APOD: Dark Craters and Bright Spots on... (2015 Feb 18)

[geckzilla]

It seems that we've taken too much away from that conclusion, though. At Hubble's resolution, the spot could have been a diffuse area of slightly different albedo or, as we've come to discover, a small area of apparently significantly different albedo.

Yes, but we were right to stick with that conclusion, rather than speculate over a handful of new, higher resolution images from Dawn, with hardly any published technical details. Once technical details of the newest images become available publicly, the situation will be different.

But it is also wrong to stick so steadfastly to a certain number without openly accepting the various possibilities of what range of conditions could reasonably exist given that particular measurement.

[Nitpicker]

Not sure that anyone was being quite so steadfast on the 9% being the ultimate answer. However, I am quite sure that "barely a 9% higher albedo than the surrounding surface" was the best answer based on the Hubble dataset, where the pixels were more than 30 km across. The Dawn images from Feb 19, have pixels more than 4 km across (~50 times more pixels per area). But in the absence of technical/processing details for the Dawn images, one cannot begin to revise the map of variable albedo with any validity.

It would not be a great surprise to find ice of some form and in some proportion, weathered to some degree, on the surface of Ceres. It is entirely expected. But not because of "Mass Vortex theory" and not contrary to the analysis of the Hubble dataset (which Sally has drastically misinterpreted in her posts so far).

It should also be noted that there are quite a few different kinds of albedo measurements and they are all frequently mixed up and bandied about by amateur enthusiasts, making the numbers somewhat rubbery. Not to mention that variable albedo measurements are all dependent on resolution in one way or another. I am sure the figures I've quoted for variation of albedo on the Moon, are not based on the best photographic resolution currently possible. I'd bet there are small patches/pebbles/grains on the surface of the Moon, that reflect light with a much higher albedo than the quoted maximum of 0.183.

Edit reason: revised numbers in first paragraph.

[geckzilla]

Alright, but the message I took away from earlier in the thread was a very rigid and one dismissive of nearly any possibility, be it outlandish or reasonable.

[Nitpicker]

Certainly dismissive of the rationale of some.

[geckzilla]

It would have been nice to have had some guidance into a more appropriate direction instead of complete dismissal, that's all. Hindsight is 20/20

[Nitpicker]

It would have been nice to have had some guidance into a more appropriate direction instead of complete dismissal, that's all. Hindsight is 20/20

Huh?

[geckzilla]

You seem to be taking it personally. I'm saying we should have talked about what Hubble's albedo measurements meant. I'm annoyed that I didn't interpret it very well, myself.

[Nitpicker]

Well, yes, it appears I have largely misinterpreted you today.

Here is a brief conference paper discussing the Hubble results. Note "Fig. 2." showing maximum albedo 8% higher than global average:
http://www.lpi.usra.edu/meetings/abscic ... f/5455.pdf

[geckzilla]

Yes, the results in that paper are no doubt accurate for an average albedo measurement over the surface of Ceres. But it says little or nothing about the characteristics of small, isolated features such as the bright patch. To state that the patch can't be bright because of these measurements is erroneous. Now that we have a closer look at just how small it is, it is remarkable that it shows up at all in Hubble's images. I'm leaning towards the conclusion that the patch is very bright indeed.

[Nitpicker]

Yes, the results in that paper are no doubt accurate for an average albedo measurement over the surface of Ceres. But it says little or nothing about the characteristics of small, isolated features such as the bright patch. To state that the patch can't be bright because of these measurements is erroneous. Now that we have a closer look at just how small it is, it is remarkable that it shows up at all in Hubble's images. I'm leaning towards the conclusion that the patch is very bright indeed.

But given that we know the Hubble pixels have an area of about 900 km², if the albedo of the bright patches is 1.0, they must have an area of about 10 km². If the albedo of the patches is 0.4, they must have an area of about 30 km². (In nice round figures.)

[geckzilla]

Now you're talking.

[Nitpicker]

I'm saying we should have talked about what Hubble's albedo measurements meant. I'm annoyed that I didn't interpret it very well, myself.

I don't think anyone realised, initially, that the "mystery" link from the APOD caption, was quoting the Hubble results -- "barely a 9% higher albedo than the surrounding surface" -- whilst discussing the Dawn images. Having said that, the "mystery" link is dated only a week or so after Dawn's image resolution began to exceed Hubble's, and only a day or so after Dawn doubled that resolution. The "mystery" link also stated: "The resolution of the photographs are currently at 14 kilometers (8.5 miles) per pixel, so we don't yet have enough detail to resolve if these are pinprick spots, or brighter regions that are blurring into points through our fuzzy vision."

