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Aldebaran
Posted on: Feb 21 2021, 08:28 PM


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QUOTE (Blue Sky @ Feb 20 2021, 07:32 PM) *
I thought these tall rocks in the near distance in JRehling's photo were interesting. They seem different from their neighbors and the usual flat white rocks we see most places on Mars. Brought here in outflow from the delta?
[attachment=46960:Interesting_rocks.jpg]

Ejecta seems to be a more likely explanation. They are interesting though.
  Forum: Perseverance- Mars 2020 Rover · Post Preview: #249985 · Replies: 477 · Views: 232822

Aldebaran
Posted on: Jan 3 2019, 12:19 AM


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I wonder how much of it is water ice. It looks like a dirty snowball - or rather a dirty snowman.
  Forum: New Horizons · Post Preview: #243058 · Replies: 294 · Views: 477929

Aldebaran
Posted on: Jan 1 2019, 08:48 PM


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QUOTE (avisolo @ Jan 1 2019, 06:51 PM) *
Quick Crop:


Looks like a raw peanut in shape. How long before we know if the peanut is in one piece or broken?
  Forum: New Horizons · Post Preview: #242927 · Replies: 294 · Views: 477929

Aldebaran
Posted on: Jan 1 2019, 08:43 PM


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QUOTE (scalbers @ Jan 1 2019, 06:28 PM) *
The ground illumination should look like about 10 minutes after sunset on Earth.


That's not a useful analogy because it ranges from pitch black to daylight depending on season and latitude. It's more like a very dark rainy day.
  Forum: New Horizons · Post Preview: #242925 · Replies: 294 · Views: 477929

Aldebaran
Posted on: Jan 1 2019, 05:15 AM


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QUOTE (dtolman @ Dec 31 2018, 08:50 PM) *
Now that its shape is apparent, are there explanations left besides it tumbling so slowly that its not apparent in images?


Surrounded by millions of tiny orbiting particles
  Forum: New Horizons · Post Preview: #242879 · Replies: 294 · Views: 477929

Aldebaran
Posted on: Dec 30 2018, 10:56 PM


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QUOTE (Bjorn Jonsson @ Dec 30 2018, 11:25 PM) *
Interesting tidbit in the Spaceflight Now live-blog from Hal Weaver, there are some hints that Ultima Thule is a quickly-rotating object.


Could that explain the lack of light curve? (temporal resolution constraints)
  Forum: New Horizons · Post Preview: #242829 · Replies: 294 · Views: 477929

Aldebaran
Posted on: Jul 18 2015, 01:24 AM


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I feel like a kid at Christmas time eagerly awaiting the unwrapping of the presents.

Water ice "bedrock: has a density of 0.92, Nitrogen about 1.02 and frozen methane about 0.52. At Pluto's calculated maximum internal pressure, we can say with some confident that water ice would exist as orthorhombic Ice (XI) or possibly some hexagonal ice. There are no major consequences of phase transitions (under normal conditions).

It's not difficult to understand that frozen methane, which behaves like a glass at Plutonian temperatures, would tend to upwell if it ends up below the surface due to impacts, subduction etc.

It's question of how far out of the box you can reasonably think. As Nprev says, there is a vast amount of data yet to come which could change the way we look at Pluto very quickly. So much is tentative.
  Forum: Chit Chat · Post Preview: #224095 · Replies: 138 · Views: 86076

Aldebaran
Posted on: Jul 17 2015, 09:12 PM


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QUOTE (Nafnlaus @ Jul 17 2015, 08:57 PM) *
It's not silly at all - see my post above about eutectics. Especially if there's neon there (neon makes it almost too easy to have liquids at Pluto temperatures), but even if there's not. Examples:

* There's various mixtures of N2/CO/CH4/O2, without any neon, that have lower melting points than any of them have individually, including down to nearly 50K (Pluto is commonly said to get up to 55K)
* The temperature could easily get higher than the commonly cited temperature range for Pluto - that's based on very simplistic equilibrium-heating calculations. I'm sure the mission will give us far more accurate data on how hot Pluto actually gets - or at least, how hot it is right now.


They don't have to actually melt. Solid methane starts to get sticky and malleable at 50K. Think of the Earth's crust as an analogy.

link

Another thing to consider is large impacts. They will certainly cause localised melting and sublimation for a short time.

In terms of obliteration of surface features, the main consideration would be the sublimation and deposition process. Sublimation will take place wherever the partial pressure of that component is low enough, and will result in a localised drop in surface temperature wherever it is taking place. It's an endothermic process.

In situations where you have thin layers of surface ice on top of volatiles, that will reduce the sublimation and possibly result in highly viscous volatiles beneath the ice.

There is a good terrestrial analogy in the Antarctic Dry Valleys. Obviously, the sublimation of water is at a much higher temperature, and as long as the partial pressure of water is low enough in the "katabatic" winds, sublimation will occur.

