IPB

Welcome Guest ( Log In | Register )

40 Pages V  « < 35 36 37 38 39 > »   
Reply to this topicStart new topic
Mercury Flyby 1
dvandorn
post Feb 7 2008, 04:07 AM
Post #541


Senior Member
****

Group: Members
Posts: 3257
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



It occurs to me that the conditions during (and, especially, directly after) the most recent general resurfacing of Mercury could preserve crustal elasticity longer than you might expect. The earliest that resurfacing could have happened would have been right at the end of the LHB, I would think -- the current surface overlays what looks like lunar highland terrain, just covered in thick lava frosting... rolleyes.gif

IIRC, the Sun was a little hotter three and a half billion years ago than it is now. And Mercury lies so close to the Sun that even a robust outward heat flow would be reversed into an inward flow on Mercury's Sun-facing side.

During the long nights (assuming that Mercury's days weren't all that much different at the end of the LHB than they are now), you'd have outward heat flow and a general cooling of the crust. But the long days could have reversed the heatflow, adding a good percentage of the heat lost during the night back into the crust.

Under such circumstances, the crust could have remained fairly elastic for a rather long period of time, I would think. I'd also think that this might result in a greater degree of crustal differentiation than you see on the Moon or even Mars -- might that explain some of the very dark craters? Pockets of materials that were effectively sorted out of the crust to a certain depth, and then exhumed?

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Phil Stooke
post Feb 7 2008, 04:09 AM
Post #542


Senior Member
****

Group: Members
Posts: 5846
Joined: 5-April 05
From: Canada
Member No.: 227



I'm not sure about the rest of your argument, Doug, but the early sun was cooler, not hotter.

Phil


--------------------
... because the Solar System ain't gonna map itself.
Go to the top of the page
 
+Quote Post
dvandorn
post Feb 7 2008, 04:12 AM
Post #543


Senior Member
****

Group: Members
Posts: 3257
Joined: 9-February 04
From: Minneapolis, MN, USA
Member No.: 15



I guess I was thinking of the T-Tauri stage, which is supposed to be a pretty intensely hot period, sun-wise. But I suppose that happened earlier on, and is still a controversial theory...? rolleyes.gif

Seriously, thanks. I actually don't recall where I picked that supposed bit of information. Just goes to show that your brain can lie to you -- don't trust it!

-the other Doug


--------------------
“The trouble ain't that there is too many fools, but that the lightning ain't distributed right.” -Mark Twain
Go to the top of the page
 
+Quote Post
Juramike
post Feb 7 2008, 04:25 AM
Post #544


Senior Member
****

Group: Moderator
Posts: 2723
Joined: 10-November 06
From: Pasadena, CA
Member No.: 1345



QUOTE (Gladstoner @ Feb 6 2008, 09:58 PM) *
I assume a ring structure results from a stronger rebound, but how do varying properties of rock affect rebounding, not to mention the crater diameter?


Check out this freely available article showing impacts into solids of differing viscosity (this must've been fun to do!)
Fink, et al. Proc. Lunar Planet. Sci 12B (1981) 1649-1666. "Impact cratering experiments in Bingham materials and the morphology of craters on Mars and Ganymede".
Article freely available here.

(Lotsa cool diagrams and crater pictures - crater morphology (rings, rim heights, central peaks, ejecta splats) is dependent both on the velocity of the impactor and the viscosity of the impactee)

-Mike


--------------------
Some higher resolution images available at my photostream: http://www.flickr.com/photos/31678681@N07/
Go to the top of the page
 
+Quote Post
Bill Harris
post Feb 7 2008, 01:30 PM
Post #545


Senior Member
****

Group: Members
Posts: 2345
Joined: 30-October 04
Member No.: 105



QUOTE (dvandorn @ Feb 6 2008, 10:07 PM) *
It occurs to me that the conditions during (and, especially, directly after) the most recent general resurfacing of Mercury could preserve crustal elasticity longer than you might expect. The earliest that resurfacing could have happened would have been right at the end of the LHB, I would think...
<snip>
-the other Doug

Remember, early in it's development, Mercury supposedly collided with a planetesimal which stripped off most of it's silicate crust and left a core and mantle with a thin crust. This could have created a surface with atypical mechanical properties. I think that the (relatively) common double-ringed craters are due toi the material and not chance double-impacts.

In a way, the "mantle crust" condition on Mercury may be closer to the Earth's surface than any other rocky planet. With Earth's mantle convection (plate tectonics), the majority ocean basins are basaltic (AKA "sima") and the continental crust is granitic (AKA "sial").

