[meteorite-list] Rock on the ground or not?

From: Rob Matson <mojave_meteorites_at_meteoritecentral.com>
Date: Sun, 30 Mar 2008 18:15:15 -0700
Message-ID: <GOEDJOCBMMEHLEFDHGMMIEIGDIAA.mojave_meteorites_at_cox.net>

Hi Chris and Lasse,

There is another possibility to consider: Lasse may not have seen
a fireball at all. Consider:

1. So-called "point meteors" are very rare; they are rarer still
when the radiant is close to the observer's zenith.

2. The 10-second duration is probably too long for a point meteor
at such high elevation angle. Even at the slowest possible initial
entry velocity (11.2 km/sec), a meteor only 14 degrees from zenith
cannot maintain a velocity above 3 km/sec for that length of time.

I offer an alternate explanation: Lasse may have observed a
glinting satellite, perhaps an Iridium satellite. This is easy
enough to check, knowing the date, time and location of the
observation. On March 28th and 29th there were high elevation
Iridium flares for Sweden in the early evening in the eastern
sky -- in the vicinity of the bowl of the Big Dipper. --Rob

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com]On Behalf Of Chris
Peterson
Sent: Sunday, March 30, 2008 7:54 AM
To: meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] Rock on the ground or not?


Ah. So you're saying that you observed a stationary meteor, that didn't
appear to move across the sky at all? If so, that's the one special case
where you can accurately estimate the fall angle from a single
viewpoint. If the meteor's apparent altitude was +76?, then that is
indeed the fall angle (which is too steep to make this a promising
candidate for meteorite production).

Being so high in the sky also lets you narrow down both the distance and
the speed. The long duration suggests a slow speed, and a final height
of 30km would be a reasonable estimate. So that would place the end of
the meteor around 7km away from you, on the azimuth of the event. If
something survived, however, it would have continued to fall at a low
speed for several minutes, subject to the effects of the wind. Any
meteorites that landed could have been in any direction from the
retardation point, including behind it (that is, farther away from you).
If you have good wind information, you can make some rough estimates.

My own intuition is that the combination of steep descent angle and lack
of terminal explosion suggests that the meteoroid simply ablated away,
and probably didn't produce any meteorites.

Chris

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


----- Original Message -----
From: "Lasse Lindh" <3l at comhem.se>
To: <meteorite-list at meteoritecentral.com>
Sent: Sunday, March 30, 2008 8:34 AM
Subject: Re: [meteorite-list] Rock on the ground or not?


> Hi Chris
>
> Thanks for your answer. Well, this one pointed straight towards me.
> While bright and when it got weaker it did not move at all. I could
> see this because there were two stars just beside it. I am an amteur
> astronomer, so observing is nothing new to me. It did not deviate
> during the fall. I first thought it to be a GRB since it was so
> stationary, but then I realized that that was out of the question, so
> the only thing left was a meteorite. It showed no sign of break up.
> Checking the star map, it held an angle of 76 degrees. It's brightness
> could be a lot higher than -4. It's hard to tell.
>
> Regards
>
> Lasse
Received on Sun 30 Mar 2008 09:15:15 PM PDT