Wednesday, August 08, 2012

Siberia in the crosshairs

kw: book reviews, nonfiction, science, meteorites, craters

Take a look at Manicougan Crater in Quebec, 100 km (60 miles) in diameter and 214 million years old. It is one of hundreds of impact craters known; see the Impact Database.

I was hoping to find a nice image of a crater in Siberia, but none are this photogenic. The Popigai crater in north-central Siberia is the same size as Manicougan, but is only 35 million years old. Popigai is one of the places visited by Dr. Roy A. Gallant, and reported about in his book Meteorite Hunter: The Search for Siberian Meteorite Craters. Northern Siberia is a lot harder to reach than central Quebec.

Meteorite Hunter chronicles seven of Dr. Gallant's expeditions ("trips" is too tame a word), facilitated by his friend and colleague Katya, Ekaterina Rossovskaya, from 1992 to 2000. For the Popigai expedition, the number of researchers, family members, guides and staff numbered more than 25. The impact sites visited were Tunguska (of course!), Sikhote-Alin, Chinge, Pallas, Tsarev, Popigai and Teleutskoye. Four of these were meteorite falls in the Twentieth Century. Contrary to some reports, the Tunguska impact of 1908, really an aerial explosion, killed at least two people.

Any visit to Siberia is an ordeal. Crossing the continent via the Trans-Siberian Railroad is difficult enough, but getting to the geologically interesting locales requires vehicles that can manage deep bogs, cross rivers and climb boulder-strewn hills. A driver told the author that the best vehicle to use on Siberian roads is a helicopter. Indeed, three of the seven locations did require helicopter transport. Then I read that in 1992 the author was 68. Clearly, he has the endurance of a man half his age.

Dr. Gallant's interest is not simply geological. As he explains in his last chapter, Earth is still being pummeled by a rain of cosmic dust, pebbles and larger objects that amounts to between 40 and 60 tonnes daily, or 14,000-22,000 T/y. According to NASA's Near Earth Object program, an object 10 meters across or larger hits Earth about every ten years. Calculated another way, such an object passes inside the Moon's orbit every day. The Barringer Crater in Arizona, 1.2 km across, was excavated by a 50m metallic object. The most reliable estimate by Russian researchers is that the Tunguska object was about 156 meters in diameter, but it must have been stony or even a stone/ice combination.

The Google Maps Meteor Crater Viewer shows these known craters for North America:

A similar view for northern Asia and part of Europe:

The Mercator projection used exaggerates the size of Siberia, because it is so far north. Its area is about 15 million square km, while that of North America is 25 million. But the seeming sparseness of craters in Siberia just indicates how little explored it is, compared to North America and Europe. There are hundreds of craters yet to be found.

Among known craters, this list from Wikipedia is instructive:

This shows the eleven known craters, 20 km or greater in size, that are 65.17 million years of age or younger. It may be that the two oldest, Chicxulub and Boltysh, were simultaneous, though the Ukranian crater's size indicates it had less than 1% of the energy of the other. Then there is a cluster of three craters aged 35 million years, including Popigai. There was an extinction event at that time, though it wasn't quite as bad as the one 65 million years ago, the younger impacts having perhaps one-fourth the energy of the older ones. The youngest crater on the list, Karakul, is but 5 million years old. It is likely that continued study will turn up dozens to hundreds more craters in coming years, to help us better estimate our chances of getting wiped out. Doing something about it is another thing entirely.

Reading this book reminded me of reading the "dinosaur hunter" books by Roy Chapman Andrews, many years ago. The thrill of adventure is the same, as is the frank assessment of the difficulties encountered. Of course, getting around Siberia still requires the good will of Russian bureaucrats, and some of that was hard for Katya to earn. Fortunately, the people who aren't bureaucrats were very welcoming. But getting from somewhere like Moscow to a remote Siberian village mainly required braving abominable travel conditions, and biting insects that are unrivaled (I've encountered mosquitoes the size of horse flies in southern Kansas, but the Siberian ones must be even worse). And, you'd better love beet soup. Borscht is the common fare in most places. The author reports it is all well worth it. Lovely scenery, welcoming people, and amazing science to be done. There is much more yet to do.

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