(meteorobs) thoughts, please

meteors at eclipse.net meteors at eclipse.net
Sat Sep 16 12:58:58 EDT 2006


Until I can finish a full reply, here is some basic data.
While this is in response to a question about asteroids, the speeds also
refer to the atmosphereic interface at ~ 100 km for meteoroids.

As far as the violent displacement, sounds like hokum to me as meteor
paths reflect the incoming orbits, with no "violent" displacement. The
train is often deflected AFTER THE METEOR PASSAGE, creating twisting smoke
or ion trails. The meteoroid is not significantly deflected, though it
does decelerate. To affect the path of a meteoroid, unrealistec
accelerations would be required.

Meteoroids that are deflected, are first of all very large (otherwise they
burn up ) and approach at a very shallow angle to the atmosphere.

Copy of post regarding incoming asteroid speeds. Note, there were a few
minor refinements after this post, including a slight increase in maximum
pre atmospheric speed when the earth is at perihelion, but this is
basically correct.

""""Some Solar System basics.
The minimum speed of an impacting object (ignoring atmospheric
deceleration) is 11.2 kps(km per sec)=7 mps(miles per sec)=27,500mph(miles
per hour); i.e. the earth's escape velocity. This is for an object just
falling into the earths gravity well.
The earth does approx 30 kps=19 mps=67,500 mph in it's near circular orbit
around the sun.
The maximum speed for an object in solar orbit at 1 AU is 42 kps= 26 mps=
94,500 mph.
Therefore an object in a highly eccentric orbit catching up to us from
behind will be 16.4 kps= 10.2 mps= 37,000 mph. If it is in a retrograde
orbit and hits us head on (such as the Leonid's comet Temple-Tuttle or the
Perseid's Swift-Tuttle nearly do) it can be up to 72.9 kps=45.6 mps=
164,000 mph.
97% of the stuff in the solar system (especially an asteroid) is prograde
(travels around the sun in the same direction as the earth) but is not in
a near circular orbit, therefore it catches up to us from behind at some
angle as it moves past earth's orbit. Therfore the speed is at least
25,200 mph and can range up to the 45,000 you mentioned if it's in a more
eccentric orbit and does not catch up directly from behind but rather is
on it's way past us toward an orbit with perehelion inside the earth's
orbit.
Just for reference, since the earth's atmosphere (thick enough to
decelerate meteoroids or asteroids) is about
100 km=60 miles thick, you can see that even at minimum speed takes only
about 10 seconds to hit the ground if it comes in perpendicular. There's
not much time to decelerate, especially for a large object. For a head on
impact, the whole show is over in less than 2 seconds.
It's a good thing Leonids and Perseids are less than a centimeter in size
so they burn up before they reach the ground!! Of course there is almost
no upper limit for an object from outside the solar system, but these are
extremely rare. To my knowledge, no such object has ever been confirmed
that could not have been a solar system object within measurement error.
To determine the speed of a particular impactor (or meteor that does not
impact), if an accurate orbit can be determined the speed can be easily
calculated. If you ever see a fireball please determine where you are, the
path the object makes across the sky, how long it takes, and how long
afterward you hear any sound of explosion or sonic boom. Since sound
travels at 1 mile every 5 seconds, and an object that you observe can be
up to a hundred or more miles away this can be as long as 10 minutes!
--Meteor Wayne""""




> the following is quoted from an author of some standing, and some
> controversy.  for the latter reason, i choose not to identify the author
> for the moment.
>
> please consider the quote and advise any errors that you find.
> thank you
> dale botwin
> miami fl
> a..
>   1.. Meteors, after entering the terrestrial atmosphere at about 200 km.
> above the ground, are violently displaced toward the east. These
> displacements of the meteors are usually ascribed to winds blowing in
> the upper atmosphere.(24) The atmospheric pressure at a height of 45 km.
> is supposed to be but "a small fraction of one millimeter of mercury."
> (25) On the other hand, the velocity with which the meteors approach the
> earth is between 15 and 75 km. per second, on the average about 40 km.
> per second or over 140,000 km. per hour. If winds of 150 km. per hour
> velocity were permanently blowing at the height where the meteors become
> visible, it would not be possible for such winds of rarefied atmosphere
> to visibly deflect stones falling at the rate of 140,000 km. per hour.
>   2..
>   3.. Approaching the earth, the meteorites suddenly slow down and turn
> aside, and some are even repelled into space. "A few meteors give the
> appearance of penetrating into our atmosphere and then leaving it,
> ricocheting as it were." (26)
> ---
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