[meteorite-list] Stunning shot of mercury

From: lebofsky at lpl.arizona.edu <lebofsky_at_meteoritecentral.com>
Date: Wed, 8 Oct 2008 03:50:39 -0700 (MST)
Message-ID: <52040.71.226.60.25.1223463039.squirrel_at_timber.lpl.arizona.edu>

Hi Sterling and others:

1. There should be more stuff hitting Mercury and at higher velocities
than the Moon. This should lead to more craters and more craters with
rays.

2. This should also increase the weathering do to micrometeorite impacts,
overturning of the regolith, and higher solar flux.

3. However, it is thought that the weathering on the Moon is due to the
dispursion on nanophase iron in the Moon's surface material (darkening on
the rock over time). It is believed that there is less iron and titanium
in the surface rock on Mercury, hence the "weathering" does not darken the
rays (or at least a fast) as on the Moon.

Larry

On Tue, October 7, 2008 11:35 pm, Sterling K. Webb wrote:
> Hi,
>
>
> The interesting thing about the bright rayed craters is this:
> "...you'll see that almost all the bright small craters can be
> seen to have rays, too. Over time, the solar wind and meteorite impacts
> erase ray systems, so they come from young craters, and young craters tend
> to have brighter floors."
>
> Doesn't this imply a substantial population of NMA's?
> (That's Near Mercury Asteroids!) Or are they cometary
> impacts? This raises a question. There have been many searches for
> asteroids in intra-Mercurian orbits, quite thorough ones. Such an "inner"
> asteroid zone has been proposed by a number of astronomers, to account for
> numerous mistaken observations of intra-Mercurian "planets" and objects
> transiting the Sun. These searches have ruled out the existence any
> intra-Mercurian objects as large as or larger than 10 km, and it now
> widely believed that there aren't any inner system asteroids.
>
> So, what made these "recent" bright rayed craters on
> Mercury? The age of bright rayed craters on the Moon
> are thought to range from less than 800 million years to yesterday. Since
> it is the solar wind that erases ray systems and since the solar wind is
> much more intense at Mercury, these craters must be younger than 800
> million years.
>
> Is this evidence of a high cometary flux? Is this evidence
> of a now-depleted reservoir of inner system asteroids? Is this evidence of
> a "recent" inner system bombardment episode? (The surface of Venus is 480
> million years old, +/- 60 million years.)
>
>
> It's what I like about the Universe. Always something new.
>
>
>
> Sterling K. Webb
> ----------------------------------------------------------------------
> ----- Original Message -----
> From: "Darren Garrison" <cynapse at charter.net>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Wednesday, October 08, 2008 12:08 AM
> Subject: [meteorite-list] Stunning shot of mercury
>
>
>
> No, that isn't a particularly unwise order at a bar:
>
>
> http://blogs.discovermagazine.com/badastronomy/2008/10/07/watermelon-plan
> et/ ______________________________________________
> http://www.meteoritecentral.com
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>
> ______________________________________________
> http://www.meteoritecentral.com
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
>
>
Received on Wed 08 Oct 2008 06:50:39 AM PDT