IPB

Welcome Guest ( Log In | Register )

4 Pages V  < 1 2 3 4 >  
Reply to this topicStart new topic
The Bright Spots on Ceres
David Palmer
post Mar 31 2015, 08:50 PM
Post #16


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



QUOTE (dudley @ Mar 31 2015, 11:29 AM) *
I'm not really clear on why the proposed 'spring mound' would need to be tall and thin in shape. If it's 4 km across, and the crater is a couple of km deep, the mound could be three km tall, and still catch the Sun when the crater was dark, couldn't it? The strong brightening reported for the bright spot at about local noon seems to point to a fairly broad, flat feature. A tall, thin feature would present nearly minimum aspect to the Sun at this time, would it not?



I was suggesting that it was tall compared to its base, RELATIVE to what we would see on the higher-gravity Earth or even Mars. Mt. Sharp in Gale Crater of Mars is considered a "high," relatively steep mountain with its summit 5.5 km above its base, but the base is about 80 km wide.....which are proportions similar to what we see with "stratovolcanoes" on Earth (totally different geologic origin from Mt. Sharp, of course)....the upshot being that we're used to mountains being much wider than they are high, so to see one that would be of about the same height as the width (similar to Wyoming's Devils Tower, made famous in "Close Encounters"), would strike us as being very dramatic indeed, and visually would appear quite "spindly." Whereas an Earthly "spring mound" would always be a low-relief feature due to the far higher gravity.

To be one pixel (or smaller) in diameter as seen from the photographed distance, while simultaneously projecting above the crater rim, we're probably looking at a feature no wider than it is tall. A change in brightness with the changing sun angle in conjunction with the changing angle of view from the spacecraft, may be related to the reflective properties and orientation of the ice crystals and/or salt crystals making up its surface (although we could also be dealing with mirror-like relfections off glass surfaces, if we want to consider the artificial-construct model.....but of course, that would be a hypothesis of last resort, and as Sagan said, "extraordinary claims require extraordinary evidence").
Go to the top of the page
 
+Quote Post
Gladstoner
post Mar 31 2015, 10:21 PM
Post #17


Member
***

Group: Members
Posts: 646
Joined: 3-January 08
Member No.: 3995



As we've heard, something noteworthy was spotted when the bright-spot area was near the limb (or at least that's been the impression). It's interesting that no images of this have yet been released -- including the missing frames in the gibbous-Ceres rotation sequence. Other unreleased images of the bright spot(s) at the limb likely include the half- and crescent-Ceres images, as well as any unscheduled imagery (which very well could have been taken if something extraordinary was spotted).

Plus, if there are geysers/spring mounds present, they could consist of a field of structures rather than a single edifice:

Attached Image


On Earth, fields of small cinder cones form when magma ascent becomes insufficient to form a single volcano. Compare Mauna Loa with the volcanic field around Flagstaff, Arizona. Any activity on Ceres could be meager, so I'd think a field of vents would be more likely.

Plus, visible plumes may not necessarily be the same thing as the bright spots as we've seen them. As the area moves close to the limb while Ceres is in a crescent phase, any otherwise faint plumes could become visible when back lit, even if the bright terrain becomes less conspicuous:

Attached Image


Again, all of this considers the possibility of venting activity. The truth could hold something completely different in store.
Go to the top of the page
 
+Quote Post
ollopa
post Mar 31 2015, 11:05 PM
Post #18


Junior Member
**

Group: Members
Posts: 85
Joined: 25-November 04
From: Dublin, Ireland
Member No.: 113



I'd hate this thread to get embarrassingly out of hand. I met one MPI person at LPSC who just shrugged: "Pixels". (a short) Time will tell.
Go to the top of the page
 
+Quote Post
Gladstoner
post Mar 31 2015, 11:30 PM
Post #19


Member
***

Group: Members
Posts: 646
Joined: 3-January 08
Member No.: 3995



Well, the "pixels" in question seem to be in still-unreleased images as indicated here:

http://www.nature.com/news/bright-spots-on...=TWT_NatureNews

Quote:

New images from NASA’s Dawn spacecraft show the spots, known as ‘feature number 5’, at changing angles as the dwarf planet rotates in and out of sunlight. The pictures reveal the spots even when they appear near the edge of Ceres, when the sides of the impact crater would normally block the view of anything confined to the bottom. That something is visible at all in this circumstance suggests that the feature must rise relatively high above the surface.

