18 replies to this topic

[Veridian]

The most recent Scientific American Magazine (June 08) has an article on the 1908 Tunguska, Siberia impact. The authors of the article are Luca Gasperini, Enrico Bonatti, and Giuseppe Longo.

Mark J.D.

[csa/montana]

Mark, thanks for letting us know!

[Glassthrower]

Crud, I think my subscription just ran out last month.

[Dick Lipke]

Try their web site,I haven't seen anything yet but will keep looking.Google has tabs to access many astronomy and science web sites,Sci- amer. being one.I also get their magazine but usually see the story on the web site before I get it.

[Veridian]

The authors tell how they may have located a sizeable remnant of the asteroid/comet that created the Tunguska impact. This meter sized object is located at the bottom and near center of Lake Cheko and found when the team was mapping the contour of the bottom of the lake with acoustic-echo sounders. The data they have collected at this site, very near the epicenter of impact, in many ways points to the funnel shaped depression, which formed the lake, as being an impact crater dug out at that time. The object located with their equipment is buried beneath the sediment at the bottom center of this 'funnel'.

According to this article (as well as another story I had seen), the type of object creating the event remains a mystery, since numerous searches have not turned up any remnants located in the area. The team expects to follow up on this with a return mission to Lake Cheko later in the year.

Mike, start saving your money for a purchase.


Mark J.D.

[csa/montana]

Mike, start saving your money for a purchase.

Mike just went out & bought scuba gear

[Veridian]

Mike just went out & bought scuba gear [/quote]

********

Don't forget to take along mosquito repellent. The word is that they are rather fierce in those parts.

[Glassthrower]

Tunguska is an odd one.

Some factors come into play that will decide whether or not a meteorite is completely vaporized on impact.

Picture an automobile collision. Let's say the Earth is a car travelling 100mph down the highway. At this speed, anything that strikes the car (Earth) will do so with great violence - for example, say the car strikes a telephone pole. At 100mph, the car and the pole are going to be in terrible shape.

Now, imagine the telephone pole is travelling 100mph on it's own, travelling "head on" towards the car. The car and the pole meet, each travelling 100mph in opposite directions when a head-on collision takes place. The impact would be truly catastrophic for car and pole - both would be annihilated into tiny pieces.

When a meteorite, travelling at cosmic velocities (several miles per second) encounters Earth's atmosphere, the results can vary depending on the speed of meteorite (meteoroid) and it's direction of travel. Meteoroids that encounter Earth "head on" at higher velocities are more likely to produce a catastrophic result. Also, one other factor is the angle of penetration into Earth's atmosphere. A glancing shallow strike can result in the meteorite skipping off the top of Earth's atmosphere like a flat stone skipping on the surface of a pond. Sometimes they skip right off the atmosphere and keep going out into space. But sometimes a body will perfectly penetrate the atmosphere at a nearly vertical angle - this allows the object to encounter the least amount of atmosphere and braking.

In the case of Canyon Diablo, a large iron core of a stony asteroid struck Earth "head on" at great velocity and it encountered our atmosphere at almost 90-degree angle - puncturing it like a bullet. In this case, the meteorite was still travelling at cosmic velocity when it hit the ground. The resulting explosion was so violent, that it literally vaporized the iron body. Parts of it liquified and rained down on the Arizona desert as iron "spherules" or "spheroids" - molten iron rain. Some parts of the meteorite *did* survive - tiny tiny pieces, which we still collect and cherish today. But overall, the vast majority of Canyon Diablo meteorite simply VANISHED when it struck the Earth. The only reason a goodly amount survived is because the iron meteorite was hardy and robust.

Now, imagine a similar scenario as Canyon Diablo - but substitute the resilient iron meteorite with a friable mass of ice, regolith, carbon, and brittle stony matter. Such an object is typical of carbonaceous chondrites, howardites, and other meteorite types which are not nearly as resilient (and difficult to destroy) as solid iron. Such an object travelling at high cosmic velocities, punctures Earth's atmosphere at a "perfect" angle - and the violent impact completely vaporizes the meteorite. In such a case, very little, if anything, would be left of the impacting body.

Tagish Lake, a well-documented fall of a carbonaceaous chondrite C2-UNG (possible comet), weighed several dozen metric tons when it first hit the upper atmosphere. What remained after it hit the ground is only several kilograms of tiny fragments. Over 90% of Tagish Lake vaporized in the atmosphere on it's way down to Earth - because friable meteorite types rarely survive the fiery journey unless they are very large, and the circumstances of the fall/impact are favorable. (low cosmic velocity, less-steep penetration angle)

Alot of people over the years have invested time and money trying to find some remnant of Tunguska. The countryside around Tunguska is not conducive to finding meteorites and it's likely the Tunguska meteorite was a friable type. If so, it's not surprising that a main mass was never found. What is surprising, to me, is that it has taken this long for some evidence of the original meteorite to emerge.

