IPB

Welcome Guest ( Log In | Register )

31 Pages V  « < 21 22 23 24 25 > »   
Reply to this topicStart new topic
Dawn's first orbit, including RC3, March 6, 2015- June 15, 2015
Gladstoner
post May 29 2015, 05:36 PM
Post #331


Member
***

Group: Members
Posts: 685
Joined: 3-January 08
Member No.: 3995



QUOTE (Habukaz @ May 29 2015, 11:26 AM) *
Also, what is that (apparently) huge thing to the lower right? Is it a double crater, or is it just an awkward angle? It looks kind of bilobate.


It's an impact basin, but so far, it's been tricky to interpret. There appears to be topographic (tectonic?) variations on the floor similar to those in the equatorial 'sand dollar' basin, along with terrain modification ('valleying' and whatever else) of the rim. Oh, and albedo variations. No wonder the initial approach images were so confusing.
Go to the top of the page
 
+Quote Post
belleraphon1
post May 30 2015, 12:01 AM
Post #332


Member
***

Group: Members
Posts: 813
Joined: 29-December 05
From: NE Oh, USA
Member No.: 627



Cannot take my eyes off latest DAWN image release and fredk's stretch. Here we have a body with a density of 2 and one that has never gone through the tidal processing that some of the outer planet moons with similar densities have experienced.

THIS IS SO COOL. If Ceres did not exist, theorists would have had to invent it as a starting point.

Big thank you to DAWN team for these image releases. And I have to second jgoldader praise several posts back on the incredible expertise of the personnel on unmannedspaceflight. Blow my mind every day.

Okay, back to lurking.

Craig
Go to the top of the page
 
+Quote Post
Gladstoner
post May 30 2015, 03:36 AM
Post #333


Member
***

Group: Members
Posts: 685
Joined: 3-January 08
Member No.: 3995



Today's release vs. January:

Attached Image
Go to the top of the page
 
+Quote Post
ElkGroveDan
post May 30 2015, 04:20 PM
Post #334


Senior Member
****

Group: Admin
Posts: 4750
Joined: 15-March 05
From: Sloughhouse, CA
Member No.: 197



QUOTE (fredk @ May 29 2015, 08:18 AM) *
A stretch of the latest image shows well the albedo variations:
[attachment=35934:PIA19562_stretch.jpg]

I have to say that this is the "WOW" image for Ceres that I've been waiting for.


--------------------
If Occam had heard my theory, things would be very different now.
Go to the top of the page
 
+Quote Post
ngunn
post May 30 2015, 08:42 PM
Post #335


Senior Member
****

Group: Members
Posts: 3461
Joined: 4-November 05
From: North Wales
Member No.: 542



I can undertand recently exposed ice on Ceres being active in the sense that as it sublimes it may carry other materials upward in a comet-like fashion. I have one worrry and one question. The worry first: The primary reason for the exposure of the ice may not be evident even at high resolution. Whether venting due to some internal process or impact cratering is responsible there may have been subsequent processes such as scarp retreat that erase the tell-tale clues.

The question: Why would a plume of material from Ceres deposit dirt preferentially in one direction?
Go to the top of the page
 
+Quote Post
alk3997
post May 30 2015, 09:06 PM
Post #336


Member
***

Group: Members
Posts: 112
Joined: 31-January 15
From: Houston, TX USA
Member No.: 7390



QUOTE (ngunn @ May 30 2015, 02:42 PM) *
...

The question: Why would a plume of material from Ceres deposit dirt preferentially in one diraction?


Direction of Ceres rotation would be one reason. The floating material which would then fall at different location depending upon the length of time each piece was aloft as Ceres rotated beneath it.

Andy
Go to the top of the page
 
+Quote Post
alk3997
post May 30 2015, 09:10 PM
Post #337


Member
***

Group: Members
Posts: 112
Joined: 31-January 15
From: Houston, TX USA
Member No.: 7390



As we've been pondering bright spots, I've wondered about this dark crater (circled) just south of bright area #5.

Attached Image


To me it looks like the dark material has filled-in this crater leaving just a central peak. I've been looking for other images of that location that are higher resolution but nothing yet.

Andy
Go to the top of the page
 
+Quote Post
Hungry4info
post May 30 2015, 09:25 PM
Post #338


Senior Member
****

Group: Members
Posts: 1168
Joined: 26-July 08
Member No.: 4270



It's simply grote in the camera. You see it in different places on Ceres in different images.


--------------------
-- Hungry4info (Sirius_Alpha)
Go to the top of the page
 
+Quote Post
Gladstoner
post May 31 2015, 12:34 AM
Post #339


Member
***

Group: Members
Posts: 685
Joined: 3-January 08
Member No.: 3995



QUOTE (ngunn @ May 30 2015, 03:42 PM) *
The question: Why would a plume of material from Ceres deposit dirt preferentially in one direction?


Also, the vent (or vents) could be oriented in a certain direction. In the airless environment, the ejecta would follow a ballistic trajectory.
Go to the top of the page
 
+Quote Post
ZLD
post May 31 2015, 03:00 AM
Post #340


Member
***

Group: Members
Posts: 551
Joined: 27-September 10
Member No.: 5458



QUOTE (Gladstoner @ May 30 2015, 06:34 PM) *
Also, the vent (or vents) could be oriented in a certain direction. In the airless environment, the ejecta would follow a ballistic trajectory.