“What is amazing is that you can see the feature while the rim is still in the line of sight,” said Andreas Nathues, a planetary scientist at the Max Planck Institute for Solar System Research in Göttingen, Germany. Nathues, who leads the team for one of the Dawn cameras, revealed the images on 17 March at the Lunar and Planetary Science Conference in The Woodlands, Texas.


In the meantime, we have to rely on the quote above, released images, and our imagination. smile.gif
Go to the top of the page
 
+Quote Post
David Palmer
post Apr 1 2015, 05:14 AM
Post #20


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Gladstoner: I doubt that an extended field of vents is consistent with the one-pixel (or less) size of the bright spot. Plus, such small vents would not account for the apparent protrusion of the top of the mysterious object above the crater rim. And as I explained in my original posting, a plume is not plausible, as it would have coated the surrounding landscape with snow (like what we see on Enceladus).

MOD: All-caps comment removed for violation of rule 2.6.
Go to the top of the page
 
+Quote Post
Explorer1
post Apr 1 2015, 05:47 AM
Post #21


Senior Member
****

Group: Members
Posts: 1424
Joined: 13-February 10
From: British Columbia
Member No.: 5221



Because they are under no obligation to do so yet.
Maybe after Opnav 6 finds out the ground truth they'll be shown? Otherwise it would just be more speculation....
Go to the top of the page
 
+Quote Post
Gladstoner
post Apr 1 2015, 08:31 AM
Post #22


Member
***

Group: Members
Posts: 646
Joined: 3-January 08
Member No.: 3995



QUOTE (David Palmer @ Apr 1 2015, 12:14 AM) *
I doubt that an extended field of vents is consistent with the one-pixel (or less) size of the bright spot. Plus, such small vents would not account for the apparent protrusion of the top of the mysterious object above the crater rim..... a plume is not plausible, as it would have coated the surrounding landscape with snow (like what we see on Enceladus).


Ice coatings on Enceladus are deposited as the moon sweeps up material from the E ring, which was originally derived from the moon's plumes (or at least that's how I've understood it).

In Ceres' case, escaped plume material would be more likely to spread out completely along its much larger solar orbit. Plus, the ice particles would be more susceptible to sublimation being so much closer to the sun.

And at 4 km/pixel, there is still potentially quite a bit of real estate covered. smile.gif

Again, this may all be for nothing when we learn the truth in the next weeks and months, but it's fun to play with the cards dealt on the table.
Go to the top of the page
 
+Quote Post
David Palmer
post Apr 1 2015, 11:58 AM
Post #23


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



QUOTE (Explorer1 @ Mar 31 2015, 10:47 PM) *
Because they are under no obligation to do so yet.
Maybe after Opnav 6 finds out the ground truth they'll be shown? Otherwise it would just be more speculation....


If it were a private enterprise, that could be the case, but because it is taxpayer funded, it seems to me that they have an obligation to immediately release everything (and if they don't, it just fuels conspiracy-type theories, to the effect that they're trying to hide something).
With the Mars rover Curiosity, all raw photos are quickly released on a dedicated website, and I don't know why things should be any different with Dawn.
Go to the top of the page
 
+Quote Post
David Palmer
post Apr 1 2015, 12:20 PM
Post #24


Junior Member
**

Group: Members
Posts: 33
Joined: 16-June 14
From: Sweet Home, Oregon
Member No.: 7202



Reply to Gladstoner: you make a good point, that ice is a lot less stable at Ceres as compared with Enceladus, and so it would be harder to coat the surface, and for any such coating to persist. However, that point could also be used as an argument against the hypothesis of a currently-active plume: if there were a plume that was intense enough to generate the bright spot, and the component ice crystals evaporated before the plume was able to spread out and coat the surface, then the water vapor emission signal from Ceres should be FAR stronger than what was picked up by Herschel, and it should also be continuous (not just the wisp of vapor detected at perihelion that we would expect from 0.6 square km of exposed ice).
I'm thinking that a sharp mountain-shaped spring mound would fit the observations best, but that the surface is likely to be rather dessicated and consist mostly of a crust of salt over a core of ice, where the salt is an evaporative remnant that would serve to protect the ice from further rapid evaporation (and bring the water vapor signal in line with the minimal amount detected by Herschel), but such a crust would also be nearly as reflective as snow.
Go to the top of the page
 
+Quote Post
algorimancer
post Apr 1 2015, 01:42 PM
Post #25


Member
***

Group: Members
Posts: 655
Joined: 20-April 05
From: League City, Texas
Member No.: 285



QUOTE (David Palmer @ Apr 1 2015, 05:58 AM) *
...because it is taxpayer funded, it seems to me that they have an obligation to immediately release everything...

