Iapetus - Black on white or white on black? |
Iapetus - Black on white or white on black? |
Sep 14 2007, 07:40 AM
Post
#1
|
|
Member Group: Members Posts: 813 Joined: 8-February 04 From: Arabia Terra Member No.: 12 |
Seems to be a lot of dispute on this subject... I think it's ice from the interior, but what does everyone else think?
Edit: This world seems very complex so the question could perhaps be phrased as 'which of these options is most responsible for the Iapetan dichotomy?' |
|
|
Sep 16 2007, 10:41 AM
Post
#2
|
|
Senior Member Group: Members Posts: 2997 Joined: 30-October 04 Member No.: 105 |
You're right, Ed, this is all very mysterious. The answer may be billions of 5cm-tall Monoliths, or something odder.
Seriously: one thing I've noticed from the closest images. We've seen a few small, recent craters with white ejecta rays in the dark regions. But I haven't seen the opposite: dark, fresh craters on the light-toned regions. This leads me to suspect that the black is a thin dusting over the white, whereas the white is a thicker layer. I'm looking closely at the white-black-white contacts in the hi-res images for puzzle-pieces... --Bill -------------------- |
|
|
Sep 17 2007, 05:22 AM
Post
#3
|
|
Senior Member Group: Members Posts: 2530 Joined: 20-April 05 Member No.: 321 |
Seriously: one thing I've noticed from the closest images. We've seen a few small, recent craters with white ejecta rays in the dark regions. But I haven't seen the opposite: dark, fresh craters on the light-toned regions. This leads me to suspect that the black is a thin dusting over the white, whereas the white is a thicker layer. I think this is absolutely correct. But the truth may be a little more complex. Most icy moons have a surface somewhat darker than ice. Impacts tend to surface whiter ice underneath. But the surface isn't dark, just "dingy". I suppose that Iapetus's native regolith was like that -- similar to what we see on Rhea. The places where dark has spread, the top surface layer has lost its ice, leaving only the dark stuff behind. This could be, and is almost bound to be, quite thin. If the ice that sublimated away from dark stuff has settled onto the original dingy surface in non-black areas, then we have at least three layers: fresh ice deep in the crust, a dingy regolith, and a fresh white coating of frost. So an impact in the white areas would surface a tiny bit of dingy material, but far more white ice. |
|
|
Lo-Fi Version | Time is now: 28th March 2024 - 05:02 PM |
RULES AND GUIDELINES Please read the Forum Rules and Guidelines before posting. IMAGE 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 funded by the Planetary Society. Please consider supporting our work and many other projects by donating to the Society or becoming a member. |