Next Tunguska Expedition Background

Next Tunguska Expedition
Background
An important current scientific challenge is to acquire knowledge on cosmic impacts on our Planet. This knowledge could help in planning future strategies against extraterrestrial bodies threatening the Earth. The best-known historical cosmic impact took place in Siberia in 1908, the so-called “Tunguska Event”. On June 30, 1908 a huge explosion, equivalent to 1,000 Hiroshima nuclear bombs, devastated 2,000 square km of Siberian taiga close to the river Podkamennaya Tunguska, and an area sparsely populated by scattered groups of nomadic Evenk natives. This is what has been called the “Tunguska Event”, generally attributed to the explosion in the atmosphere of a cosmic body, either a meteorite or a comet (see the review: http://www-th.bo.infn.it/tunguska/Asteroids-Chapter-18.pdf ). However, after 100 years of studies, neither fragments of the cosmic body, nor impact craters have ever been identified in the Tunguska area.

We have conducted two expeditions and three short recognitions to the Tunguska site, and we have published a first set of papers on the results (http://www-th.bo.infn.it/tunguska/tu99public.htm ). We plan to return to Tunguska and carry out fieldwork aimed at testing the hypothesis that Lake Cheko, close to the epicentre of the 1908 explosion, might be a crater formed by the impact of a meter-size fragment of the cosmic body that survived the explosion.

An impact crater?
During a 1999 scientific expedition we found evidence suggesting that Lake Cheko, a small lake (500 m diameter; 50 m maximum depth) located 8 km NW of the inferred epicentre of the explosion, may be a crater left by a m-sized fragment of the cosmic body that survived disintegration. We published our results in Terra Nova: http://www-th.bo.infn.it/tunguska/terranova.html . Our papers have stimulated an intense scientific debate, as well as a diffuse interest in local media of many countries.

Some of the evidence in favour of an impact is: 1) the unusual, funnel-like morphology of the lake, different from that of common thermokarst Siberian lakes, but compatible with a “soft” low-velocity (<1 km/s) impact crater of a m-size projectile in a swampy ground with permafrost; 2) the lake appears to be not older than 1908, as suggested by radiometric dating of the lacustrine sediments and by the absence of aquatic plant pollens in sediments older than 1908; 3) a clear magnetic/density anomaly is present at the lake centre, about 10m below the bottom.

These data suggest that Lake Cheko formed in 1908 as a consequence of an impact, and that below its bottom we could find markers of the “impactor” that could tell us whether the Tunguska cosmic object was an asteroid or a comet. Our findings are in line with the ideas of Leonid Kulik, who first explored the devastated area. In fact, Kulik spent long a time searching for multiple craters left by the impact with the ground, possibly caused by fragments of a cosmic body that he believed was an asteroid. It is remarkable to see how his interpretation of the Tunguska Event could be re-evaluated after a century.
Expedition tasks
In order to test the hypothesis that Lake Cheko is an impact crater we will carry out the following operations:

1) drilling of the lake center, possibly to recover parts of the cosmic body, either fragments of an asteroid, or a geochemical signature left by a comet;

2) dense-spaced magnetometric/gravimetric survey of the lake bottom, that would allow us to estimate size and nature of the hypothetical buried object detected by our seismic reflection data below the lake bottom;

3) video inspection of the lake bottom, in order to confirm previous observations of tree remains, possibly from the forest devastated by the impact that formed the lake;

4) study of the trees that survived the explosion, found presently on the lakeshores: they should preserve an important record on the impact dynamics;

5) collection of rock samples from the region surrounding the lake. The study of these rocks will help in interpreting the mineralogy of the lake’s deposits;

6) assessment of lake’s chemistry and of CH₄ emissions.
The first task (to drill the lake bottom) is the more important and is crucial to solve the Tunguska mystery. It is also the more expensive and we cannot afford it without a generous sponsorship. In the meanwhile, we will send some of our researchers to perform the task 2-6 listed above (see http://www-th.bo.infn.it/tunguska/Tu2009.htm ).

Participants

Four research groups will participate in the Next Expedition: 1) lake drilling and video inspection, 2) georadar, 3) magnetometry, 4) dendrology and collection of wood and rock samples. A fifth group of divers-firemen will support the work on the lake and the construction of the base camp.

Logistics
We plan to start the Next Expedition as soon as the financial problems will be solved; building on the experience we gained in our 1999 expedition (see http://www-th.bo.infn.it/tunguska/99-photolist.htm ). The plan is to fly on an airplane from Italy to Central Siberia, then board a MI-26 helicopter that would fly us (30-35 persons) plus our equipment (~12 tons) to the Tunguska site. We would camp near the lake for about 15 days. Drilling will be done from a floating platform to be assembled in site. We have contacted various firms, both in Western Europe and in Russia, to organize the drilling operations up to a depth of ~100 m from the water surface.

International resonance

Results of the expedition will be published readily in scientific journals and normal press, and will be the subject of scientific documentaries. Different international broadcasting companies have offered to follow the expedition and to produce a film that will be widely distributed.

Left: 3-D reconstruction of the morphology of the Lake Cheko based on real topographic /bathymetric data.
Right: A possible itinerary for the Next Tunguska Expedition.