[meteorite-list] Maximum theoretical Earth impact velocity

From: Matson, Rob D. <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Mon, 14 Apr 2014 19:54:38 +0000
Message-ID: <4A4FA25E4DFE584AA580F4F069F9B4401CD55440_at_EMP-EXMR104.corp.leidos.com>

Hi Chris/Shawn/All,

There is obviously something squirrely going on in that generated orbit.
For one thing, look at the error bars on the velocity -- they cover all
possible velocities (and as Chris points out, impossible velocities as
well).

I do have a comment about the oft-quoted 72 km/sec value. It is derived
from the orbital velocity of the earth around the sun which averages
29.78 km/sec encountering a retrograde body at just below solar system
escape velocity, which is around 42.1 km/sec at the earth's average
distance from the sun. This gets you to 71.88 km/sec. However, earth's
maximum orbital velocity (which occurs at perihelion in early January
each year) is 30.29 km/sec. And solar system escape velocity at earth's
perihelion distance is 42.48 km/sec. So that increases the closing
velocity to 72.77 km/sec. However, this still isn't the theoretical
maximum closing velocity, since I haven't included the acceleration of
the intercepting body due to earth's gravity well.

At an initial closing speed of 72.77 km/sec, there isn't a lot of time
for the earth's gravity to act on the body before it hits the atmosphere,
so the velocity boost is much smaller than earth's escape velocity (11.2
km/sec). From conservation of energy considerations, it can be shown
that the square of the impact velocity is equal to the sum of the
squares of the escape velocity and the approach velocity. So:

Max impact velocity = SQRT(11.2^2 + 72.77^2) = 73.63 km/sec

So in January, it is certainly possible to have a meteor with a
velocity above 73 km/sec. Anything above 73.63 would require the object
to have either originated outside the Solar System, or (as Chris
mentioned) to have been involved in a slingshot encounter with
another planet prior to encountering earth.

--Rob

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com [mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Chris Peterson
Sent: Sunday, April 13, 2014 1:10 PM
To: meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] HUGE Meteor Sighting in Cottonwood AZ - Stats from fall

There is almost no possibility of a meteor having that speed. The maximum possible velocity a body in orbit around the Sun can encounter the Earth at is 72 km/s. Anything faster than that would exceed the solar escape velocity, implying either some sort of slingshot orbit or a body originating outside the Solar System. Only a few meteors have been observed with velocities above 72 km/s, and those only a bit more, and perhaps of questionable measurement. More are in radar data (small particles), but it has been called into question if these actually have the velocities being measured.

Suffice to say, last night's meteor showed the characteristics of a low to medium speed parent body- something between 11 km/s and say 40 km/s.

What is the source of the data you are using for your calculations?

Chris

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

On 4/13/2014 1:57 PM, shawnalan at meteoritefalls.com wrote:
> Hello Listers
>
> I found some info on the fall and here is some stats...
>
> vel 667.2 km/s beg 135.8 km end 40.8 km
>
> Now could a meteorite come from the Vel speed? I mean thats really
> fast 667.2km, or that could be a mistake, which I think it is? With
> the meteor ending at 40km there is a possibility there could be some
> stones on the ground. And after looking at the video I could see the
> meteor for around 4 seconds and at the end the meteor got brighter.
>
> more stats below...
>
> Shawn Alan
> IMCA 1633
> ebay store
> http://www.ebay.com/sch/imca1633nyc/m.html
> Meteoritefalls.com
>
>
> time 20140413 3.0738 hours
> lat 32 26 22.632 = 32.4396 deg
> lon 253 16 38.856 = 253.2775 deg
> ht 40.775 b -1.38207 7.62031 -17.37020 -7.68054
> alp 300.962 +/- 0.462 deg
> del 70.037 +/- 0.310 deg
> v_inf 667.240 +/- 977.292 km/s
> v_avg 667.240 +/- 977.292 km/s
>
> a -0.002 +/- 0.006 AU
> e 493.776 +/- 1444.978
> incl 85.761 +/- 3.793 deg
> omega 168.225 +/- 0.185 deg
> asc_node 22.922 +/- 0.000 deg
> v_g 667.102 +/- 977.428 km/s
> v_h 668.691 +/- 976.474 km/s
> alp_geo 301.065 +/- 0.482 deg
> del_geo 70.004 +/- 0.311 deg
> q_per 0.982 +/- 0.001 AU
> q_aph -0.986 +/- 0.011 AU
> lambda 30.964 +/- 1.513 deg
> beta 78.151 +/- 0.165 deg
> true anom 11.775 +/- 0.165 deg
>
> T_j hyp
Received on Mon 14 Apr 2014 03:54:38 PM PDT