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Caloris Basin and Antipodal Feature
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Caloris Basin and Antipodal Feature windbag 02-05-2008
Posted by windbag on February 5, 2008, 9:20 pm
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 Now that Mercury's great basin has turned out to be even larger than
assumed, more attention must be paid to questions about the origin of
such features.

Are we to believe that some ancient impacts have left perfectly round
holes; great circular pits, smoothly filling up again through some
inexplicably viscous "lava lake" process?

Is such a seemingly impossible infilling process common during early
planetary development; in a time of extra plasticity, before crusts
are fully baked in?

Perhaps other features -- such large, unfilled craters as Aristarchus
or the Hellas Basin -- hold an answer...

Posted by George on February 6, 2008, 1:27 am
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> Now that Mercury's great basin has turned out to be even larger than
> assumed, more attention must be paid to questions about the origin of
> such features.
>
> Are we to believe that some ancient impacts have left perfectly round
> holes; great circular pits, smoothly filling up again through some
> inexplicably viscous "lava lake" process?
>
> Is such a seemingly impossible infilling process common during early
> planetary development; in a time of extra plasticity, before crusts
> are fully baked in?
>
> Perhaps other features -- such large, unfilled craters as Aristarchus
> or the Hellas Basin -- hold an answer...

Umm, compared to Caloris, Aristarchus is puny.

George



Posted by robert casey on February 6, 2008, 3:52 pm
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windbag wrote:
> Now that Mercury's great basin has turned out to be even larger than
> assumed, more attention must be paid to questions about the origin of
> such features.
>
> Are we to believe that some ancient impacts have left perfectly round
> holes; great circular pits, smoothly filling up again through some
> inexplicably viscous "lava lake" process?

The amount of kinetic energy from the incoming object gets converted to
mostly heat when it hits. That might well be enough to melt the rock in
the area to make the lava.
>

Antipodal features come from sound shock waves from the big impact on
the other side of the planet. These tend to get focused on the
antipodal point of a sphere.

Something like that *might* have happened with the Earth got whacked by
that asteroid that hit the Yucatan peninsula 65 million years ago.
About that time in India, lots of volcanic activity, IIRC "Decan Traps",
happened and helped spew lots of pollution into the atmosphere. I don't
know if India was at the antipodal point from Yucatan, but it looks
fairly close (but about 30 degrees off) according to continental drift
maps I've seen. Of course, that map may be off by that much... That
would mean that these two events happened the same day back then. IIRC,
the measured dates of these two events overlap a little.

Posted by windbag on February 7, 2008, 12:13 am
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Aristarchus is small compared to surrounding lunar Mares, but still
important because, like Hellas, it isn't filled by glossily infilled
smoothness.

In reference to antipodes on Mars and the Moon (where they are
actually magnetospheres, as well) no laboratory recreation has been
made of such an incredibly geological effect.

Posted by robert casey on February 7, 2008, 1:23 am
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>
> In reference to antipodes on Mars and the Moon (where they are
> actually magnetospheres, as well) no laboratory recreation has been
> made of such an incredibly geological effect.

I doubt that magnetospheres have any effect here.

And it's kinda hard to fit an entire planet into the lab...

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