Dawn at Ceres Thread

[baggers]

It's a shame the payload of 15 science instruments initially intended to Dawn was reduced to 3: the camera, the infrared camera, the gamma/neutron spectrometer.

But back in 2006, it's 3 instruments or no Dawn at all, so...

[Newt]

How in the world could it be ice? Who knows. Maybe it really is salt or some kind of white clay or sand or something

This is an opinion (the salt) that I have heard in some conversations with astrogeologists. That was a few weeks ago, but their idea was basically something erupts out of the surface, and, as the water/ice sublimate and escape, salt and other minerals could fall back to the surface. This would have happened exremely recently.

WHEN are we actually going to be able to know for sure what it is? CAN Dawn distinguish between salt and ice? Will we just get better and better pictures of it and but never be able to tell what it is? Don't they have some kind of neutron spectroscopy crap or something?

Dawn has spectrometers, that will be able to differentiate the two. Resolution, is, at the moment, too low, pending getting closer. Additionally, calibration is somewhat slow from my understanding, and they need to get that right before they can make any accurate measurments. Previous infared images did not show the spots at all (which to one geologist suggested it was not ice), but, again, resolution makes such conclusions difficult at this time.

I suppose if its sublimating into space, you might be able to detect water vapor/oxygen/hydroxyl/hydrogen when you flew over the spots,

There was a visible eruption on Ceres some time ago, exactly at the exciting white spots.

Could it be a comet or asteroid that broke apart shortly before impact? Like Shoemaker-Levy 9 and Jupiter?

That occured as a result of Jupiter's fantastic mass and gravity. I am skeptical that Ceres could have the same effect, being so much smaller. Perhaps with the right comet? That seems strange. What about the water plume we saw comming from the same spot? Though that could be from a comet impact, it seems like the composition would have been different.

[Streetwind]

For all Polandball fans... (...and those who will enjoy the subtle KSP reference...)

Ceres is of friendly!

[winged]

For all Polandball fans... (...and those who will enjoy the subtle KSP reference...)

Ceres is of friendly!

cool!

BTW. Are there any colour pictures of Ceres? I mean pictures with natural colors (assumptions of what naked eye would have seen) not exxagerated to show some features.

[lajoswinkler]

"Dawn scientists can now conclude that the intense brightness of these spots is due to the reflection of sunlight by highly reflective material on the surface, possibly ice,"- http://www.nasa.gov/jpl/dawn/ceres-bright-spots-seen-closer-than-ever

"highly reflective material"- that doesn't sound like grey dust, Lajos. You keep forgetting/ignoring that they estimated an albedo of 0.4 with the spots not even resolved yet, so the actual albedo has to be much higher than that.

One can look up light curves for Ceres. It is reasonably variable, like 0.04 magnitudes or something like that. IF that 0.04 magnitude change is entirely due to the spots, we should be able to estimate their albedo from this variability, the albedo of the rest of the surface and now the known area of the spots.

How in the world could it be ice? Who knows. Maybe it really is salt or some kind of white clay or sand or something.

WHEN are we actually going to be able to know for sure what it is? CAN Dawn distinguish between salt and ice? Will we just get better and better pictures of it and but never be able to tell what it is? Don't they have some kind of neutron spectroscopy crap or something?

I suppose if its sublimating into space, you might be able to detect water vapor/oxygen/hydroxyl/hydrogen when you flew over the spots, but does Dawn even have instruments to detect that? Hopefully the other instruments on board aren't as weak as its visible light camera (the Fischer-Price plastic toy telescope I got for my fifth birthday has higher resolution...).

Ceres is well inside the frost line. Yes, that could be even ice, but what are the odds something impacted it very recently (few months at most)? They are pathetic, negligible.

I still think this is just bright ejecta. I'm trying not to think anthropocentric here, that's all.

cool!

BTW. Are there any colour pictures of Ceres? I mean pictures with natural colors (assumptions of what naked eye would have seen) not exxagerated to show some features.

Hubble made one but it's quite useless. Also I think NASA processed one Dawn made - dig through last 10-15 pages.

[winged]

Yes, I've found one :http://www.nasa.gov/jpl/dawns-ceres-color-map-reveals-surface-diversity

But those colours are exagerrated. I am looking for natural.

[lajoswinkler]

Exaggerated and false. That's NASA's PR right there.

[baggers]

Ceres is well inside the frost line. Yes, that could be even ice, but what are the odds something impacted it very recently (few months at most)? They are pathetic, negligible.

I still think this is just bright ejecta. I'm trying not to think anthropocentric here, that's all.

Earth and Moon are impacted very frequently, and Dawn is in the Asteroïd belt.

Last year:

http://www.space.com/24789-moon-meteorite-impact-brightest-lunar-explosion.html

1 year before, a 20 meter-diameter or 13.000 tons asteroïd in Tchebliabinsk, Russia.

http://en.wikipedia.org/wiki/Chelyabinsk_meteor

Edited May 22, 2015 by baggers

[lajoswinkler]

Doesn't matter. My point is that this is bright rocky ejecta. That can be thousands of years old. We're talking about geologically almost nonprocessed material. The Moon had its fair share of geology.

For this to be water ice it would have to be a very recent occurence and the odds of that happening on several places on Ceres are negligible.

[Kryten]

It could be ice if the protuberance is a cryovolcano, refreshing the surface every so often. If it is, we should catch signs of activity pretty soon.

[smjjames]

It could be ice if the protuberance is a cryovolcano, refreshing the surface every so often. If it is, we should catch signs of activity pretty soon.

'every so often' could be a really long time though.

[Newt]

The odds of some water eruption having hapened within about a year and a half are, about 100%. We actually saw this happen in multiple places on the surface in January 2014.