[sallyseaver]

Thank you, Geckzilla , for representing my concern regarding a steadfast sticking to the 9% number at a time when the reports are that scientists are surprised by the light spots and light areas on Ceres. And thank you so much for passing on the information from Chris Russell regarding a possible 0.4 albedo for the bright white spot on Ceres. I receive your caution that it is a casual report, not a formally published - and there fore reliable - report.

Nitpicker, thank you for explaining why you had the confidence about the 9% number. I am properly chastened for trying to report results from a dataset that I did not understand as I should have. I hope that someday I can convince you that my lack of understanding about albedo measurements and datasets does not translate to a lack of understanding about mass, space, time, physics and planet formation.

I think this comment of yours is particularly relevant to our conversation:

It should also be noted that there are quite a few different kinds of albedo measurements and they are all frequently mixed up and bandied about by amateur enthusiasts, making the numbers somewhat rubbery. Not to mention that variable albedo measurements are all dependent on resolution in one way or another. I am sure the figures I've quoted for variation of albedo on the Moon, are not based on the best photographic resolution currently possible. I'd bet there are small patches/pebbles/grains on the surface of the Moon, that reflect light with a much higher albedo than the quoted maximum of 0.183.

This comment, on the other hand, seems a little out of place:

Yes, but we were right to stick with that conclusion, rather than speculate over a handful of new, higher resolution images from Dawn, with hardly any published technical details. Once technical details of the newest images become available publicly, the situation will be different.

C'mon, Nitpicker, you wouldn't publish a paper on results from a new constrast-enhanced image, but isn't the purpose of this thread to conjecture on the new, higher-resolution images from Dawn, given the new unexpected results? (And if there was not an interest in finding a new explanation for unexpected results, I would not have jumped in with my explanation from Mass Vortex Theory.)

Given your commitment to Standard Theory (the current status quo consensus), please explain why you say the following:

It would not be a great surprise to find ice of some form and in some proportion, weathered to some degree, on the surface of Ceres. It is entirely expected.

I thought that planets and asteroids were supposedly formed from rocky material in orbit around the newly formed sun colliding, generating heat, separating into layers, and then gradually cooling down. An ice layer has never been part of the Standard-Theory explanation for planet, or dwarf-planet formation that I have seen (I freely admit that I am not as acquainted with the literature as you are). We have some observations about ice layers on some moons, but I have not seen a Standard-Theory explanation for this observed feature.

With Ceres, you have the problem of an ice layer plus another layer of rocky debris on top. You say that the ice could be "weathered to some degree," but space weather does not account for rocky material distributed over the whole surface. As far as I know, space weather has to do with high speed ions and electrons discharged by the sun; space weather is monitored by ground-based magnetometers and magnetic observatories. So, space weather involves electromagnetic forces and charged particles, not rocky stuff.

Please explain why an ice layer with a dusting of rocky material fits within the explanation of Standard Theory. [I think other readers may be interested in this also.]

[geckzilla]

I don't know if I'm defending (or attacking for that matter) anyone's ideas so much as I am beating myself up for being a know-it-all earlier even though I didn't post my thoughts on the matter to reveal as much. And Nitpicker points out that the facts were all right there in writing but it's something I still failed to understand. I still won't say it's any kind of ice right now but especially water ice would be a very strange and unusual thing indeed. I just think it's much brighter than originally suspected.

[Nitpicker]

I don't understand why small localised ice patches would be so unexpected on Ceres (especially if they are supplied from the mantle via some mechanism). Its semi-major axis lies just beyond the water frost line of the Solar system (which just happens to divide the main asteroid belt). Ceres has a density only twice that of water, indicating that it is likely to contain a lot of it. It has a noticeable oblateness, which could indicate a rocky core and an icy mantle. And its spectra tell of a crust rich in hydrated minerals, indicating water below.

And Sally, as for my confidence in the 9% number, I think it was more a case of my lack of confidence in your method of disputing it (which was totally bogus). And as for the formation of the Solar System, I'm not so familiar with the literature, but I am less familiar with the notions that you appear to attribute to the "standard model". You will need to argue your case in much smaller steps if you want me to take your theories seriously. There is a helluva lot of H₂O in the Solar System and resonances with migrating gas giants, would appear to be the most likely cause of its wide distribution.

[geckzilla]

It is not the mere presence of ice that is unexpected to me but its existence in an isolated but apparently fresh state on the surface of a world not obviously undergoing any other sort of activity. Look at those craters. It looks pretty old.