Now depending on the exact circumstances, the katabatic wind may actually be close to its water dewpoint, but of course, the absolute humidity is extremely low. The rate of sublimation is determined by the wind velocity, temperature, water dewpoint of the katabatic wind and incident solar energy.

On Pluto, we already know that we have atmospheric nitrogen, and methane. Using the analogy, nitrogen is to the katabatic wind as methane is to ice.
  Forum: New Horizons · Post Preview: #224060 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 11:28 AM


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QUOTE (tfisher @ Jul 16 2015, 10:47 AM) *
Maybe solar heating together with precession of the polar axis can account for cracking. If there is a shift in the average insolation for the polar hemisphere due to that axis moving, thermal expansion at a hemisphere scale could be a powerful force.


I had the same thought. What I noticed was just how smooth (or reworked) the polar region is, but the high resolution images may totally change that initial impression. So I'll leave that comment in the parking lot for now.

What's next to be revealed? Cryovolcanic activity?
  Forum: New Horizons · Post Preview: #223744 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 10:17 AM


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QUOTE (Juramike @ Jul 15 2015, 03:06 PM) *
While a new thruster technology would be a welcome addition to the collective toolkit, for the purposes of this discussion we should limit it to proven and near-term available thrusters and technologies.


Fair enough, but it could turn out to be a huge game changer. I'll leave it at that.
  Forum: Exploration Strategy · Post Preview: #223737 · Replies: 24 · Views: 18970

Aldebaran
Posted on: Jul 16 2015, 09:48 AM


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QUOTE (nprev @ Jul 15 2015, 09:49 PM) *
Just finished the press conference. The biggest surprise by far seems to be that tidal heating is now quite obviously not the only possible means of internal heating for icy worlds.

There were hints of this from Enceladus, but I think that the general consensus was that it had to be tidal heating somehow. A paradigm falls.

Challenging assumptions to find the truth: That's the essence of science itself. smile.gif


I'd like to understand that conclusion better. The tidal forces on Triton from Neptune are in total about 20 times those on Pluto (please correct me if I'm wrong) from Charon, yet if you look at the dynamics, the forces are in a more concentrated band (angle) on Pluto compared to Triton. On average, Pluto actually has a higher temperature than Triton due to Triton's higher albedo. I'm looking forward to the temperature data, but current data has Pluto at 40 - 50K and Triton at about 35K.

Then again, Pluto has that 123 degree axial tilt, which means that the pole facing the sun gets much more insolation compared with Triton.

I can see that tidal heating is probably not the dominant factor on either body, but it probably remains as a factor. On the balance, Pluto "should be" more active than Triton .
  Forum: New Horizons · Post Preview: #223734 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 03:11 AM


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QUOTE (lars_J @ Jul 16 2015, 02:10 AM) *
True, but I'm merely questioning your assertion that the darker "mesa material" has to be much harder. If it was much harder, there would be mountains around that had eroded off into points or ridges - but I would think they would be far fewer as once the mesa is gone, erosion would accelerate. The but the very low number of "mesa mountains" in this image seems to imply (to me) that that top material is NOT much harder - if at all.

Otherwise I agree.


I agree that classical erosion may not be a dominant factor, or if it is, we need to be clear on the proposed mechanism.

From a sublimation point of view, the presence of contaminants that reduce the vapour pressure of any particular layer would increase the "hardness" or resilience to "erosion". We might have to rethink the term "hardness" in that context.
  Forum: New Horizons · Post Preview: #223710 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 02:59 AM


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QUOTE (Bill Harris @ Jul 16 2015, 01:08 AM) *
Yes.

And add into this mix lithologies composed of usual silicates, et al, with the addition of the unusual mineral oxidane, which will prove to have unusual properties under the cryogenic conditions on Pluto, especially in the presence of the typical suite of gas giant gases under cryogenic conditions.


I totally agree. We have a lot to learn about phase transitions of water ice mixtures,

It's interesting to regard water as a mineral series, the most extreme of which is metallic ice as found in the gas giants, but that's for another thread.
  Forum: New Horizons · Post Preview: #223708 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 12:50 AM


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QUOTE (nprev @ Jul 15 2015, 11:22 PM) *
Spectacular, John.

That black smudge is smack dab on top of an elevated 'ropy' looking region, very different from the surrounding plains & peaks. That is very, very intriguing.


Just a thought, but I can't help think in terms of the Antarctic dry valleys as a kind of water ice sublimation analogy. So will areas of higher ablation have a darker colour due to a gradual concentration of non volatiles?

If we think about the sublimation process, maybe some tholin powder is being continually (seasonally/diurnally) entrained into the released gas, but the volatiles emission will be the dominant process. The resultant nitrogen snow will fall in areas of predominant deposition which may be lighter in colour.
  Forum: New Horizons · Post Preview: #223691 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 16 2015, 12:16 AM


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QUOTE (Habukaz @ Jul 15 2015, 09:38 PM) *
My interpretation of a north polar depression on Charon:

[attachment=36948:Charon_n...pression.gif]


My thoughts are that it also coincides with the area of highest levels of insolation. The pole is constantly exposed to the sun. Maybe there is a connection there? Higher ablation/sublimation rates perhaps?
  Forum: New Horizons · Post Preview: #223685 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 11:55 PM


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I think that one of the keys to understanding this terrain is understanding the physical properties of the various volatiles that dominate the surface and crust of Pluto. So:

Pluto Surface temperature range: 40-50K. Hopefully we'll get more detailed information on temperature distribution from the NH datasets.