Unfortunately for us, that happens not to be the case. Certainly not "immediately"... they have a schedule when imagery will be moved into a public archive, and it is months as opposed to minutes.

For a broader perspective, I work (as a statistician) in medical research. Public release of raw data almost never happens in this field, only partially because of patient confidentiality issues. Even raw lab data is rarely released. The product is publications of summaries & interpretations of the data. Sadly, this is associated with a bias where results which displease someone tend not to be published, whether because the results conflict with what has been previously published (potentially embarrassing) or because no statistical or practical significance was found (difficult to find journals interested in publishing). From this perspective, I'm absolutely amazed and pleased with the imagery releases by the planetary science community -- which is not to say that I would not enjoy greater openness even more.
Go to the top of the page
 
+Quote Post
dudley
post Apr 1 2015, 03:33 PM
Post #26


Junior Member
**

Group: Members
Posts: 41
Joined: 27-March 15
Member No.: 7426



It's been reported that thermal measurements of the bright spots reveal that they have the same temperature as their surroundings. This was considered surprising since light-colored areas should reflect more light, and, so, remain cooler than dark ones.
If there is continual freezing of water emerging from the interior, this would release a certain amount of heat. It seems a remarkable coincidence that this added heat would affect the bright spots' heat budget to just the right degree, so as to make it very closely match that of their darker surroundings.
Go to the top of the page
 
+Quote Post
Explorer1
post Apr 1 2015, 04:05 PM
Post #27


Senior Member
****

Group: Members
Posts: 1424
Joined: 13-February 10
From: British Columbia
Member No.: 5221



http://www.planetary.org/blogs/guest-blogs...raph-ceres.html

According to this, there is still some uncertainty in the rotation rate, so some uncertainty about whether the spots will show up on the (still thin) crescent). Consequence of the fast rotation.
Go to the top of the page
 
+Quote Post
katodomo
post Apr 1 2015, 04:11 PM
Post #28


Junior Member
**

Group: Members
Posts: 77
Joined: 20-September 14
Member No.: 7261



QUOTE (David Palmer @ Apr 1 2015, 12:58 PM) *
If it were a private enterprise, that could be the case, but because it is taxpayer funded, it seems to me that they have an obligation to immediately release everything

Just as a clarification, Dawn's framing camera was effectively paid 50% from R&D funds of the German Ministry of Science and 50% from (non-taxpayer-related) own funds of the Max Planck Society. MPAe in fact had to push quite a bit through the local federal parliament reps to get the government's contribution. JPL contributed a small sum, basically buying rights to use the camera for navigation that way.

Go to the top of the page
 
+Quote Post
fredk
post Apr 1 2015, 05:07 PM
Post #29


Senior Member
****

Group: Members
Posts: 3766
Joined: 17-January 05
Member No.: 152



QUOTE (David Palmer @ Apr 1 2015, 12:58 PM) *
With the Mars rover Curiosity, all raw photos are quickly released on a dedicated website, and I don't know why things should be any different with Dawn.

MER, Cassini, and MSL are the exceptions, not the rule. You can read more about the reasons for this on this forum and elsewhere, but essentially we have scientists spending years (and sometimes decades) of their lives working on a mission and they deserve to be able to publish any discoveries made with the mission themselves. In some cases releasing images or data publicly might allow scientists not on the mission to publish the discoveries first.

With the three exceptions, it was deemed unlikely that many important discoveries would be made with the images themselves, so it was safe to release them in real time. When you're visiting a body for the first time, like Ceres or Comet 67P C-G, it's possible or even likely that the images will reveal important new discoveries, so their release is limited.
Go to the top of the page
 
+Quote Post
nprev
post Apr 2 2015, 04:13 AM
Post #30


Senior Member
****

Group: Admin
Posts: 7955
Joined: 8-December 05
From: Los Angeles
Member No.: 602



MOD MODE: Thanks to the members who have correctly pointed out that image release policies can and will vary between missions,

I also must remind all to keep rules 1.9 and 2.6 firmly in mind at all times. Spurious accusations and/or conspiracist conjectures or implications will be removed immediately and members posting same may be suspended. This is the first and last warning.


--------------------
A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.
Go to the top of the page
 
+Quote Post

4 Pages V  < 1 2 3 4 >
Reply to this topicStart new topic

 



RSS Lo-Fi Version Time is now: 21st July 2017 - 06:51 PM
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.