piece of rock or iron.
Assuming, then, that some of the ice that falls from the sky may indeed originate in space, two questions immediately occur:
Where would ice meteorites originate? The Solar System is full of water-ice: billions of tons make up most of the mass of each of the trillions of comets in the Oort Cloud and Kuyper Belt.
Additionally, the Asteroid Main Belt must hold thousands of captured objects from these remote regions: these, we know, are
occasionally deflected into the inner Solar System.
I have written elsewhere that it is my belief that the majority of large craters on the inner planets and their satellites are the result of cometary (rather than asteroidal) impacts:
certainly, recent research has shown that to be the case with the Gilf-el-Kebir in Egypt:
How could we prove an extraterrestrial origin?
The relative concentrations of two isotopes of oxygen (17O, and 18O ) is used to assign an origin to planetary and asteroidal
meteorites. Cometary water should display relative oxygen isotope concentrations different to that of terrestrial water.
At the time of writing, just a few megacryometeors have been tested: these have all had terrestrial ROICs. But the samples tested were just a tiny fraction of the numbers that fall on the Earth: it is unscientific to discount the possibility of ice
meteorites on such a small sample. Should a sample be found to have an exotic ROIC, it could then be examined for evidence of presolar grains, interplanetary dust and regalith fragments it had picked up during its wanderings in space.
In conclusion, I suggest there is a high probability that chunks of cometary ice do reach the Earth’s surface from time to time:
I have written this article in the hope that not all astronomers will continue to dismiss a possible extraterrestrial origin for these.
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By David Bryant
Every year in mid-August astronomers all over the world eagerly anticipate the Perseid Meteor Shower: some years the sky can be full of ‘shooting stars’, on others hardly a handful are seen.
This year was pretty good: I personally observed over sixty meteors in around two hours and even managed to photograph one as it passed close to the familiar ‘W’ shaped constellation, Cassiopeia:
As many of you will know (either from your own reading or my previous articles) meteors are the tracks made by small stony or nickel-iron grains glowing and burning up due to frictional heating as they enter the Earth’s atmosphere. The vast majority of these are smaller than an apple and do not survive their fiery passage to reach the Earth’s surface.
Just occasionally a larger object will make it to ground level: it is then called a meteorite.
The most abundant types of meteorite are:
• Stony meteorites. These are left over from the formation of the Solar System or come from the surface of other planets.
A couple of hundred meteorites (known as achondrites) are known to have been blasted from the surface of the Moon or Mars by meteorite or cometary impacts: about the same number originated in the same way on asteroids such as 4-Vesta.
•Stony irons. Pallasites and mesosiderites are thought to derive from the core-mantle layer of shattered planets, or from collisions between stony and nickel-iron bodies.
• Iron meteorites These may have either condensed directly within the Solar Nebula or be the cores of disrupted, differentiated planetissimals.
Some meteor showers, however, are associated with the return of debris from periodic comets to our region of the Solar System.Beyond the furthest reaches of the Solar System, at a distance between 5,000 to 100,000 AU, (1 Astronomical Unit = the distance from the Earth to the Sun: around 150 million kilometres) lies an encompassing shell of trillions of cometary nuclei: the Oort Cloud. Since their formation from the solar nebula or capture by the Sun, these objects have collected a regolith of carbonaceous material and dust particles.
For reasons not yet fully understood (but possibly associated with the gravitational influence of passing dwarf stars) the orbits of these bodies can be perturbed, causing them to tumble inwards towards the Sun. Should this occur, by the time an Oort Cloud object reached the inner Solar System it would be travelling at a velocity of one hundred thousand kilometres an hour and will have acquired an outer shell of rocky material.
Encountering the electromagnetic radiation and streams of particles from the Sun, the icy nucleus may develop a coma and tail, becoming visible from the Earth as a typical comet.
In common with the great majority of these objects, it may swing around the Sun and pass harmlessly back into deep space. Possibly, however, it will be captured and enter an elliptical orbit, becoming a periodic comet that makes regular returns to the inner Solar System. Eventually it will lose most of its mass through sublimation, leaving a cloud of stony debris that might give rise to a new meteor shower, should its orbit cross that of the Earth.
The recent investigation of Comet 67P/Churyumov–Gerasimenko by the twin probes Rosetta / Philae demonstrated what many meteoricists had long suspected: although comets are primarily composed of water-ice, their surface is a regolith composed of whatever debris they have passed through during their adventures in space: it is this material that is responsible for periodic meteor showers like the Perseids in August (associated with Comet Swift-Tuttle), the Orionids in October (associated with Comet Halley) and the Leonids in November (associated with Comet 55P/Tempel-Tuttle)
Whenever a ‘good’ meteor shower (like those above) is due, the event is highlighted in the press and on TV. In the past there have been some incredible ‘meteor blizzards, like that in the old print below. Sadly, most years, non-astronomers are disappointed by the reality: even the one or two a minute I saw this August could not really be described as a spectacle.