We know that nitrogen will potentially liquefy at about 63K depending on pressure. This is more likely at depth where no boiling/ sublimation can occur. Sublimation will result in rapid heat loss and solidification on the surface.

Solid methane starts to get malleable and sticky at around 50K to 90K, so it may be largely responsible for a lot of the surface reworking, and it may be a seasonal effect.

There is also this paper on the rheology of solid nitrogen and methane:

link

Some other (rhetorical) questions arise with regard to the relative densities of the volatile components. How do they change within the temperature range found on the surface of Pluto?

The geology of Pluto is obviously pretty complex.

What are the possible stable mixtures? For example, are there methane hydrates/ clathrates.
  Forum: New Horizons · Post Preview: #223681 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 08:51 PM


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Just woke up. (damn I missed the press conference.) Total information overload. Some incredible images/

QUOTE (Marvin @ Jul 15 2015, 09:06 PM) *
So I've heard three possible sources of heat driving the geology (or a combination of them):

1. Radioisotopes
2. Liquid water still releasing heat from the original formation
3. Impact Event with Charon


4. Insolation

- and I'd be guessing, but volume changes associated with phase transitions in water ice. Possibly Ice XI to Ice IX (at depth of course)
  Forum: New Horizons · Post Preview: #223630 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 07:25 AM


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Now we need to develop propulsion systems that use practically no propellant. Only recently, the idea was regarded as controversial, but the RF resonant cavity thruster is starting to look promising. (or at least not impossible)
http://ntrs.nasa.gov/search.jsp?R=20140006052
  Forum: Exploration Strategy · Post Preview: #223479 · Replies: 24 · Views: 18970

Aldebaran
Posted on: Jul 15 2015, 02:10 AM


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Loved that question from the Pluto kid. "What is the objective of the extended mission?" smile.gif Much more intelligent than some questions from the general press.
  Forum: New Horizons · Post Preview: #223456 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 01:07 AM


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QUOTE (nprev @ Jul 15 2015, 01:02 AM) *
I'm a bit overwhelmed. Cannot overstate congratulations to Alan and the entire New Horizons team. What an astonishing feat of technology and bold exploration!!!!


Absolutely, and they are going to be busy over the next 16 months. Can't wait to read the papers that come out of this epic project.
  Forum: New Horizons · Post Preview: #223431 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 01:00 AM


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QUOTE (nprev @ Jul 15 2015, 12:56 AM) *
CNDH reports expected amount of data collected.



Looking good. I wonder if Alice expected to be in the public spotlight so much.
  Forum: New Horizons · Post Preview: #223426 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 15 2015, 12:29 AM


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QUOTE (MahFL @ Jul 15 2015, 12:21 AM) *
She said the phone home signal will indicate which sequences ran ok, whether there had been any computer resets and the amount of the recorder used.


It was mentioned during one of the news feeds that 8Gb (2 x 4Gb) of memory had been filled following the last transmission.
  Forum: New Horizons · Post Preview: #223411 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 14 2015, 09:53 PM


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QUOTE (Daniele_bianchino_Italy @ Jul 14 2015, 10:43 PM) *
Possible images of stige and cerber0 moons?
And possible a more dense atmosphere and pressure and surface liquid material in other time of pluto year?


The orbit ranges from about 30AU to about 49AU. We're currently at 33AU, so much closer to the perihelion than the aphelion. I tend to think that in terms of densest atmosphere, we are pretty close to that phase now.
  Forum: New Horizons · Post Preview: #223380 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 14 2015, 07:27 PM


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QUOTE (craigmcg @ Jul 14 2015, 12:03 PM) *
Anyone else wish that we could have heard what the speakers were saying instead of that NASA media guy telling how exciting it was?



I was half expecting somebody to come up to him and say shhh! The part where they all waved their little flags was somewhat surreal too, However, nothing can detract from this occasion and the success of the mission.
  Forum: New Horizons · Post Preview: #223347 · Replies: 1286 · Views: 6817674

Aldebaran
Posted on: Jul 14 2015, 11:35 AM


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QUOTE (Mercure @ Jul 14 2015, 12:31 PM) *
That's the Kodak moment right there, the image that will be on all the front pages tomorrow, and what a fantastic shot it is, great angle with the white area surrounded by all sorts of darker hues and shapes. Congratulations to NASA, the NH team, the US and all of us here on planet Earth: we finally had a look at all of our neighbourhood!



It will be good to see the first high resolution MVIC picture.
  Forum: New Horizons · Post Preview: #223222 · Replies: 1286 · Views: 6817674

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