If it turns out that a piece of the Tunguska meteorite is found - it may never end up on the collector's market. Many important meteorites "suffer" this fate - of being locked up in a state institution, forever out of the reach of collectors - like post-treaty Antarctic meteorites.

If some samples do make it onto the collector's market - expect the situation to be similar to Tagish Lake : the pieces available will be very tiny and very expensive. Tunguska could have the potential of being one of the most expensive/valuable meteorites in existence because of it's history - I'd predict it's value would exceed (gram for gram) some Martian or Lunar meteorites.

I'll have to look online for this story today - my curiosity is up now.

[edwincjones]

Let us all hope, including our credit card companies, that they find a big hunk of meteorite in the bottom of the lake.

Mike, I would like to order 1 or 2 mg

edj

[Dick Lipke]

I found it. Sci-Amer was mixed in with my "to read stack" I received last week,which includeds several astronomy,a couple science mags and Audubon,etc.etc.Beleive it or not one of my "to be read" mags had an article about in the future, radios small enough to fit in your hand and powered by batteries. I have way to many magazine subscriptions!

[Veridian]

Beleive it or not one of my "to be read" mags had an article about in the future, radios small enough to fit in your hand and powered by batteries. I have way to many magazine subscriptions! [/quote]


This is funny!

Just found some time to come in, have a look and read the last post in this thread. Glad I did.

Mark J.D.

[39.1N84.5W]

If it turns out that a piece of the Tunguska meteorite is found - it may never end up on the collector's market. Many important meteorites "suffer" this fate - of being locked up in a state institution, forever out of the reach of collectors - like post-treaty Antarctic meteorites.

Could you explain why the open market is a better place for these meteorites than a museum?

[Glassthrower]

I may have come across wrong here. I think all meteorites should be available for scientific study. As an obsessed collector, I'd like to have a small sample of every significant meteorite ever to strike Earth. A completely unrealistic goal I know, but the meteorites that are 100% locked away in museums/institutions are considered "holy grails" by the hardcore collectors. On rare occasions, museums and institutions will sell pieces to the public on a limited basis - usually through a respected auction house to the highest bidder. Such meteorites typically fetch astronomical prices because very little is on the open market. A meteorite could weigh 2 tons, but if only 1 gram is in private hands, and the rest sits untouchable in an institutional collection, then the value of that 1 gram is going to be extremely high. A meteorite that weighs 10 pounds, but over 8 pounds is floating around on the private market will have a lower value, typically, than the 2-ton specimen sitting in a museum. This is the opposite of what TKW (total weight and rarity) should dictate. And it's what makes pre-treaty Antarctic meteorites so valuable and desirable. And it's what makes meteorites like Ensisheim so valuable - besides it's historical value, precious little is available to private collectors. Most of it sits in a state museum in France. We collectors want what we cannot have. Isn't that the general rule of obsession?

Regards and clear falling skies,

MikeG

[39.1N84.5W]

Thanks for this perspective. I understand now.

[Dick Lipke]

It's best that these treasures"meteorites" end up in museums that are funded by the public,you and me,in return that means we are some what part owners of these magnificent beauties.A legacy that we can pass to all the children of many tomorrows to come.

[Glassthrower]

Thanks for this perspective. I understand now.

I'm just a space rock lunatic.

Every meteorite that goes into any display case other than my own is a BAD meteorite!

[pjstoker]

Chapters 15 and 16 of Richard Norton’s book “Rocks from Space” profile Harlow Nininger and Robert Haag. It was the commercial aspect of meteorite hunting that allowed both of them to find and recover so many meteorites. Samples from almost all of their finds eventually ended up in museums and universities for scientific study. Norton makes a good case for how the private collector/collections have contributed to the public collections and how both have complimented each other.

Pat

[Glassthrower]

Pat is right on the money here. Meteoritics is almost unique amongst the sciences. With the exception of amateur astronomy (double star, variable and planetary observations), there are very few areas of science where the amateur makes significant contributions. At first, amateur meteorite hunters were viewed with disdain by the orthodox scientific community. But then, the disdain became grudging (and eventually enthusiastic) acceptance. Without private meteorite hunters going out into the field to rescue specimens, many of the world's most interesting meteorites would have oxidized away or completely terrestrialized - lost to science forever. Let's face it, universities are not spending large sums of their budget to fly faculty and staff to the Sahara desert and Antarctica to look for specimens. This is also part of the reason why almost anyone can "walk in off the street" and join the Meteoritical Society (provided you can pay the steep cover charge) - a serious academic entity which publishes some very serious (and sometimes arcane) papers. Meteoritics is open to anyone who cares to join the field and indulge their space rock madness. I think all meteoriticists have "rocks on the brain" to some degree.

[Veridian]

A lot of good information here in this thread, Mike. You really have gotten into this and it certainly shows that there's been some homework on your behalf. Thank you for what you are doing!

Mark J.D.