[meteorite-list] Mystery object in photo

From: Chris Peterson <clp_at_meteoritecentral.com>
Date: Tue Dec 7 20:29:28 2004
Message-ID: <0df001c4dcc5$58efe000$f551040a_at_bellatrix>

Ron-

I would argue that determining the angle of a fall from the sort of dent it
makes in a car is far from a precise science! To my own eye, the dent in the
Peekskill car appears to have been made by something striking largely from
above, not at any sort of shallow angle.

I have modeled Peekskill, and have enough faith in my math and programming
skills to believe it was not far from vertical- less than 25 degrees. The
Nakhla report appears to be describing the fireball, not the actual angle
any stone was observed to land. Smoke trails are not low altitude phenomena.

Having spent a good deal of my time over the last few years modeling the
atmospheric dynamics of fireballs, I'll stick by my comment that a fall
significantly far from the vertical is unlikely. It would require that the
object maintain its cosmic velocity to a very low height. That can certainly
happen, but is not common. The more massive the object, the more of its
original velocity it will carry to the end. Objects massing 10s of kilograms
or less, which drop below 3 km/s higher than 20 km, will not be able to
sustain enough forward velocity to hit the ground at a shallow angle.

Chris

*****************************************
Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


----- Original Message -----
From: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
To: "Meteorite Mailing List" <meteorite-list_at_meteoritecentral.com>
Cc: "Ron Baalke" <baalke_at_zagami.jpl.nasa.gov>
Sent: Tuesday, December 07, 2004 6:11 PM
Subject: Re: [meteorite-list] Mystery object in photo


> >
> > The Peekskill fall is not difficult to model. The recovered piece was
> > falling nearly vertically at the end. It traveled 50 km after the end of
> > ablation because at that point its path was nearly horizontal, and it
was
> > still at about 3 km/s. But that forward velocity was quickly lost to
> > atmospheric drag.
>
> No need to model, the Peekskill meteorite left a hole in the car trunk,
and
> the angle of that hole was definitely at a large angle away from vertical.
>
> > I don't know the details of the Nakhla fall, but I would be suspicious
of
> > witness reports giving 30 degrees from the horizontal. There is really
no
> > mechanism to explain how any ballistic object that has slowed to a few
km/s
> > while still 30 km or more high could have significant horizontal
velocity
> > when it reached the ground (unless it were falling in a hurricane!)
>
> Here's the entry angle of Nakhla as reported by John Ball in 1912:
>
> "The direction of approach of the object was from the northwest, and
> its track, marked by a column of white smoke, is said to have been
> inclined only some 30 degrees to the horizontal."
>
> Then there is the Neagan meteorite, which landed in Japan in 1995, and
also
> hit a car. The hole in the car created by the impact was analyzed,
> and the direction of the fall and impact angle were detemined.
> The Neagan meteorite hit the car at an angle of 40 degrees from the
> horizontal. You can see the report here:
>
> http://earth.s.kanazawa-u.ac.jp/ishiwata/labo/neagariUS.html
>
> So, Peekskill, Nakhla and Neagan are three examples of a meteorite not
landing
> vertically (straignt down).
>
> Ron Baalke
Received on Tue 07 Dec 2004 08:29:14 PM PST