Perhaps it is the publicity given to some showers or perhaps it is the antics of a couple of my American colleagues on TV making people more meteorite-aware, but after every Perseid Shower for the past four or five years I have received numbers of e-mails from people who think they have found one!
Here’s a recent example:
‘Hi! Is this a meteorite? I was watching out for meteors the other night when suddenly I noticed a black rock on the lawn: I’m certain it wasn’t there before!
I just went through the check list on your site: it is strongly magnetic, has a fusion crust, thumbprints, and there seems to be a widdsmanstatten pattern inside .I also clipped a little of edge and it is bright. I have added some pictures for you to look at. If it is a meteorite, I would be happy to offer it to you at the right price.’
Sad to say, I have no recollection of a single meteorite having been conclusively proven to have fallen during a periodic meteor shower. I should imagine the reasons are quite straight-forward:
• The size of particle that the Earth encounters when it passes through a field of cometary debris is quite small: probably the size of a grain of rice – far too small to reach the ground.
• The majority of periodic comets have visited the inner Solar System sufficiently often that most of the Earth-crossing debris has already been ‘hoovered up’.
• The trail of debris left by a comet is spread very thinly along its entire orbit around the Sun: the tiny region of the orbit of Halley’s Comet that the Earth crosses each year must statistically contain very few large chunks.
• The chances of anyone being fortunate enough to see one of these hit the ground and locate it are about the same as winning the lottery every week for a year!
In conclusion, the vast majority of meteoric material that arrives on Earth (about 300 tonnes a day!) is not of cometary origin: any that is will generally be far too small to reach the surface or be discovered.
If you’re interested in finding out more about comets, meteorites and their occasional impacts on our planet, my third book ‘Danger from the Skies’ is now available on Amazon or from my sales page:
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planetary craters what made all those holes pt1
By David Bryant
It is a fact that every solid body within the Solar System is pock-marked by high-speed impact craters: not just the four rocky planets Mercury, Venus, Earth and Mars and their moons, but also the satellites of the four gas giants Jupiter, Saturn Uranus & Neptune.
In addition, all the large asteroids that have been imaged from Earth or from space probes show similar dramatic evidence of past multiple impacts.
Currently, the most commonly-held belief is that the objects that created these structures were either large meteorites or small asteroids (accepting the definition that a meteorite is a chunk of metallic or rocky debris left over from the planetary formation phase or from the disruption of a planetissimal or asteroid).
For some time I have been reflecting upon the fact that very few of the meteorites I sell are associated with a known crater: some of course are:
• Barringer / Canyon Diablo, USA
• Wolf Creek, Australia
• Gebel Kamil, Egypt
But the vast majority of meteorites of all major types are found lying on the Earth’s surface:
there are no major craters associated with the huge Campo del Cielo or Sikhote Alin falls.
Furthermore, although there are around 175 large impact craters on Earth, none of those over 20km in diameter have produced meteorite finds! Strange!
A few, such as Chesapeake Bay, Gilf-el-Kebir, Darwin and Ries, have impact glasses associated with them, but wouldn’t you expect that an object large enough to create a hole 20km across would leave significant solid remains?
It has been estimated that the iron meteorite that created the Barringer Crater in Arizona had a mass of 63,000 tonnes: of this around 30 tonnes have been collected as large fragments (up to 639kg) while another 8,000 tonnes probably remain as fine particles in the crater walls and floor.
Rounding this up, we can suggest that about 12% of the impactor survived. Given that the Barringer Crater is quite small (around 1.2 km wide) then shouldn’t a really huge structure such as the 300 km Vredefort Crater have a vast strewn field of hundreds of thousands of tonnes of material scattered around it?
The usual reason given for the lack of such material is that the vast majority was vapourised on impact and dispersed over a wide area. But even if this were true, there should be some big lumps, albeit some distance from the crater. And have any nickel-iron deposits been found in association with a large astrobleme? (impact crater) Well just possibly yes!
Last year I had published an article in which I suggested that the huge Sudbury Ring structure was created by the impact of an asteroidal core that left behind the enormous reservoir of metallic minerals that is an important source of copper, nickel and iron.
I also gave several lectures on this theme and was astonished by the semi-hostile response I evoked!
To me this seems an eminently likely scenario: it is the only way to explain such huge deposits of dense elements at or near the surface. (You may remember from a previous article that it is axiomatic that, during the differentiation phase of planetary formation, such elements sink inwards to form planetary cores).
Some geologists have suggested that plumes rising from the core could bring heavy elements to the surface, but there is no credible mechanism for this!
Let’s sum up this, the first half of this two-part article:
• The Earth, like all rocky objects in the Solar System, shows numbers of structures produced by massive impacts throughout its history.
• Only a very small number of these craters have meteoritic material associated with them.
• There are just a couple of enormous astroblemes which are surrounded by rich deposits of metallic ores and minerals.
• The vast majority of craters must therefore have been produced by something other than meteoritic or asteroidal impacts I shall reveal my theory of their origin (which caused an Apollo Astronaut to change the content of his lecture!) in the next article!