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Location, Location, Location

Between the Oort cloud, the Kuiper Belt, various collections of asteroids and random rocks, over four billion years there are a great many potential impactors wandering about as any casual telescopic glance at the Moon will show. By most standards, Mercury and Venus have been pounded – and likely Mars as well. There would have to have been some really HUGE impacts at one time to account for the current motions of Venus and Uranus. Still, even though a great many rocks are in our orbital plane, more or less, the Earth moves pretty swiftly, and is a relative small target in all the vastness of space. Besides the mass (size and density) and velocity of the impactor it also matters when and where it strikes. As intrepid simulators of the Eltanin impact (2.5 million years ago between Chile and Antarctica) have discovered, a deepwater collision is significantly different from a dry land collision. Of course, there’s the immediate area damage (a crater) as well as pyroclastic flows, molten ejecta and so on for dozens or perhaps hundreds of miles from the crater, but the real game changer is planetary or at least hemispheric atmosphere alteration. It is clear that major (many VEI=5 and all VEI=6) volcanic eruptions can cause an impact on climate for several years. Many of the impacts listed below ejected far more debris into the stratosphere than even all-time all-star volcanic events like Toba. The problems highlighted below are lack of precise timings in when objects hit, and whether events were close enough in time to reinforce atmospheric trauma.

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Jewels and Joules

The technology for dating an impact crater has gotten better – what probably should be done is to recalibrate all the ages in a standard way at some point. Of interest is when major impacts might have been close in time. Specifically, in this case, Chesapeake Bay and Popigai. There is also what is probably an impressive impact crater offshore slightly north near Toms River New Jersey. More of about that next post. Part of the problem here is impactors failed to use MySpace to give a date, decade, millenium or much else when they arrived. If Chesapeake Bay and Popigai were 500,000 years apart that’s quite different than 5 days, 5 months or 5 years.

http://impact.ese.ic.ac.uk/ImpactEffects/ is recommended

Here’s a table of calculations for a high iron (4000 kilograms per cubic meter) “rock” 20 kilometers in diameter hitting Earth. [note: 20 km would be larger than any known impactor.] The columns are velocity (meters per second); energy in joules; crater diameter in miles assuming 15% of energy, cubic meters of rock ejected, melt thickness in meters and melt volume in cubic meters.

For reference, the Hiroshima atomic bomb explosion was about 67 times 10 to the 12. Depending on velocity, density and size as well as a few other factors, several thousand Hiroshimas at once.

 

 

 

 

It is not easy being recognized as a greater crater

Earth is a dynamic planet – continents merge, collide and split; polar ice caps and glaciers contract and expand; oceans ebb and flow. Then there are volcanic eruptions, asteroid impacts, and humans busily digging mines and paving parking lots. The largest impact craters discovered so far are shown below (diameter in kilometers; note Popigai outlined in red) are almost all are entirely on land, which likely means lots of large craters below the ocean surface. How long a deep water crater would be recognizable is a matter of lively debate. They are without doubt far more expensive to analyze.

The four asterisks are explained by the fine folks at the Earth Impact Database as follows:

‘This revised diameter is the best estimate for the collapsed transient crater diameter (rim-to-rim dimension). Our previous diameters cited maximum damage diameter estimates. There is considerable confusion in the literature regarding the definition of “diameter”. In the Earth Impact Database, we are striving to cite the collapsed transient crater value where possible. This can affect the order of size: for example, Sudbury’s maximum damage diameter is ~260 km (as defined by the outermost ring diameter), while that of Chicxulub is ~240 km. However, the rim-to-rim diameter of Sudbury is less than that of Chicxulub’s (130 versus 150 km, respectively).’

By any measure, Popigai is BIG. Can a planet our size suffer that kind of impact and not be profoundly changed?

 

 

 

Traces Left Behind

A ground-level view of part of Popigai after the spring melt. It is difficult to distinguish whether round or at least elliptical lakes are naturally that shape, remnants of a volcanic caldera or perhaps an impact structure. The decision needs a geological survey and usually drilling as well.

The sample above is brecchia – it will be thrown out of an explosion for miles. Usually, the pattern of brecchia fall will provide clear clues to where the center and what the shape of the impact was. These observations are more useful when the impact was off a current shoreline as opposed to completely landlocked like Popigai.

Because of its location and potential worth, as well as the general attitude toward science during the Stalin regime, despite U-2 flights and satellite reconaissance, it was not really understood in the US what was going on during the Cold War years. Just another labor camp in Siberia to kill people out of sight.

 

Some Popigai images

Image courtesy of the fine folks at the University of New Brunswick. Popigai is not especially dramatic here – it is the bluish (sunken) region amid the surrounding orange and yellow mountains.

Another false color image from directly above. Still not very stunning.

 

Russian SABLE continued

We are strict about naming our applications after antelopes, so no, our SABLE is NOT named for the famed fur-bearing mammal (Martes zibellina)  shown here before being made into a coat

known impact craters in Russia marked with red circles – of interest is Popigai.

We interrupt ruminations about ORIBI for another antelope, SABLE

A map of central Russia. Of interest is the area around 71 degrees 39 minutes north and 111 degrees 11 minutes east (red star inside the red box)