Remember that the blast wave from the main explosion does not immediately lose its momentum. It's still screaming towards the ground at supersonic speed. The momentum of the original impactor added to the blast wave would enhance the blast effects at the point where the wave is most directly pointed at the ground.

A lot of the models of mid-air explosions of great strength (i.e., nuclear explosions) have the fatal flaw of assuming the explosion occurs from, and expands outwards from, a single fixed, unmoving point. This is not the case when a meteor plowing in at hypersonic speeds explodes. Some analyses of the Tunguska event are now downgrading the actual size of that explosion after the effects of the momentum of the blast wave were taken into account.

-the other Doug

At least over the period observed, I only see rotation along a single axis. That would be somewhat rare, wouldn't it?

-the other Doug

There is likely a rather large "strewn field" where fragments of the meteor landed. I wonder if the Discovery Channel is in negotiation to film a segment or two of the series "Meteorite Men" in Siberia?

-the other Doug

Exactly the point I made. The multiple booms were sonic booms created by the fragments of the original impactor after the initial explosion.

-the other Doug

I think the first loud report may have been from the explosion itself. The continuing popping sounds were likely sonic booms created by the remaining relatively large pieces of the impactor as they flew on along the trajectory of the original bolide. The fact that the contrail splits into two distinct contrails for the length of it that was left during the fireball phase of the entry (i.e., when the original object exploded) shows that at least two streams of debris came out of the fireball and recombined into a single, more coherent stream after the fireball faded.

Of course, not all of the debris followed the main stream, lots of pieces big enough to cause sonic booms likely flew out in a multitude of different directions, and many to most of them would still be traveling at supersonic speeds.

-the other Doug

I've been finger-licking the various videos, and I'm struck by the better views of the actual explosion. There is a flash and a rapid expansion of what looks like a spherical fireball, a very slight dimming, and a second much brighter flash in which the fireball expands enormously. As the fireball quickly dissipates, you see what looks like a very thin cloud of dark smoke that outlines a sphere about the size of the first fireball flash, which itself dissipates (or is drawn into the contrail) in less than a second.

The only lasting effect of the fireball was the thickening of the contrail. But the second flash of the double flash definitely generated a huge fireball that dissipated extremely quickly.

I wonder if the fireball was made entirely of gasses or plasma? Or if any fragmental debris in the fireball was actually pulled back into the contrail by the extreme vacuum created in the wake of the impactor?

I admit, I cheated a little bit in studying the fireball -- I found a youtube video that runs the best angles of the bolide's descent in slow motion:

https://www.youtube.com/watch?v=gW6JVG1SP4c

-the other Doug

Oh, cool -- the JPL visualizations manager is showing DA14 on Eyes on the Solar System.

-the other Doug

FYI, NASA TV is running live coverage of the closest approach of DA14 2012 from JPL, with some live feeds from telescopes in Australia, where the asteroid is currently traversing the sky.

-the other Doug

I can certainly see how there was a pretty big explosion in the air, there is a rather extreme pulse of light and then the contrail sort of vanishes. But -- a 500 megaton explosion only 18 km up, over a populated town, and all we had from that was a bunch of broken glass? I mean, that's more powerful of an explosion than the Tsar Bomba, the largest thermonuclear explosion that has ever been accomplished, and that explosion caused the clouds to move at hundreds of miles an hour away from the blast at distances of 20 to 30 miles. I sure don't see that kind of immense airburst in the videos of the bolide....

-the other Doug


Edit:
oops -- just reviewed the figures, and either I misread the megatonnage the first time through or Mongo adjusted his figures. Still, a 5 MT bomb packs an awfully big punch...

The best of the videos I've seen show the contrail ending well above the ground, suggesting that the impactor disintegrated in the air. I'm wondering whether the bolide actually hit the ground, or whether the damage was caused by an over-pressure wave pushed ahead of it.

-the other Doug

I found another example of two apparent clasts or concretions on a little pedestal, just below where Little Italy is located, so I think we're looking at some process that left little pedestals.





-the other Doug

I think I'm going to refer to this unusual item as Italy, as it resembles a little booted foot (albeit upside-down).

Nick, I thought the same thing you did, that the shadow may just be a hollow. But on further examination, it truly looks like this is a positive-relief feature. It seems to cast a shadow that conforms to the boot-like shape. Look for the hammerhead-like shape at the end of the shadow...

-the other Doug

Quite excellent suggestion, Tom. Especially when you consider that Mars' atmosphere was losing pressure over the first billion years or so of the planet's evolution. Groundwater would become overpressured over time because of the lowering atmospheric pressure, and while our elegant equations can show the average loss of groundwater due to this increasing pressure gradient, we all know that the actual process takes place in bursts interspersed with periods of quietude.

I can imagine a situation where a groundwater reservoir is trapped by its enclosing rock beds, and some outside force (impact or other breaking or tearing force) creates a vent from the reservoir to the lower-pressured surface environment. A small vent would pull water up out of the reservoir over time, which would be pulled through cracks on the upside of the main crack(s) venting the reservoir. Thus forming clastic dikes.

The concept certainly has an aura of truthfulness to it.

