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Mercury Flyby 2
elakdawalla
post Oct 8 2008, 03:58 PM
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Here's an updated version of my context map. The new WAC image doesn't quite overlap with the NAC from yesterday, but there is nice overlap with the WAC.

Attached Image


The large crater in the center of the mosaic is Boethius; the large one to the upper right is Polygnotus.

--Emily


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Greg Hullender
post Oct 8 2008, 04:41 PM
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In the "are we there yet" spirit, given that this flyby dropped the period of Messenger's orbit from 132 days to 116 days, Flyby #3 (almost a year away) will happen in just a bit more than three orbits. Remembering that the original orbit had exactly a one-year period, we sure have come a long way!

--Greg
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Phil Stooke
post Oct 8 2008, 04:47 PM
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Here's a reprojection of the smooth plains image. If this isn't a case of volcanic plains embaying the cratered terrain I'm a monkey's uncle.

Phil

Attached Image


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Phil Stooke
post Oct 8 2008, 05:01 PM
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... and another one of the northern limb. This kind of reprojection makes the limb images much easier to interpret.

Phil

Attached Image


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Juramike
post Oct 8 2008, 05:09 PM
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Is it just me or does almost every other "fresher" crater in Doug's combined image here seem to have a scarp bisecting the crater?

-Mike


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Ian R
post Oct 8 2008, 07:28 PM
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QUOTE (Phil Stooke @ Oct 8 2008, 05:47 PM) *
Here's a reprojection of the smooth plains image. If this isn't a case of volcanic plains embaying the cratered terrain I'm a monkey's uncle.


Wow - are those wrinkle ridges in that picture Phil? If so, does this indicate that this volcanic flow was more viscous than those we typically see on the Moon?


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Stu
post Oct 8 2008, 08:04 PM
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Mercury's starting to look a lot like one of Chesley Bonestell's Moon paintings... smile.gif


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nprev
post Oct 8 2008, 10:41 PM
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QUOTE (Juramike @ Oct 8 2008, 09:09 AM) *
Is it just me or does almost every other "fresher" crater in Doug's combined image here seem to have a scarp bisecting the crater?

-Mike


I don't think you're wrong.

Hmm. Makes you kind of wonder if the crust of Mercury may have extensive deep magma reservoirs above the Hermian equivalent of the Mohorovicic Discontinuity; too deep to produce vulcanism, but enough to cause slumping & shifting after a major impact.


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Greg Hullender
post Oct 9 2008, 04:48 AM
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QUOTE (Juramike @ Oct 8 2008, 09:09 AM) *
Is it just me or does almost every other "fresher" crater in Doug's combined image here seem to have a scarp bisecting the crater?

Well, we haven't actually seen a picture of you, so it's hard to be sure.

--Greg :-)
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Phil Stooke
post Oct 9 2008, 12:43 PM
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The Vivaldi release - showing that the same crater can be seen in both encounters with opposite lighting - and Juramike's post showing the big southern basin in a composite of two views - suggest that you can combine the views from these two encounters. It's possible but not perfect. Here is one hemisphere:

Attached Image


It works very well. Several craters along the terminator are visible in both views, and the combination of views looks roughly globe-like. The other side doesn't work so well:

Attached Image


It's not as symmetric as you might think. But it does give the idea. A proper Steve Albers-style reprojection would allow it to work properly. I'm only playing with Photoshop here.

Phil


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Phil Stooke
post Oct 9 2008, 03:45 PM
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And a quick peek at the new image of the rayed crater near the limb, reprojected. Looks like another one with bright material inside it.

Phil

Attached Image


(I really should try to get a bit of work done...)


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SFJCody
post Oct 9 2008, 04:44 PM
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Just as Mercury has 'hot poles' does it also have, perhaps 'impact poles'; areas which (owing to Mercury's orbital and rotational properties) are likely to receive slightly more and/or slightly higher velocity impacts than other places?
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Phil Stooke
post Oct 9 2008, 04:55 PM
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No, it doesn't.

Phil


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elakdawalla
post Oct 9 2008, 05:00 PM
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That question is ringing a bell. Wasn't there a new paper out recently saying that Mercury doesn't have impact poles, but Mars does preferentially have more impacts near the poles?

Today's two three image releases appear to be from NAC departure mosaic #3. Updated context map is attached.
Attached Image


Key:

Inbound:
blue squares = NAC approach mosaic

Outbound:
Yellow = WAC Departure mosaic #1
Blue = NAC Departure mosaic #1
Purple = NAC Departure mosaic #2
Blue-green = NAC Departure mosaic #3

--Emily
Reason for edit: Added the third image release from today to the context map.


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SFJCody
post Oct 9 2008, 05:03 PM
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QUOTE (Phil Stooke @ Oct 9 2008, 05:55 PM) *
No, it doesn't.

Phil


Why not? It is true that Mercury is not tidally locked, like the moon (which does have cratering asymmetry for that very reason*), but it does have that 3:2 spin-orbit resonance resulting in a notable insolation asymmetry. Maybe I should crunch some numbers and find out.


*
QUOTE
Recent work has re-opened the question of lunar
cratering asymmetries. Examination of the spatial
distribution of rayed (and thus likely young) craters
gave evidence for a higher density on the Moon's
leading hemisphere[5][6], with an amplitude 150%
that of the trailing hemisphere. This seems to be in
agreement with a simple dynamical estimate [7], given
that the Moon orbits the Earth at 1.0 km/sec and thus
sweeps up more impactors (capable of generating a
crater larger than a given diameter) on its leading than
trailing hemisphere. A recent numerical study [8] re-
examined the hypothesis of an increased nearside
crater production due to gravitational focusing by the
Earth. It concluded that on average, the cratering rate
is approximately a factor of four greater on the near
side than on the far side.

Lunar Cratering Asymmetries. J. Gallant and B. Gladman LPSC XXXVI
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