Mitchell Jones wrote:

Henry Spencer wrote:

In article <131cv77rno2im9c@corp.supernews.com>,
Hop David <hopd@cunews.info> wrote:

The smaller the comet, the greater the surface to volume ratio, and
the tinier the gravity. I believe a miniature comet would have a
miniature life span.
So I'm skeptical of Frank's theory.

Most everybody is skeptical of Frank's theory... to put it politely.
:-) The properties of his stealth snowballs need to be rather
:carefully
tuned -- and to show remarkably little natural variation -- to
escape all other forms of detection.

***{I don't have a strong opinion about this, but I think he makes a
pretty good case. Good enough, certainly, to shift the burden of proof
to his opponents. See http://smallcomets.physics.uiowa.edu/lecture/ for
the details. --MJ}***

For example, people have looked for them in archived Hubble images.
If there were really as many of them as Frank proposed, then some of
them should have crossed Hubble's field of view by chance... and
even highly nonreflective objects shouldn't have been completely
invisible to *those*
cameras. Yet none were found.

***{An object moving across Hubble's line of sight at several miles/sec
is obviously not going to produce an image. The exposure time would be
too small. The telescope would have to be located on the nightside of
the Earth to avoid dayside atmospheric glare, would have to catch the
small comet in the light just before it entered the Earth's shadow or
just after it emerged from it, and would have to swing in the prograde
direction at an appropriate rate, in order to keep it in view long
enough to achieve the needed exposure time. This method of telescope
usage is what Dr. Frank calls "skeet shooting mode." And when those
conditions have been met, the small comets were in fact detected. See
http://smallcomets.physics.uiowa.edu/lecture/lect8.html. --MJ}***

It doesn't bother me that Dr. Frank came up with a model of large comets
coated with a thin black hydrocarbon crust to explain the invisibility of
an anomaly in observations of something. It's the anomalies where
discoveries are made. The first model (theory) developed quite often
needs adjustments when further observations are made, or a total
different model (theory) proposed. Often, anomalies are overlooked,
ignored, dismissed for various reasons because it wasn't what the
observer expected. Also, if a new model or theory is proposed, it's
always in the realm of experience of the person proposing it. Explained
with the current understanding of that person or group.

If a better model or theory comes along to explain the anomaly, it's
probably simpler and leads to a better understand that leads to some
conclusions that can be test. To see if the new theory is correct.

In the Aerogel, the largest diameter impacts are the anomalous shallow
impacts with no discernable debris or dust. It's just the image of an
impact left in the glass. Really quite uninteresting to someone who has
set out to collect micrometeors or Cosmic Dust. They also explain away
the anomaly in terms they can understand, some sort of ultra high
velocity impact were everything is vaporized, dust and all. Anomaly
explained, now where are the particle that I'm interested in? Ultra high
velocity impacts creating the largest and most shallow craters in the
Aerogel?

***{You obviously haven't read the presentation on Dr. Frank's website.
If you had, you would realize that the probability of a small comet
impact with a satellite is extraordinarily low. By his calculation, we
would have one impact roughly every 50,000 years. That means the aerogel
doesn't show evidence of small comet impacts because there have been no
such impacts. (And if such an impact were to happen, the satellite and
the aerogel would be destroyed.) See
http://smallcomets.physics.uiowa.edu/faq.htmlx.

Let's do a very rough check of his number. Assume an average radius of
10 m for a small comet, and an average radius of 5 m for a satellite.
Treating the incoming small comets as point masses gives an average
target area of pi(10 + 5)^2 = 707 m^2. Assuming 600 operational
satellites (see http://en.wikipedia.org/wiki/Artificial_satellite) gives
a total target area of (707)(600) = 424,115 m^2 for each small comet
that passes through the region where the satellites are orbiting. The
spherical region from the center of the Earth up to geosynchronous orbit
has a cross-sectional area of pi(r^2) = pi(42,266,613)^2 = 5.6x10^15
m^2. Hence the probability that any single small comet will strike a
satellite is 424115/(5.6x10^15) = 7.56x10^-11. With 5 to 20 small comets
striking Earth every minute, let's take 12.5/minute as a representative
number. That gives 6,524,500 small comets per year. Thus the probability
per year that a satellite will be hit is (6524500)(7.56x10^-11) =
.00049, which means roughly one satellite will be hit every 2,000 years.

That's lower than Dr. Frank's number, probably because most satellites
have a radius closer to 1 meter than 5 meters, and because most orbit
below 800 miles. (Since small comets break up at 800 miles, I assume Dr.
Frank did not include lower-level satellites in his calculation.)
Despite being overly conservative, however, my rough estimate still
supports his his conclusion: small comets haven't affected any aerogel
experiments because none have hit any operational satellites yet (though
they may have hit some of the vastly more abundant space junk that that
is presently in orbit around the Earth).

--Mitchell Jones}***

No, impacts
with pristine low density Cosmic Snowflakes, much better explanation.

***{If you are talking about experiments done on the International Space
Station, with a perigee of 320 km, or about 200 miles, there would be no
small comets at that altitude: they break up at an altitude of about 800
miles. See http://smallcomets.physics.uiowa.edu/faq.htmlx. Thus they are
the likely source of the "low density cosmic snowflakes" you are talking
about. (Certainly a snowflake could not survive intact out in space: it
would sublime to gaseous form very quickly, and lose the ability to
leave an impact crater in anything, including aerogel.) --MJ}***

It's just possible that Frank found a real atmospheric phenomenon --
if memory serves, there was some mildly supportive evidence from
another group -- but nobody takes his proposed cause very seriously.

***{Why not take a look at his website, at the links given above, and
supply us with a point-by-point critique of his theory? I, for one,
would be very interested in such comments. --MJ}***

*****************************************************************
If I seem to be ignoring you, consider the possibility
that you are in my killfile. --MJ

lol, same here. ;-)

*****************************************************************
If I seem to be ignoring you, consider the possibility
that you are in my killfile. --MJ