[X] My Assistant

[Phil Stooke]

Here's another slightly modified version of a press release image...



It's the lookback image with the area 'behind' the nucleus brightened a bit to show the full outline a bit better.

Looks like a tiny separate jet at upper left.

We really need as many views as possible from different directons to get a decent shape model. This plus the approach images are a start. There will be a bit of stereo during approach too. But I hope we will get more variation in these post-encounter images to help with the problem, either from rotation or changing view direction. And I am still hoping there will be a closer lookback image than this one!

Phil

[Guest_BruceMoomaw_*]

At the last press conference, it was specified by Peter Schultz that the impact movies show three different waves of ejected material. First, you see an extremely brief hemispherical wave of vaporized material from the initial impact; then a bright region that extends upwards into a tall column of ejecta blown almost straight up from the impact; then a separate cone-curtain of ejecta sprayed outwards at an angle. According to him, this is precisely what they expected from an impact into a very loose powdery surface -- the impactor drills down a short distance through that surface before exploding, at which point a column of ejecta is sprayed upwards through the entrance hole, and only then is a slanting curtain of ejecta thrown outwards for some time from the edge regions of the outwardly growing crater. The two separate shadows that Ed reports are apparently from the initial vertical column of ejecta and the later slanting conical curtain of it. They hope to be able to judge the precise angle of that slanting curtain from both stereo views of it and its shadow's orientation

[Guest_BruceMoomaw_*]

As for those circular, flat-bottomed but steep-edged "craters" seen on both Wld 2 and Tempel 1, I really don't think these are all that puzzling. They can be explained very well (as I said in my short piece on "Stardust "in the April 2004
"Astronomy") by the assumption that we have an initial small pit -- probably
a small impact crater -- which then grows as follows:

The combination of sublimating freshly exposed water ice and plain old
gravity explains it all. When the ice sublimates away from the shallowly
sloping floor parts of a bowl-shaped initial small impact crater, their lag
deposit of dust is going to just sit there without shifting (or fall back
onto the same places from which the sublimating water vapor blows it) -- and
in the process gradually build up a shield layer to inhibit further ice
sublimation from the floor. When ice sublimates away from the more steeply
sloping parts of the crater's walls, on the other hand, the dust that's left
behind IS going to slide downslope -- or get blown downslope by the water
vapor -- onto the crater's floor. And so the vertical slope of such walls
will remain high (and they'll recede horizontally away from the center of
the crater as more and more new ice is exposed by landslips of the
lag-deposit dust), while the depth of the crater floor, after its dust lag
deposit builds up to a certain thickness, will sink further downwards only
very slowly. Voila: growth of an initial small bowl-shaped impact crater
into a big, pancake-shaped depression which continues to grow steadily
sideways without increasing much in depth -- until such spreading
flat-floored depressions finally merge into each other and eat away the
comet's outer surface layer almost completely, leaving behind only a few
remaining "mesas" like those on the evolved surface of Borrelly. Then,
after that's finished, the process doesn't resume until some new small
impact craters are produced on the comet's new flat surface that are deep
enough to punch through its surface dust layer and expose some ice again.

The one possible problem with this -- as set forth by the Stardust team in
the "Science" article -- is that initial calculations suggest that Wild 2's
current foray into the inner Solar System, which had run only 25 years
before Stardust arrived, would not be enough to sublimate away more than
about a meter of its surface ice, and of course its depressions are much
deeper than that. However, they also point out that Wild 2 has been tossed
around by the giant planets enough that it may very well have undergone
earlier, longer-period forays into the inner System, each one ending when a
Jupiter flyby happened to redivert it back out into the outer System for a
while -- and those could have allowed the necessary deeper
sublimation-erosion to occur on its surface. Moreover, if there's one thing
Deep Impact proved beyond doubt, it's that exposed cometary ice sublimates
like hell -- maybe either because of lower-temperature ices mixed into the
water ice, or because we're seeing the conversion of some amorphous water
ice into crystalline ice by heat, which in turn releases some additional
heat to sustain and extend the process.

[Guest_BruceMoomaw_*]

And as for the possibility that Tempel 1 consists of several different KBOs that squished loosely together: this has long been thought to be the likely explanation for the strange "bowling pin" shape of Borrelly. We seem to be seeing what the planetesimals looked like in the earliest Solar System.

[dilo]

It's the lookback image with the area 'behind' the nucleus brightened a bit to show the full outline a bit better.

I elaborated same image in order to color-code plume (it appear a little bit defocused):


This is a combination of two frames taken from Impactor ("overexposed" negative PIA02126 + rescaled PIA02124):


Finally, cannot resist to make personal approach sequence (last magnification region is not sure, however):

[um3k]

Finally, cannot resist to make personal approach sequence (last magnification region is not sure, however):

The last region is, indeed, incorrect. Others have determined the correct location (as have I, independently), just look around the forum to find them.