--Bill


--------------------
Go to the top of the page
 
+Quote Post
ngunn
post Feb 7 2008, 02:00 PM
Post #546


Senior Member
****

Group: Members
Posts: 3205
Joined: 4-November 05
From: North Wales
Member No.: 542



NOVICE HAT ON
Can somebody here help with a couple of basic facts (or estimates) about Mercury's crust?
1/ What is its temperature, below the layer affected by diurnal variations?
2/ How deep are those variations thought to penetrate?
Can't really get my head round what might be going on without some idea on those points.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 7 2008, 06:25 PM
Post #547


Senior Member
****

Group: Members
Posts: 1574
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
bgarlick
post Feb 7 2008, 10:28 PM
Post #548


Junior Member
**

Group: Members
Posts: 53
Joined: 5-October 06
Member No.: 1227



If the large metal core of Mercury implies that it collided with another body in its past (and lost its upper mantle and crust), and our moon implies that a Mars sized object hit Earth and splashed off the moon, is it out of the ream of possibility that Mercury is the remnants of the impactor that hit Earth?

Did a 'Mars sized' planet strike Earth, splashing off the material that formed the Moon and then the remants (mostly the core of the original impactor) somehow settle into a tight orbit around the sun and is now known as Mercury?
Go to the top of the page
 
+Quote Post
JRehling
post Feb 7 2008, 10:48 PM
Post #549


Senior Member
****

Group: Members
Posts: 1574
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
ngunn
post Feb 8 2008, 08:57 AM
Post #550


Senior Member
****

Group: Members
Posts: 3205
Joined: 4-November 05
From: North Wales
Member No.: 542



QUOTE (JRehling @ Feb 7 2008, 06:25 PM) *
at the equator, the crust should be about 125C (surprisingly mild, eh?)


Unscientifically guessing from my own experience in caves, I suppose the variability is very slight more than 20 or so meters down.


Thanks for that JR. Surprisingly mild indeed.
On the second figure maybe Earth comparisons are misleading though, because of the big difference in day length.
Go to the top of the page
 
+Quote Post
john_s
post Feb 8 2008, 08:38 PM
Post #551


Member
***

Group: Members
Posts: 534
Joined: 3-December 04
From: Boulder, Colorado, USA
Member No.: 117



I get about 210 C for the sub-surface temperature near the equator, and about 120 C at 60 degree latitude- not quite so mild. The diurnal temperature variation will only persist a meter or so into the subsurface, because the dry, airless, regolith is extremely insulating.

John.

Go to the top of the page
 
+Quote Post
JRehling
post Feb 8 2008, 09:19 PM
Post #552


Senior Member
****

Group: Members
Posts: 1574
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
Holder of the Tw...
post Feb 8 2008, 10:41 PM
Post #553


Member
***

Group: Members
Posts: 395
Joined: 17-November 05
From: Oklahoma
Member No.: 557



Just wondering if maybe Io might have a few spots where the subsurface temp would be room temperature. Of course, such spots may be moveable and temporary.

Talk about every other factor being horribly wrong, some on Io would be downright ghastly.
Go to the top of the page
 
+Quote Post
JRehling
post Feb 8 2008, 10:49 PM
Post #554


Senior Member
****

Group: Members
Posts: 1574
Joined: 20-April 05
Member No.: 321



[...]
Go to the top of the page
 
+Quote Post
David
post Feb 9 2008, 03:59 AM
Post #555


Member
***

Group: Members
Posts: 809
Joined: 11-March 04
Member No.: 56



QUOTE (JRehling @ Feb 8 2008, 11:49 PM) *
It has to. Mostly, the surface is colder than Mars, but locally hot enough to melt rock. More likely isotherms surrounding caldera rather than "spots". But, yeah, good luck getting to those locations. That day spent in cruise between the orbits of Europa and Io will set up a real horrorshow before Io fills the window.


I have a very hard time imagining what it would be like on the surface of Io -- e.g., what would you be standing on if you landed? Or could you even stand up at all? I suppose a (rather sturdy) umbrella would be a good piece of apparatus to have...
Go to the top of the page
 
+Quote Post

40 Pages V  « < 35 36 37 38 39 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 21st December 2014 - 06:07 AM
RULES AND GUIDELINES
Please read the Forum Rules and Guidelines before posting.

IMAGE COPYRIGHT
Images posted on UnmannedSpaceflight.com may be copyrighted. Do not reproduce without permission. Read here for further information on space images and copyright.

OPINIONS AND MODERATION
Opinions expressed on UnmannedSpaceflight.com are those of the individual posters and do not necessarily reflect the opinions of UnmannedSpaceflight.com or The Planetary Society. The all-volunteer UnmannedSpaceflight.com moderation team is wholly independent of The Planetary Society. The Planetary Society has no influence over decisions made by the UnmannedSpaceflight.com moderators.
SUPPORT THE FORUM
Unmannedspaceflight.com is a project of the Planetary Society and is funded by donations from visitors and members. Help keep this forum up and running by contributing here.