[meteorite-list] Average size of craters across the solar system?

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Sun, 28 Jan 2007 22:41:40 -0600
Message-ID: <005e01c7435f$c5230830$ba50e146_at_ATARIENGINE>

Hi,

    The biggest craters are multi-ringed; they are
big enough that they are called "multi-ringed basins"
or just "basins." Properly, I suppose we should
call them "impact features" rather than craters.

    The Solar System Hit Parade: Record Holders
and All Basins Over 3000 km, are as follows:


Mars Elysium 4970 km*
Mars Utopia 4715 km*
Mars North Tharsis 4500 km*
Mars Chryse 4600 km*
Mars Hellas 4200 km
Callisto Valhalla 4000 km
Mercury Caloris 3700 km
Luna Procellarum 3200 km
              (* disputed interpretation)


    For bodies not on that list, the biggest crater is:

Ganymede Gilgamesh 550 km
Venus Mead 280 km
Io Pan 100 km
Europa Tyre 44 km
Titan "Unnamed" 440 km (Cassini radar)
Triton "Unnamed" 500 km (Voyager detection, not certain)
Earth Sudbury 250 km (?)
Earth Vredefort 300 km (?)

    From the lists, we can see first that bodies with
geologically active surfaces will only show the most
recent crater that hasn't been obliterated yet.

    We can see that the biggest craters are not on the
biggest bodies and that the bodies with the biggest
craters are not the closest to the Sun nor furthest from
the Sun.

    If we can draw conclusions, my guess would be that
the most important question after an impact would be:
"How Big Was the Truck That Hit You?" followed by
"How Many Big Trucks Drive Through This Neighborhood?"
Mars is close to the Asteroid Belt, perhaps too close. It
has played the odds too often and come up Snake Eyes
more times than is healthy for a young planet. Less certain
is that Luna, Callisto, and Mercury are all close to heavier
bodies which may have accelerated ("slingshot") an
impactor to a greater velocity than the target body alone
would have produced.

> ...shouldn't, for example, the average crater size on Mercury
> be bigger than the average crater size on the moon?

    That would take more statistics than I have on tap tonight,
but they look remarkably alike. An unlabeled photo of Mercury
might well be carelessly assumed to be the Moon, unless you
looked for Mercury's characteristic scarp wrinkles that the
Moon lacks. They're not that prominent; you might need a
magnifier if the photo is small scale. The Moon has more
basins over 2000 km than Mercury does.

    Just for fun, before we understood about plate tectonics
and thought that land only moved up and down, not back
and forth, it was widely believed that the Pacific Ocean was,
not an impact feature, but an "outpact" feature, the place
where the Moon spun off the Earth, leaving what would be
the largest "basin" in the Solar System (if it were true, that is).


Sterling K. Webb
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----- Original Message -----
From: <lebofsky at lpl.arizona.edu>
To: <cynapse at charter.net>
Cc: <meteorite-list at meteoritecentral.com>
Sent: Sunday, January 28, 2007 9:08 PM
Subject: Re: [meteorite-list] Average size of craters across the solar
system?


Hi Darren:

Lots of other factors going on:

Extra velocity caused by the gravity of the impacted body.

Composition of the surface being hit.

Composition/density (and thus mass) of the impactor.

Surface processes that will affect the loss of craters or their just
fading away.

At some point, with an old surface, you get saturation of craters, so
reach a certain limit on number and size of craters.

I am sure there are other things, but it has been a long day.

Larry

On Sun, January 28, 2007 5:47 pm, Darren Garrison wrote:
> I was just thinking about this, wondering if anyone has tried to compare
> average sizes of craters across bodies in the solar system? I was
> thinking along the lines that, since orbital velocity is higher the closer
> an object is to the sun, then there should be more "bang for the buck" for
> impactors. So, shouldn't for example, the average crater size on Mercury
> be bigger than the average crater size on the moon?
> ______________________________________________
Received on Sun 28 Jan 2007 11:41:40 PM PST