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Stardust
Guest_exobioquest_*
post Jan 17 2006, 05:11 AM
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QUOTE (nprev @ Jan 16 2006, 04:29 PM)
I vote for P/Encke, since it's the purported source body for the August 10, 1972 daylight fireball that skipped back out of the atmosphere. BTW, I was under that thing in Western Montana at the time, if anybody is interested in an eyewitness account...awesome, but scary at that moment 'cause I thought it was an ICBM!


Dam, nprev how badly did it scare you?, did you crap your pants or take it with a more “Well no need to commit suicide now, the bomb going to do it for me” kind of stride?

By the way how do you know what’s in Stardust flight path… if that info in a link you provided already, sorry I’m lazy.
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nprev
post Jan 17 2006, 06:32 AM
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QUOTE (exobioquest @ Jan 16 2006, 10:11 PM)
Dam, nprev how badly did it scare you?, did you crap your pants or take it with a more “Well no need to commit suicide now, the bomb going to do it for me” kind of stride?

By the way how do you know what’s in Stardust flight path… if that info in a link you provided already, sorry I’m lazy.
*



It was something else. I was in Butte, MT at the time, nine years old. My younger brother & I were walking home in the early afternoon, and we heard this LOUD double sonic boom; shook the whole city. We looked up, and here's this white teardrop of a fireball hauling across the sky towards the north and leaving a long trail. My brother asked me what it was, and all I could think was that it was an incoming missile. So, we ran home & hid in the basement! laugh.gif laugh.gif laugh.gif

As it turns out, we weren't the only ones that thought that. NORAD originally interpreted it as a probable launch from a hostile submarine due to its odd vector (and the fact that it was heading pretty near Malmstrom AFB, MT), and began running the EWO (emergency war order) process...brrr. unsure.gif I think that event marked when NORAD got serious about tracking large meteors...

I also wonder what that would have rated on the Torino scale. If I remember correctly, the object was estimated to be around 100m in diameter, and the relative velocity was around 20 miles per second. Its closest approach was 35 miles above the Montana/Idaho border before it skipped back out of the atmosphere again.

So, I guess I can claim the dubious honor of being one of the few living people almost killed by an asteroid (or comet?) impact! tongue.gif 35 miles is a pretty close miss...

----

On a different note, as far as those targets I mentioned...I'm just talkin', I don't know if they're feasible or not. However, it looks like 3200 Phaethon probably won't work; its perihelion is well inside Mercury's orbit, and the aphelion is beyond Mars...sounds like too much differential velocity for an effective flyby, even if the geometry turned out to be favorable. sad.gif


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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
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edstrick
post Jan 17 2006, 09:18 AM
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The article on Space.com about a capsule return abort contingency, where the spacecraft would divert with the capsule and return in 3 or 3 1/2 years for another try suggests that Stardust may be close to a "free return" trajectory, much the same as was planned for Contour.

Basically, they have 2 options: Flyby of something within the post-swingby trajectory cone available using most of their propellant, whatever the best available target is, or put the vehicle on the Earth-swingby trajectory, and use the swingby to provide a much larger trajectory change and put it on a course to something more specifically interesting.

Regarding the 1972 fireball. I was in Yellowstone at the time with a brother and 2 friends on "the Great 1972 Western Trip".... a 20'ish day loop-vacation trip around the western US. No I <expletive deleted> didn't see the <expletive deleted> fireball. We were driving around Yellowstone making foul comments about tourists who'd cause "bear jams" by stopping in the middle of the road to take pictures and dodging spatter-showers. We heard about it the next day and made the appropriate comments of total frustration.
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edstrick
post Jan 17 2006, 09:29 AM
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Oh.. and I'd be quite surprised if the fireball was at all associated with a comet. That thing was undergoing significant ram-pressure force (it did make big sonic booms), and probably had to have had the mechanical strength of rock, at least.

There NEVER has been a meteor shower fireball that's reached low enough altitude to make sonic booms, and *** NEVER *** been one that dropped a meteorite.

A basic description of meteor material somebody made maybe 2 decades ago, and which holds up today, is that they have all the mechanical strength of cigarette ash. Small Kuiper-belt objects are probably giant cosmic dust-bunnies, loosely packed together, but ultimately made of clots and clumps of aggregates of sub-micrometer dust. Bigger ones in the many of kilometers size range may have had enough radio-isotope heat to melt or sinter ices and turn into a hard block of dirt-ice inside, but we've had little evidence anything we see as comets have had that much thermal processing.

