[meteorite-list] SMART-1 SMASHES

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun Sep 3 18:36:07 2006
Message-ID: <004a01c6cfa9$53295c40$0b5ae146_at_ATARIENGINE>

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
square.

    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):
http://www.nasa.gov/vision/universe/solarsystem/13jun_lunarsporadic.html

    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:
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=31387

    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 one
irregular splat to the next, being ripped apart and leaving a trail of
debris
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 stretch
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


http://esamultimedia.esa.int/images/smart_1/observation_SMART-1_hawaii_H.jpg

http://www.esa.int/esaCP/SEM2N58ZMRE_index_0.html
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Received on Sun 03 Sep 2006 06:35:56 PM PDT