-the other Doug

That puts some limits on the process of fracture fill, then, doesn't it? Low-end limits, in fact.

As I understand it, you can get fracture fill with a very small amount of water involved if the fractures being filled are very small; the water wicks up through the tiny cracks in a rock via capillary action.

If this material is filling voids up to three or four inches across, I can't see capillary action moving the water and its associated dissolved minerals up into a crack that size. That would almost require that the entire rock formation be completely immersed in liquid water, wouldn't it?

-the other Doug

We've been assuming that the white material is gypsum-like and that it was generated as a fracture-fill in an aqueous environment. However, the crushed rock from Snake River is entirely white on the inside.

Do we need to check our assumptions? At the door, or otherwise?

-the other Doug

Groannnnnnnnnnnnnn.....

-the other Doug

I guess I was thinking about the possibility of a calcium carbonate component to these rocks, which wet chem would quantify best. My understanding is that ChemCam and ChemMin would show the calcium component clearly, but not the carbon so much.

Please correct me if I'm wrong...

-the other Doug

Well, hmmm.... hydrated calcium sulphate is what makes up the light-colored vein fill, eh? And the Shaler unit, that shows the extensive cross-bedding, is said to be made up of grain sizes too coarse to have been emplaced by wind.

It talks like a duck, it walks like a duck, and it's quacking like a duck. I think we're on the verge of being able to state rather definitively that these rocks were created and carved by aqueous processes.

I guess the wet chemistry analyses will put the nail in the coffin. ***fingers crossed***

Drill, baby, drill!

-the other Doug

I'm not surprised we're seeing a DD here. The relative lack of them at Meridiani is, I think, due to the lack of pronounced hills and slopes in the area. DDs seem to spawn off of hills and out of very large craters. We have the kinds of slopes required to generate them at our current location, but haven't seen much in the way of hills up until now.

-the other Doug

As long as we're each saying what this new thin layer looks like to us, I'll say that, especially due to the choppy, raised waveform surface we see in some of it, this looks like a frozen mud flow that entrained small rocks and pebbles. Some of those rocks and pebbles have entirely disappeared, leaving holes and "bubble"-looking formations. Since this thin layer was originally emplaced, some of the entrained rocks and pebbles have completely disappeared and the voids they left have been infilled by some form of extruded material that we see filling cracks and voids. This extruded material looks very white in our images, and where it fills the voids there is a noticeable flow-like lineation pattern on its exposed surface that causes the dust that collects on adjacent material to only cling in the small cracks of the lineations.

I wonder -- what if some of the entrained "pebbles" were actually little chunks of either water ice or dry ice? The interaction between sublimating ice (water or CO2) and the entraining mud could explain the blown-bubble look of the indurated rinds around some of these little holes.

Just tossin' it out there...

-the other Doug

These "white holes" look like vesicles or empty clast sockets (more likely the latter) which have been partially infilled by the same white material that is filling the cracks in some of these rocks. In other words, both holes and cracks can be filled with the same intrusive material, and it looks to me like that's what has been happening here.

I'd guess the holes are empty clast sockets based on how bumpy this rock layer looks in more complete adjacent units. Looks like a clastic rock layer.

-the other Doug

Yep -- in fact, the earlier detail is where I began to think I saw a "capping" layer on the mound. The relative brightness of the top layer is not as obvious on the first of Ant's pans that you linked, but the effect of a rock layer that has sagged and then broken at the top, somewhat circumferentially, is rather strong there. The more nearly zero-phase image of the conical mound that I posted shows the top layer looking somewhat lighter toned than the rest of the mound.

Now, the albedo of the upper unit could just be bounced a bit due to preferential collection of bright atmospheric dust. But again, it reminds me a lot of the overall look of Von Braun out in Gusev.

-the other Doug

I'm fascinated by the conical mound in the near distance:



Looks at first glance a lot like Von Braun over near Spirit's final resting place. I even see a suggestion of a "cap" of a lighter-toned material on this mound.

-the other Doug

But... where's the kaboom? There was supposed to be an Earth-shattering kaboom!



-the other Doug

Yep, these look an awful lot like eroded clasts to me. What fascinates me even more then the bubblies, though, is the overall look of the terrain. I've seen undercut rocks like this many times, in both wet and dry streams here on Earth.

Here is a rather basic question -- the aerial views of this region appear to show alluvial features here. And the ground-based images show what strongly resemble water-cut rock overhangs. However, when we discuss surface rock erosion, it seems like you get Looked At Funny if you speak about the possibility of water erosion, as if suggesting that any close-in surface feature shows any remnant of water erosion just means you don't understand that Mars has been arid for billions of years.

If it looks like water erosion from above and from the surface, don't we have to at least give serious consideration to the possibility that at least some of the terrain we see around us is, in fact, the direct result of flowing water? Perhaps preserved for billions of years, but water-cut nonetheless? Sort of following the logic path of "if it looks like a duck and quacks like a duck, maybe it is a duck."

-the other Doug

p.s. -- I'm visiting family for the holidays, and the only way I really have of following the forum is via my Kindle Fire, and it's a longer process than normal trying to type with the on-screen keyboard, so I won't be posting a huge amount. Great for looking at the pictures, though.