Zdenek Sekaninana <sp?> some 15 years ago analyzed the Tunguska fireball's parent body's entry path and mechanical forces acting on it. The entry angle below the horizon is poorly constrained... some Zero to 15 degrees, which doesn't help modeling, but the object disintegrated and did it's airburst when it was being subjected to a ram-pressure enough to crush softish rock, plus-or-minus some amount. It was probably (if I remember right) stronger than the crumbly varieties of carbonaceous chondrite, but much softer than nickle-iron. Maybe an ordinary chondrite, maybe a less metamorphosed one.
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Decepticon
post Jan 17 2006, 01:49 PM
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I'm all for a all out Ceres flyby!



* Looks around room at Disbelief stares* huh.gif


biggrin.gif
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ElkGroveDan
post Jan 17 2006, 03:51 PM
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QUOTE (Decepticon @ Jan 17 2006, 01:49 PM)
I'm all for a all out Ceres flyby!
* Looks around room at Disbelief stares* huh.gif
biggrin.gif
*

Well since we are all dreaming, and this craft seems to have acquired some amazing capabilities, I'd prefer a flyby of Alpha Centauri. I'd also like a peek at the mass at the galactic center. biggrin.gif


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ljk4-1
post Jan 17 2006, 04:05 PM
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QUOTE (ElkGroveDan @ Jan 17 2006, 10:51 AM)
Well since we are all dreaming, and this craft seems to have acquired some amazing capabilities, I'd prefer a flyby of Alpha Centauri.  I'd also like a peek at the mass at the galactic center.  biggrin.gif
*


In Ithaca, NY, where Carl Sagan once lived and worked, there is an educational memorial to the man called the Sagan Planet Walk. The Sol system is scaled down to one mile, with informational monuments depicting the main worlds from our Sun to Pluto (the number of moons data is already terribly out of date for the Jovian planets).

The nearest star, Alpha Centauri (actually Proxima Centauri), would need a representative monument in Hawaii. And that is the nearest star to Sol.

http://sciencenter.org//saganpw/


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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djellison
post Jan 17 2006, 04:16 PM
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Realistically..... they'll look at the current spacecraft trajectory, and run forward to see what encounters are possible given the available dV and/or future flyby trajectory adjustments using Earth, and the power situation given how carefully they had to manage the spacecraft when it was out at aphelion.

It'll be a case of what can we visit with Stardust, not can we visit XXX with Stardust. Potential candidates will select themselves based on the orbital mechanics of it all.

Doug
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nprev
post Jan 18 2006, 01:45 AM
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QUOTE (edstrick @ Jan 17 2006, 02:29 AM)
Oh.. and I'd be quite surprised if the fireball was at all associated with a comet.  That thing was undergoing significant ram-pressure force (it did make big sonic booms), and probably had to have had the mechanical strength of rock, at least. 


*



I saw something about the 1972 fireball having a close orbital similarity to Encke in Sky & Telescope a long, long time ago...that info might have since been superseded. Still, if this is accurate, couldn't it have been a stony or iron/nickel mass that had been blown clear of the comet's nucleus by outgassing at some time? I'm not sure that we understand the structure of cometary nuclei well enough at this point to rule that out, or even to apply a "one-size-fits-all" standard to them as a class. Lots of variety observed in the nuclei we've examined to date...

Also, the diameter estimates for the object are in the 5-10m range now, not 100m as I originally wrote. Getting old now, so of course I exaggerate! laugh.gif


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nprev
post Jan 18 2006, 01:49 AM
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QUOTE (edstrick @ Jan 17 2006, 02:18 AM)
Regarding the 1972 fireball.  I was in Yellowstone at the time with a brother and 2 friends on "the Great 1972 Western Trip".... a 20'ish day loop-vacation trip around the western US.  No I <expletive deleted> didn't see the <expletive deleted> fireball.  We were driving around Yellowstone making foul comments about tourists who'd cause "bear jams" by stopping in the middle of the road to take pictures and dodging spatter-showers.  We heard about it the next day and made the appropriate comments of total frustration.
*


Sorry that you missed it, Ed...I just wish that I'd understood what it was at the time well enough to stay outside & watch it as long as I could! sad.gif

Actually, I just missed a small amount of feasible viewing; it was almost right at zenith when I heard the boom & looked up, and it was moving...it was probably over the northern horizon in less than twenty seconds.


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edstrick
post Jan 18 2006, 07:46 AM
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We really *don't* understand the structure of comet nucleii, but our best understanding is that the normal comet nucleus never really heated up inside enough to melt water ice, and the gravity is so low that they are "underdense" objects with a very high porosity level.

Indications of this is the fluffy-aggregate-of-submicrometer-grains nature of what we believe to be comet dust collected in the upper atmosphere, the ability of nucleii to totally dissipate into dust clouds, the mass (and with diameters roughly known, the density) of comets inferred from their orbital changes due to "non-gravitational-forces", and the lack of evidence for any meteorites or high-density metoroids from comet-associated meteor schowers. Hardly "rock-solid" evidence, but all pointing in the same direction.

