[meteorite-list] SMART-1 SMASHES

From: mark ford <markf_at_meteoritecentral.com>
Date: Mon Sep 4 05:08:20 2006
Message-ID: <6CE3EEEFE92F4B4085B0E086B2941B3159F915_at_s-southern01.s-southern.com>


I have another more mundane explanation of the 'square impact flash',
looking at the pixel structure of those pictures on the website, (the
image is a well compressed jpeg) they appear to have zoomed in on the
jpg to show up the flash in as much detail as poss (to the point at
which the jpg compression algorithm sqareifies the pixels), I suspect
that the image has essentially pixilated (i.e the flash is smaller than
the jpeg compression limit.

 I notice that if you tweak the image in a paint program the square
flash is the same size as the surrounding 'square jpeg blocks'.

Just one explanation, based on the pics I saw, the other is CCD elements
don't respond too well to very sudden changes in brightness and become
saturated with zoneing occurring around bright images - so could be an
artifact of the ccd chip they imaged it with.

Mark Ford

-----Original Message-----
From: meteorite-list-bounces_at_meteoritecentral.com
[mailto:meteorite-list-bounces_at_meteoritecentral.com] On Behalf Of
Sterling K. Webb
Sent: 03 September 2006 23:36
To: cynapse_at_charter.net; Meteorite List
Subject: Re: [meteorite-list] SMART-1 SMASHES

Hi, All,

    The space.com story says this (below) is an infrared image. There
apparently is no visual light image. Interestingly, the 0.001 second
flash is square, just like the spacecraft itself (SMART-1 is a cube
just under one meter in dimension). The flash covers a square
22-23 pixels by 22-23 pixels.

    The webpages for the CFHT say the "megacam" used on
this instrument has "a resolution of 0.187 arcsecond per pixel."
Assuming that's what was used for these photos, each pixel
would resolve about 0.3463 meter at the mean distance of the Moon,
and the observed flash would therefore cover a 7.6 to 8.0 meter

    Some of the things I find of interest: Despite being a very,
very low "grazing" impact, the flash is not elongated at all in
any direction. It's odd that the "corners" of the impactor are
so well represented, when you would expect a vaporizing impact,
necessary to create a crater, to be at least roughly spherical
despite the impactor's "square" shape. Craters are round (or
elliptical in the case of a grazing impact), not square, because
the energetic event is spherically uniform in force.

    Are the "corners" really diffraction spikes in the image? No.
The shape is quite different than diffraction spikes in the optics.
And the CFHT has no obstructions to cause them... Compare
the SMART impact image with this meteoroid impact on the Moon
observed May 2, 2006 (although a much bigger hit than SMART-1):

    Why square?

    Frankly, I can think of no way of creating a "square" flash of
light with an impact. But I can think of a "scenario" that could do
it. SMART-1 is an aluminum box one meter square. You can look
at the structure of the probe here:

    The bottom "deck" is lightened by eight triangular cut-outs that
outline its square shape. Assume that it was traveling "bottom down"
when it approached the lunar surface nearly horizontally (1 degree
incidence, they said). If the first contact was with the top of a rock
that projected a few meters above the surface of the Moon, it could
easily have ripped open the bottom, ruptured the hydrazine tanks,
and caused a hydrazine flash from INSIDE the square box structure
(which now has an open almost-square bottom) which would project
a square of light downward onto the otherwise unilluminated lunar
surface, producing a geometrically square ground flash.

    This whole sequence of events might only occupy 1 to 2 milliseconds.
After the 1 millisecond of illumination from inside the SMART-1 box,
the probe's box structure would be violently tumbling and gyrating from
the eccentric partial impact, ricocheting across the lunar surface from
irregular splat to the next, being ripped apart and leaving a trail of
and regolith gouges across the lunar landscape, instead of a crater.

    This explanation would imply that we will be unable to detect a
crater at the location (because there won't be one), so that's a kind
of test of the notion. It's also likely that the debris trail would
for some distance; SMART-1 was traveling at 1930 meters per
second at impact.

    Any other explanations of a "square" impact flash?

Sterling K. Webb
----- Original Message -----
From: "Darren Garrison" <cynapse_at_charter.net>
To: "Meteorite List" <meteorite-list_at_meteoritecentral.com>
Sent: Sunday, September 03, 2006 9:18 AM
Subject: Re: [meteorite-list] SMART-1 SMASHES


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