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[.]

(Link to ESA article)

[lajoswinkler]

But what could power this cryovolcanism? Ceres is not being tidally squeezed by anything, and it's very tiny therefore can't be very hot inside. I doubt it even has any decent stratification.

Uranium concentrates?

[baggers]

But what could power this cryovolcanism? Ceres is not being tidally squeezed by anything, and it's very tiny therefore can't be very hot inside. I doubt it even has any decent stratification.

Uranium concentrates?

We have evidence here on earth of "natural" local uranium concentrates and reaction that make a bit of warm (enought for boiling some water). So it's a possibility for a "local" Ceres cryovolcanism?

http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

The natural nuclear reactor formed when a uranium-rich mineral deposit became inundated with groundwater that acted as a neutron moderator, and a nuclear chain reaction took place. The heat generated from the nuclear fission caused the groundwater to boil away, which slowed or stopped the reaction. After cooling of the mineral deposit, the water returned and the reaction started again. These fission reactions were sustained for hundreds of thousands of years, until a chain reaction could no longer be supported.

We could even imagine that a local increase of uranium-ore concentration could be bring by (or started by) an asteroid impact? And start localy a chain reaction that last "hundreds of thousands of years" until all uranium is gone?

Edited May 23, 2015 by baggers

[Kryten]

Ceres is still a differentiated body, and cryovolcanism requires a lot less decay heat then conventional volcanism, so that seems a plausible mechanism to me.

We have evidence here on earth of "natural" local uranium concentrates and reaction that make a bit of warm (enought for boiling some water). So it's a possibility for a "local" Ceres cryovolcanism?

http://en.wikipedia.org/wiki/Natural_nuclear_fission_reactor

We could even imagine that a local increase of uranium-ore concentration could be bring by (or started by) an asteroid impact? And start localy a chain reaction that last "hundreds of thousands of years" until all uranium is gone?

Not possible; at this point in time, any uranium deposits have too much U-238 relative to -235 to sustain fission with light water. The natural reactors we've found were active over a billion years ago, when the proportion of -235 would've been much higher.

[baggers]

Not possible; at this point in time, any uranium deposits have too much U-238 relative to -235 to sustain fission with light water. The natural reactors we've found were active over a billion years ago, when the proportion of -235 would've been much higher.

Ceres as a different story (not well know) than earth: the "natural earth nuclear reactor" started to react at a precise moment in the earth story. (1.7 billons years ago) when some prerequisites meets locally.

[Kryten]

The ratio will be the same on Ceres and Earth at the same time, or indeed anywhere else in the solar system; it's been ticking ever since both uranium isotopes were produced by the supernova of a precursor to the sun. There's no natural mechanism that could heavily enrich a deposit in -235 after that.

[baggers]

The ratio will be the same on Ceres and Earth at the same time, or indeed anywhere else in the solar system; it's been ticking ever since both uranium isotopes were produced by the supernova of a precursor to the sun. There's no natural mechanism that could heavily enrich a deposit in -235 after that.

The global ratio U238/235, and the normal slow fission (half life of U238, that sort of things), yes.

but the chain reaction itself start only if and when certain local conditions meet.

[Kryten]

My point is the chain reaction is now impossible with natural materials. You need heavy water or extremely pure graphite for fission of natural uranium with the current ratio.

[Newt]

You might not need to get it to 0C and melt, if we assume that the water may have been mixed with some 'anti-freeze' materials. If the water has enough salt, or ammonia, or any of a host of other materials not implausibly present, there could probably be sufficient heat from pressure and radioactive decay to creat slush in the mantle.

Perhaps what we see in the spots is just a stain from some of these minerals falling back after an eruption of water. In this assumption, the water escaped, and it snowed salt, creating the spots.

[lajoswinkler]

If there is indeed cryovolcanism occuring, then the white deposit is salts. Ice simply can't survive there. It would have to be ejected as decent amounts of liquid water, not few kilogrammes as estimated and it would have to occur basically now, geologically speaking.

A very tenuous plume, carrying very small amount of very fine salty (doesn't have to be NaCl, of course) powder could be active every few decades.

Remember that this is an ancient, small body. It is not molten inside. Such time spans and such small amounts of higher albedo deposits means the depositions itself are very poor and very rare.

[Kryten]

You're talking as if the only possible heat source is retained heat, but we know this is a differentiated body with a metallic core. There will be significant decay heat.

[lajoswinkler]

Are you sure it is?

[Kryten]

It's certainly big enough, and Vesta was.

[-Velocity-]

It's certainly big enough, and Vesta was.

Vesta was- for the first couple million years or something like that. Then it froze out, because heat was escaping far faster than it was generated, and for like 99% of the solar system's history it's been geologically dead. Sure Ceres generates heat inside, who knows, it could even be producing MORE heat per unit volume in its core than Earth does (not that there's any reason to believe it is, but I suppose it's possible). The KEY difference is total surface area divided by total volume. Heat can only escape out of the surface. Per unit volume, Ceres has 13.3 times more surface area than Earth does. That means that whatever the residual decay heat it has simply escapes too fast to help maintain a molten core. Ceres certainly cannot have a molten core today, perhaps it did a long time ago, but that actually depends on how much of it is ice, I suppose. Ice doesn't have decay heat, which would also help contribute to an early death of internal-heat-driven geological activity on Ceres. If Ceres never got hot enough, it might not have even differentiated.

Also, I'd like to add that a lot of ice indicates that the body never went through a magma ocean period, further increasing the chance that Ceres never developed fully differentiated and molten core.

Edited May 23, 2015 by |Velocity|