That may totally not apply to mega-comets in the form of 100 or 200 or 500+ kilometer KB objects, or fragments of any formed by collissions. I have no idea what the modelling currently indicates is a size where Kb objects will squeese the porosity out of their cores, where they'll sinter cores into solid low-temperature ices plus water-ice and dust "cryo-rock", where the water itself will sinter solid, with low density ices driven out, where water will melt, or where in even larger objects you might get water driven entirely out of cores.

Add questions on the role of Aluminum-26 and other short-lived isotopes in heating small bodies like asteroids, and questions on the time scale of asteroid accretion vs KB object accretion... I don't know where the models have gotten to and what could be a minor part of the Earth-intersecting population from the outer solar system. But, so far, comet stuff seems to have all the "guts" of freeze-dried ice-cream.
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ljk4-1
post Jan 18 2006, 12:15 PM
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QUOTE (edstrick @ Jan 18 2006, 02:46 AM)
Add questions on the role of Aluminum-26 and other short-lived isotopes in heating small bodies like asteroids, and questions on the time scale of asteroid accretion vs KB object accretion... I don't know where the models have gotten to and what could be a minor part of the Earth-intersecting population from the outer solar system.  But, so far, comet stuff seems to have all the "guts" of freeze-dried ice-cream.
*


Interesting that your description of a comet compares it to ice cream:

"In honor and anticipation of humanity's first direct contact with a comet, folks at the nearby Cornell Dairy Bar created something special called Cornell Comet Swirl. A large poster in the room described this as a combination of "kaluha ice cream, dark fudge swirls, and swirls of creamy caramel and pecans."

"The poster continued that this confection "represent[ed] the fusion and cosmic swirling of a myriad of components," just like how scientists think comets are made up of a preserved celestial mix of ice, rock and complex organic molecules formed during the early days of our Solar System's creation. Comets may even have played an important role in the formation of Earth's atmosphere, oceans and life. This is why scientists wanted to sample a comet, to discover what was going on in our cosmic neighborhood five billion years ago."

http://www.zwire.com/site/news.cfm?newsid=...id=216620&rfi=6


--------------------
"After having some business dealings with men, I am occasionally chagrined,
and feel as if I had done some wrong, and it is hard to forget the ugly circumstance.
I see that such intercourse long continued would make one thoroughly prosaic, hard,
and coarse. But the longest intercourse with Nature, though in her rudest moods, does
not thus harden and make coarse. A hard, sensible man whom we liken to a rock is
indeed much harder than a rock. From hard, coarse, insensible men with whom I have
no sympathy, I go to commune with the rocks, whose hearts are comparatively soft."

- Henry David Thoreau, November 15, 1853

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Bob Shaw
post Jan 18 2006, 02:37 PM
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QUOTE (exobioquest @ Jan 16 2006, 03:59 AM)
nprev,

Yes, but I was not aware he was dead... may he spin in his grave, that all I going to say about him. (“if you can’t say anything nice, don’t say anything at all”)

Stardust could provide evidence for panspermia at a pre-biotic level, that is really exciting, but if Fred Hoyle theories turn out true I will publicly shove a broom stick up my…
*


An interesting review on Universe Today:

http://www.universetoday.com/am/publish/bo...rse.html?912006

I've always had a soft spot for Fred Hoyle (and Tommy Gold). They may have been wrong more often than they were right, but they were both *interesting*!

Oh, and some of Hoyle's theories *were* accepted, so when can we gather round to watch a certain broom stick's Star Trek moment ('To boldly go, where...')?


Bob Shaw


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Remember: Time Flies like the wind - but Fruit Flies like bananas!
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Guest_RGClark_*
post Jan 18 2006, 02:41 PM
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QUOTE (edstrick @ Jan 18 2006, 07:46 AM)
We really *don't* understand the structure of comet nucleii, but our best understanding is that the normal comet nucleus never really heated up inside enough to melt water ice, and the gravity is so low that they are "underdense" objects with a very high porosity level.
...



I prefer to call this the currently, generally accepted theory. The results from Deep Impact suggesting clays and carbonates in Tempel 1 haven't been published yet, but this is consistent with the aqueous minerals seen in carbonaceous meteorites.
This implies comets did undergo sufficient heating to form liquid water.


- Bob Clark
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djellison
post Jan 18 2006, 04:52 PM
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Anyone seen any images other than the two nasa-tv caps of the capsule since they opened it out. I'm a bit disapointed that we've not had any new pics etc.

There's a press conf scheduled for 1900 UT tomorrow, but that will clash with NH launch.

Doug
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