[alan]

They are in trouble now

-----------------------------------)
The People of Ziquikcikty )
(also known as Comet Tempel-1); )
A class, seeking )
certification as such; )
Plaintiffs )
)
v. )
)
Michael A'Hearn, )
Rick Grammier, )
Alphonso Diaz, )
Michael Griffin, )
Karl Rove, )
Andrew Card, )
Richard Cheney, )
George W. Bush, )
Does 1-100, )
and Does 101-600,000, )
1 et Prcpui 50 n 1 abrat 05135, )
Government of Bars and Stripes; )
Defendants ) FILED:
-----------------------------------) Minxktaquicky 43, Year Nipathatep
(July 3, 2005)


STATEMENT OF FACTS

1. The matter before the court regards loss of life and limb, injuries, mental anguish, and property damage suffered on the early morning of Minxktaquicky 43, Year Nipathatep (July 3, 2005) at or around Mong 54 (10:52 PM PST).

2. At or around that time, inhabitants of Ziquikcikty (Comet Tempel-1) were awoken by a large explosion. They awoke to find that a large segment of the surface of Ziquikcity had been destroyed by an unknown agent, leaving a large crater in the surface. Ejected debris caused serious damage to approximately half the surface of Ziquikcity, and minor damage to all remaining areas of the comet......

http://www.transterrestrial.com/archives/005451.html#005451

[Bob Shaw]

The combination of sublimating freshly exposed water ice and plain old
gravity explains it all.

Bruce:

I think you're right - but with a couple of caveats (very minor). I suspect we're also looking at Phobos-like chains of 'things' here and there, plus some effusive resurfacing. I thought 'Enceladus' at first, but the notion of multiple KBOs coming together obviously spells Mimas...

There's a clear analogue too with the Martian south polar landscape, and the evaporating CO2 pits.

Makes you wonder what Dawn is going to see!

Bob Shaw

[Bob Shaw]

I blame Bob Geldoff!

Attached thumbnail(s)

 

[Phil Stooke]

Bob... Miranda?

Phil

[Bob Shaw]

Bob... Miranda?

Phil

Phil:

Yes!

(sheepish grin)

Bob Shaw

[Guest_BruceMoomaw_*]

"The People of Ziquikcikty )
(also known as Comet Tempel-1); )
A class, seeking )
certification as such; )
Plaintiffs )"

Would they be willing to take Tom Cruise as recompense, or would that be regarded as an act of war?

[Bob Shaw]

"The People of Ziquikcikty )
(also known as Comet Tempel-1); )
A class, seeking )
certification as such; )
Plaintiffs )"

Would they be willing to take Tom Cruise as recompense, or would that be regarded as an act of war?

Bruce:

At least it'd be a short war!

Bob Shaw

[Guest_BruceMoomaw_*]

Regarding the peculiarly discontinuous nature of both Borrelly and Tempel 1, Peter Thomas' very useful paper from the new "Space Science Reviews" ( http://www.beltonspace.com/bsei_web_page_g000000.pdf ) suggests that there are three possible causes for it:

(1) Separate cometesimals that collided gently.

(2) A nucleus that was fragmented but whose pieces then recollided.

(3) A nucleus affected by the "comet splitting" phenomenon, which as they say is still poorly understood.

And, regarding my theory of what causes the steep-walled but flat-bottomed depressions on Wild and Tempel, one additional detail: the phenomenon which initiates the formation of steep walls suddenly meeting a flat floor may well be the angle of repose of the surface lag deposit of loose cometary dust -- which could be quite steep, on such a low-gravity world, if the grains of dust are even slightly sticky. Once you get the lag layer of dust sliding off the very steep upper slopes of a crater, but remaining where it is on the slopes that are shallower han the dust's angle of repose in that gravity, the two phenomena are going to become self-amplifying as dust sliding off the steeper slopes accumulates on the shallower floor slopes below and serves as a pressure seal against more ice sublimating from off that floor -- while the steep slopes will continue to sublimate and thus retreat away from the crater's center, dumping their residual dust on the depression's floor below them as they retreat.

By the way, after reading the DI team's official scientific justification for their mission ( http://www.beltonspace.com/bsei_web_page_g000002.pdf ), I remain puzzled as to why it was selected. Apparently the only things that can only be done by this type of mission is the analysis (to some degree) of the chemical composition and hardness of very deeply buried cometary ice.

[Guest_BruceMoomaw_*]

Christ. If Keith Cowing is to be believed, NASA is now cranking up to throw away another perfectly good spacecraft:

http://www.spaceref.com/news/viewnews.html?id=1041

This, really, is quite insane if true.