[Nitpicker]

It is not the mere presence of ice that is unexpected to me but its existence in an isolated but apparently fresh state on the surface of a world not obviously undergoing any other sort of activity. Look at those craters. It looks pretty old.

But it possibly matches with this:
http://www.esa.int/Our_Activities/Space ... anet_Ceres

[geckzilla]

Maybe so. I'm definitely dubious of the whole cryovolcano thing. Or perhaps it's the volcano part which bothers me because when I think of volcanoes I think of a very active surface that sees a lot of remodeling. Ceres holds its secrets for another day.

[Nitpicker]

Maybe so. I'm definitely dubious of the whole cryovolcano thing. Or perhaps it's the volcano part which bothers me because when I think of volcanoes I think of a very active surface that sees a lot of remodeling. Ceres holds its secrets for another day.

“We estimate that approximately 6 kg of water vapour is being produced per second, requiring only a tiny fraction of Ceres to be covered by water ice, which links nicely to the two localised surface features we have observed,” says Laurence O’Rourke, Principal Investigator for the Herschel asteroid and comet observation programme

It doesn't sound quite violent enough to be like any kind of volcano I've ever heard of. My toilet flush probably has a flow rate of 6 litres per second!

But the notion of a cross-over in the classification of asteroids and comets (and also, independently, of terrestrial planets forming with a significant supply of water-bearing, hydrated minerals) is quite compelling to me.

Dawn is going to take quite a while to spiral in really close to Ceres. I understand it won't achieve its maximum planned image resolution (<100 m per pixel) until the end of the year. And it might be a few months yet before these bright spots are close enough to be resolved convincingly.

[geckzilla]

It doesn't sound quite violent enough to be like any kind of volcano I've ever heard of. My toilet flush probably has a flow rate of 6 litres per second!

Yes, exactly. Either I need to accept this new form of "volcano" as an adequate word for describing such a phenomenon which may also bear analogous similarities to typical volcanoes or a different word would be more appropriate. Why not geyser? It seems to work for Enceladus. Cryovolcano is catchy, I suppose, but if you could safely walk around in it and not even notice the water movement, it's totally overrated.

[Nitpicker]

It doesn't sound quite violent enough to be like any kind of volcano I've ever heard of. My toilet flush probably has a flow rate of 6 litres per second!

Yes, exactly. Either I need to accept this new form of "volcano" as an adequate word for describing such a phenomenon which may also bear analogous similarities to typical volcanoes or a different word would be more appropriate. Why not geyser? It seems to work for Enceladus. Cryovolcano is catchy, I suppose, but if you could safely walk around in it and not even notice the water movement, it's totally overrated.

Comet-like sublimation seems more likely at this stage. But "geysers" seem to be used fairly regularly to describe cryo-volcanic eruptions.

[neufer]

“We estimate that approximately 6 kg of water vapour is being produced per second, requiring only a tiny fraction of Ceres to be covered by water ice, which links nicely to the two localised surface features we have observed,” says Laurence O’Rourke, Principal Investigator for the Herschel asteroid and comet observation programme

It doesn't sound quite violent enough to be like any kind of volcano I've ever heard of.
My toilet flush probably has a flow rate of 6 litres per second!

The TITY-BOLE LAW: Many Volcanoes Erupt Marshmallows, Certainly!

[Chris Peterson]

It is not the mere presence of ice that is unexpected to me but its existence in an isolated but apparently fresh state on the surface of a world not obviously undergoing any other sort of activity. Look at those craters. It looks pretty old.

I don't think there's anything surprising or unexpected at all. Asteroids have low albedos because they have space weathered surfaces. Ceres may have an underlying surface layer with a high ice content, but even if it doesn't, any unweathered rock will be higher albedo. So a meteorite impact will almost certainly create a spot that is more reflective.

Large impacts are rare; small ones are not. It is probably harder to explain a large area that is just a few percent brighter than it is a small spot that is a few hundred percent brighter.

In any case, I don't think the mission scientists are surprised by the spot (or spots) at all. It would be very strange indeed if Ceres didn't have a varied surface (like every other body in the Solar System). Everyone is curious about the nature of the variation, not surprised it is present.

[Ron-Astro Pharmacist]

The TITY-BOLE LAW: Many Volcanoes Erupt Marshmallows, Certainly!

Welcome back "Billy". Hope you enjoyed your vacation!! Hope all's well with Montana. Oh – I forget this is a Ceres discussion. Anyone know how hot it gets in the center of an asteroid of that size?

[Ann]

Hi, Art, welcome back!

Ann