(meteorobs) Cloudbait. A difficult question to ask.

Chris Peterson clp at alumni.caltech.edu
Thu Jan 17 20:06:10 EST 2008


No, I don't see any relationship between sporadic fireballs and shower 
activity.

You need to consider that shower debris is orbiting the Sun. The 
velocity of a body orbiting the Sun is determined by the mass of the 
Sun, the distance of the body from the Sun, and the semimajor axis of 
the orbit. For a circular orbit at 1 AU, the orbital velocity is 29.8 
km/s. That's how fast the Earth is going. Orbital debris is almost 
always (probably always) in a fairly eccentric orbit where the semimajor 
axis will be greater than 1 AU, so when this debris crosses the Earth's 
orbit, it will be going faster than 29.8 km/s. All of the debris is in 
the same orbit, so except for tiny variations with respect to the 
orbital speed, nothing is going slower or faster. That's why there isn't 
much variation in entry speed for the members of any given shower. What 
variation there is comes from fairly minor effects such as the additive 
(or subtractive) component of Earth's rotation (under 1.5 km/s). Since 
the debris is co-orbital, collisions in the stream aren't going to 
substantially slow down or speed up any bodies.

The slowest body we could encounter would be something in a prograde, 
circular orbit at 1 AU- that is, nearly co-orbital with the Earth. It 
would be accelerated by Earth's gravity to escape velocity,  11 km/s. 
That's the slowest possible meteor. The fastest would be an object just 
below the Sun's escape velocity, 42 km/s, in a retrograde orbit, so our 
own velocity is added, giving 72 km/s (with some small correction for 
the Earth's gravitational effect, and its rotation).

Sporadic activity isn't random throughout the year. In fact, it 
currently peaks during the same half of the year that the northern 
hemisphere sees a peak in shower activity. This coincidence is, well, 
coincidental. It will change over time. But it may be what makes you 
look for a connection between sporadic fireballs and meteor debris 
streams.

Chris

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


----- Original Message ----- 
From: <stange34 at sbcglobal.net>
To: <meteorobs at meteorobs.org>
Sent: Thursday, January 17, 2008 1:48 AM
Subject: (meteorobs) Cloudbait. A difficult question to ask.


> Chris,
>
> In your opinion, does there seem to be many more large Fireballs 
> around the
> approximate times, or between times of  meteor shower activity, than 
> when no
> showers have been acive for awhile?
>
> I am referring to Fireballs that do not seem to have any relationship 
> to a
> radiant because of their apparent direction of travel.
>
> What I am leading up to is, as earth approaches a meteor stream in its
> orbit, most meteors have motion which can be traced back to a radiant.
> But......
>
> 1) If "some" rocks near the plane of the stream were moving very slow 
> when
> earth approaches, and......
>
> 2) If "some" other rocks IN the plane of the stream that were moving 
> very
> slow, were to be lightly struck by slightly faster rocks enough to 
> give it a
> mild new direction as earth approaches.......
>
> Could not earths orbital speed around the Sun of 67,000 MPH, Plus & 
> minus
> earths rotational speed of 1,000 MPH, be enough when earths atmosphere
> encounters these slow rocks to cause ablation by itself without 
> requiring
> these rocks to have any high velocity?
>
> Lastly then, could not many if not most of the so-called random 
> appearing
> directions of SPO's (& Fireballs),  really be slow or lightly diverted 
> rocks
> outside & within the stream and not random at all except in APPARENT
> direction caused by earths rotation and velocity alone?
>
> Big Fireballs seem to be scarce when it is long after a major shower.
>
> Had a hard time trying to word this clearly.
> Larry




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