Details Emerging On Tunguska Impact Crater 164
#space_on_irc.freenode.net (Dusty) writes "Lake Cheko in Siberia has been noted as the probable crater of the 1908 Siberian Tunguska event. This news was discussed here in December, but details on the crater were scant. Now a new paper written by Luca Gasperini, Enrico Bonatti, and Giuseppe Longo (the same team in Bologna, Italy that made news in December) has a horde of new details on the supposed crater. The team visited Lake Cheko complete with their own catamaran and completed ground-penetrating radar maps, side-scanning sonar images, aerial images, and some sample collection of Lake Cheko. Intriguingly, they also imaged an object under the sediment that may be a fragment of the impacting body. Their paper (PDF) includes a lot more details including images, side-scanning sonar image, a 3-D view of the lake, a morphobathymetric map. It's an interesting read, these dudes are good. They plan to return this summer and drill the core if weather permits, hopefully answering the question once and for all." The same team also has a more discursive article in the current Scientific American that includes some detail on the working conditions in the Siberian summer. Think: mosquitos.
Evidence against (Score:4, Informative)
http://abob.libs.uga.edu/bobk/tungmet.html [uga.edu]
For those that can't seem to find it (Score:5, Informative)
Not the original paper ... (Score:5, Informative)
The original paper by Gasperini et al. (2007) [blackwell-synergy.com] is also available as PDF and HTML [blackwell-synergy.com].
I'm not particularly convinced by the evidence they present. It's quite circumstantial. What they need to find and sample is an ejecta-related layer in the lake stratigraphy or in a lake nearby, and you'd think that if such a large impactor hit the ground there would be plenty of micrometeorite debris in the sediments of the surrounding area. Geomorphological evidence and age just isn't enough.
Re:Evidence against (Score:5, Informative)
1 Our sub-bottom acoustic reïection data show that, of a 10 m thick sediment pile, only the top
1 ± 0.5 m is laminated, ïne-grained, normal lacustrine sediments (Gasperini et al., 2007). The
lower chaotic material appears not to be deposited by normal lacustrine sedimentation.
2 210 Pb and 137 Cs datings on sediment cores from the lake suggest sedimentation rates of roughly 1cm/yr)1(Gasperini et al., 2001). Assuming this rate is mostly due to ïne-grained material transported into the lake from the Kimchu
River, the thin lacustrine sequence is compatible with a young (100 years) age for the lake.
Re:Evidence against (Score:2, Informative)
"we started our work at
Lake Cheko on the assumption that
it was older than the TE: our objective
was to find markers of the TE in the
lake's sediments. However, as our
study progressed, we began to question
the old age of the lake for the
following reasons:
1 Our sub-bottom acoustic reflection
data show that, of a 10 m thick
sediment pile, only the top 1 ± 0.5 m is laminated, finegrained,
"normal" lacustrine sediments
(Gasperini et al., 2007). The
lower chaotic material appears not
to be deposited by normal lacustrine
sedimentation."
they also give 2 more reasons: the sedementation rate for the above sediment gives an age of ~100years, and numerous personal accounts that never mention or map a lake at the location, only a swamp.
Re:For those that can't seem to find it (Score:5, Informative)
http://maps.google.com/maps?f=q&hl=en&geocode=&q=60.964,+101.86&ie=UTF8&ll=60.963631,101.859055&spn=0.010102,0.016522&t=h&z=16 [google.com]
Re:Not the original paper ... (Score:3, Informative)
Re:Semen Semenov? Ouch. (Score:3, Informative)
The name actually sounds more like Semyon Semyonov, pretty ordinary (except I wouldn't give my son a surname echo for a first name; matter of taste).
Could have been a comet (Score:4, Informative)
One side insists it was an Asteroid, but the material that would normally be present at an asteroid impact just isn't there. Others argue it was a comet, but analysis of comets in the last decade or so has put some real doubt into that theory as well.
At this point they pretty much have almost everything else worked out, from the velocity whatever it was had, where it traveled, where it likely went kaboom. They just don't know what the make-up of the object was. This report goes a long way towards proving exactly what the celestial object was.
Re:Very interesting article (Score:2, Informative)
Re: Mosquitos ++ (Score:3, Informative)
Russia is a relatively expensive country, but bicycle travel and camping is not that expensive. It is also a good way to experience a country since it brings you in out of the way places without as many tourists.