This would make the most sense to me as well, especially if such a vent was present in a fault zone.


--------------------
Go to the top of the page
 
+Quote Post
Gerald
post May 31 2015, 01:18 PM
Post #341


Senior Member
****

Group: Members
Posts: 2238
Joined: 7-December 12
Member No.: 6780



Yet another stretch of pia19562.tif, cropped and magnified twice:
Attached Image

It shows, besides some texturing due to temporary jpg compression, brightness variations with some analogy to "the" bright spot, but with the advantage, that it's on a larger scale, hence better resolved.
Particularly along the south-western rim of the basin there seem to be parallel structures, which resemble pretty much terraces of some exposed strata.
Go to the top of the page
 
+Quote Post
DFortes
post May 31 2015, 01:21 PM
Post #342


Junior Member
**

Group: Members
Posts: 41
Joined: 11-April 07
From: London, U.K.
Member No.: 1957



QUOTE (alk3997 @ May 30 2015, 10:06 PM) *
Direction of Ceres rotation would be one reason. The floating material which would then fall at different location depending upon the length of time each piece was aloft as Ceres rotated beneath it.

Andy


No. The plume particles would share the same angular velocity as Ceres. If you jump in the air, the Earth doesn't rotate beneath you!
Go to the top of the page
 
+Quote Post
scalbers
post May 31 2015, 02:35 PM
Post #343


Senior Member
****

Group: Members
Posts: 1339
Joined: 5-March 05
From: Boulder, CO
Member No.: 184



QUOTE (Gladstoner @ May 29 2015, 05:36 PM) *
It's an impact basin, but so far, it's been tricky to interpret. There appears to be topographic (tectonic?) variations on the floor similar to those in the equatorial 'sand dollar' basin, along with terrain modification ('valleying' and whatever else) of the rim.

Here's a (somewhat reduced resolution) excerpt from an updated map I'm working on that shows this basin on the right side. It's mainly a mix of two images with a crescent view in the south and the favorite new low phase angle view (PIA19562) on the north.

Attached Image


The wandering depression (or set of crater chains and/or extra small crater rims?) off to the NNE side of the basin has a somewhat sinuous appearance. Here is another way to compare images - click below for a blinking animation.

Attached Image


--------------------
Go to the top of the page
 
+Quote Post
fredk
post May 31 2015, 02:35 PM
Post #344


Senior Member
****

Group: Members
Posts: 3898
Joined: 17-January 05
Member No.: 152



QUOTE (DFortes @ May 31 2015, 02:21 PM) *
No. The plume particles would share the same angular velocity as Ceres. If you jump in the air, the Earth doesn't rotate beneath you!

That's correct, for a very local eruption. As the plume gets larger, the Coriolis force will become important. The Coriolis force will cause a radial plume to pick up some rotation relative to Ceres, at least at higher latitudes. Especially near the equator, there will also be a vertical component to the Coriolis force (for approximately horizontal-directed plume components), which will be opposite for eastward and westward directed plume components. Also the vertical-directed part of the plume will be deflected westward. So it's conceivable that this could cause an east-west asymmetry.

My guess is that the dark deposit (if that's what it is) east of region 5 is much too close to the source for the Coriolis effects to produce such a large asymmetry.
Go to the top of the page
 
+Quote Post
DFortes
post May 31 2015, 05:09 PM
Post #345


Junior Member
**

Group: Members
Posts: 41
Joined: 11-April 07
From: London, U.K.
Member No.: 1957



QUOTE (fredk @ May 31 2015, 03:35 PM) *
That's correct, for a very local eruption. As the plume gets larger, the Coriolis force will become important. The Coriolis force will cause a radial plume to pick up some rotation relative to Ceres, at least at higher latitudes. Especially near the equator, there will also be a vertical component to the Coriolis force (for approximately horizontal-directed plume components), which will be opposite for eastward and westward directed plume components. Also the vertical-directed part of the plume will be deflected westward. So it's conceivable that this could cause an east-west asymmetry.

My guess is that the dark deposit (if that's what it is) east of region 5 is much too close to the source for the Coriolis effects to produce such a large asymmetry.


Sigh. The reason I didn't mention Coriolis forces is because they're likely to be negligible (as you agree). A simple calculation of the Rossby number shows that inertial forces in any supposed plume (which, I might add, I don't think is an explanation for anything on Ceres) will dominate over Coriolis forces.

The Coriolis parameter, f = 2(ω).sin(φ), where ω = 1.9234x10-4 rad s-1 and φ is the latitude.

For a plume at mid-latitudes (φ = 45) involving particles erupted at, say, 250 m s-1 over a length scale that appears from the images to be around 100 km, then the Rossby number is ~ 10
For Coriolis forces to become marginally important on these length scales, the eruption velocities would need to be nearer 30 m -1 (about 70 mph).

It's worth adding that ballistic emplacement over a maximum distance of 100 km in a gravity field of 0.27 m s-2 requires a muzzle velocity of about 165 m s-1 (and yes, I'm assuming planetary curvature is insignificant).
Go to the top of the page
 
+Quote Post

31 Pages V  « < 21 22 23 24 25 > » 
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 22nd February 2019 - 10:50 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.