[meteorite-list] Fireballs & Known Meteor Showers

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Sat, 17 Apr 2010 17:29:50 -0700 (MST)
Message-ID: <3c1d029a540cdb60b4fde4c401f577b6.squirrel_at_webmail.lpl.arizona.edu>

Hi Elton:

I do not know about spectra, but 3200 Phaethon (a Mercury-, Venus-,
Earth-, and Mars-crosser (gets to within 0.14 AU of the Sun) is the source
of the Geminids (December). But no coma has ever been seen (though was
supposedly a little brighter than predicted in 2009 when it had its last
perihelion passage).

The Quadrantids (Janusary) appear to be related to the asteroid 2003 EH1.
However, this may really be an extinct comet since it appears to have an
orbit similar to C/1490 Y1, a comet observed by the Chinese, etc. in 1490
(obviously).

Finally, there were the two asteroids that I mentioned in my prior email
about the two mid-April showers. Still not sure why they have been taken
out of the running for the Wisconsin fall).

Its good to sort of remember my presentation from years ago so I can track
some of this down of the Web!

Oh, I think from thermal models, that because comets spend most of their
time relatively far from the Sun, heating from their perihelion passages
does not get the interiors warm enough to melt any ice. Exterior ice (or
ice just below the surface) turns directly from solid to gas (which gives
us jets, etc.). Any interior heating would probably have to come from the
interior (radioactive decay or heat of formation). It is possible that if
you broke up a comet (and this does happen), that interior altered
minerals could be present, but, so far, no observational evidence of that
(but never say never)!

Just a little science (sorry), when a solid turns into a gas, it takes
energy and actually cools the surface (heat of sublimation). This is
something that most (all) of you have experienced in a similar way,
evaporation: evaporative coolers and the evaporation of sweat.

Larry

PS Sorry if I beat you to this again, Sterling. I will let you check out
any spectal connections (not sure where to start).

>
> I think there is a knowledge void which STARDUST would not have detected.
> There is a possibility of aqueous alteration during the transits close to
> the sun. As there are a lot of unmeasured variables to be explored, this
> will require much more thought regarding possibilities and consequences.
> We don't know the dynamics of how deeply and for how long a comet's
> interior might heat to melt its water stores- nor how many transits or how
> much if any altered minerals are eroded in those subsequent transits near
> the sun.
>
> One other point, Hasn't one meteor shower pair been attributed to an
> asteroid-like composition?? Spectra and speed suggested it was not a
> shower produced by a comet.
>
> Elton
> PS I seem to be unable to post to the list directly.? Too many yahoo
> bounces I guess
>
Received on Sat 17 Apr 2010 08:29:50 PM PDT