Crescent Neptune and Triton (2009 Dec 13)

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Crescent Neptune and Triton (2009 Dec 13)

Post by APOD Robot » Sun Dec 13, 2009 4:56 am

Image Crescent Neptune and Triton

Explanation: Gliding silently through the outer Solar System, the Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase in 1989. The above picture of the gas giant planet and its cloudy moon was taken from behind just after closest approach. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth. The unusual vantage point also robs Neptune of its familiar blue hue, as sunlight seen from here is scattered forward, and so is reddened like the setting Sun. Neptune is smaller but more massive than Uranus, has several dark rings, and emits more light than it receives from the Sun.


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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by orin stepanek » Sun Dec 13, 2009 5:01 am

and emits more light than it receives from the Sun.
I wasn't aware of this. What would cause it to do this? Is Neptune a hot body?

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by geckzilla » Sun Dec 13, 2009 5:11 am

I'm stealing Art's job for a moment. Here you go, Orin. :)
http://en.wikipedia.org/wiki/Neptune#Internal_heat wrote: Neptune's more varied weather when compared to Uranus is believed to be due in part to its higher internal heat. Although Neptune lies half again as far from the Sun as Uranus, and receives only 40% its amount of sunlight, the two planets' surface temperatures are roughly equal. The upper regions of Neptune's troposphere reach a low temperature of −221.4 °C (51.7 K). At a depth where the atmospheric pressure equals 1 bar (100 kPa), the temperature is −201.15 °C (72.0 K). Deeper inside the layers of gas, however, the temperature rises steadily. As with Uranus, the source of this heating is unknown, but the discrepancy is larger: Uranus only radiates 1.1 times as much energy as it receives from the Sun; while Neptune radiates about 2.61 times as much energy as it receives from the Sun. Neptune is the farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System. Several possible explanations have been suggested, including radiogenic heating from the planet's core, conversion of methane under high pressure into hydrogen, diamond and longer hydrocarbons (the hydrogen and diamond would then rise and sink, respectively, releasing gravitational potential energy), and convection in the lower atmosphere that causes gravity waves to break above the tropopause.
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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by orin stepanek » Sun Dec 13, 2009 2:17 pm

10-Q. But still not enough of its own light to prevent the crescent. 8-)

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by Chris Peterson » Sun Dec 13, 2009 3:54 pm

orin stepanek wrote:10-Q. But still not enough of its own light to prevent the crescent. 8-)
"Energy" is probably a better word than "light". The excess energy from Neptune is very long wavelength- far outside of what we typically call light.

Over long time spans, even the Earth radiates more energy than it receives from the Sun, although the difference is incredibly slight. Currently we are radiating less than we receive, which is why the global temperature is rising.
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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by neufer » Sun Dec 13, 2009 6:09 pm

Chris Peterson wrote:
orin stepanek wrote:10-Q. But still not enough of its own light to prevent the crescent. 8-)
"Energy" is probably a better word than "light". The excess energy from Neptune is very long wavelength- far outside of what we typically call light.

Over long time spans, even the Earth radiates more energy than it receives from the Sun, although the difference is incredibly slight. Currently we are radiating less than we receive, which is why the global temperature is rising.
With 12 longwave (~250K) photons going out in 12 different random directions
for each (~6000K) shortwave photon coming from the sun's narrow direction
we do not import energy...rather we export entropy.

I find that a fascinating concept to contemplate.
  • ----------------------------------
    GEORGE: (after a moment's thought) Art Vandelay.

    ELAINE: (incredulity) Art Vandelay? This is my boyfriend?

    GEORGE: That's your boyfriend.

    ELAINE: What does he do?

    GEORGE: He's an importer.

    ELAINE: Just imports? No exports?

    GEORGE: (getting irritated) He's an importer-exporter. Okay?

    ELAINE: Okay. So, I'm dating Art Vandelay. What is the problem we're discussing?

    Elaine and George go into another bout of deep thought.

    ELAINE: Ah! (explaining, with hand gestures) How 'bout this? How about, he's
    thinking of quitting the exporting, and just focussing in on the importing. And
    this is causing a problem, because, why not do both?
    ----------------------------------
Art Vandelay

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by orin stepanek » Sun Dec 13, 2009 11:57 pm

Chris Peterson wrote:
orin stepanek wrote:10-Q. But still not enough of its own light to prevent the crescent. 8-)
"Energy" is probably a better word than "light". The excess energy from Neptune is very long wavelength- far outside of what we typically call light.

Over long time spans, even the Earth radiates more energy than it receives from the Sun, although the difference is incredibly slight. Currently we are radiating less than we receive, which is why the global temperature is rising.
Thanks; quite interesting! :) I knew Jupiter emitted energy; http://burro.astr.cwru.edu/stu/advanced/jupiter.html but I was unaware of the other gas giants. I can see that it would be reasonable though. :o

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by Jallen127 » Mon Dec 14, 2009 2:04 am

Regarding Neptune being a "hot body," what intrigues me about the photo is the plume on the crescent edge. It is barely visible at about the "9:30" position. Has this been identified? The plume has a loop appearance, much like solar flares on the sun. However, should any heat generating activity be happening, one would think that, even though it may not be in the visible spectrum, that one or more of the various " ****ometers " aboard Voyager 2 would have detected the emitted energy from the dark side of the planet. This could also be an impact site, or an artifact. Voyager missions discovered volcanic plumes rising 8 km above the surface of Triton, but I have been unable to find info on plumes rising from the surface of Neptune.

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by orin stepanek » Mon Dec 14, 2009 2:52 am

I really looked; but I don't see any plume at the crescent edge. I even magnified the photo up to 400%. I must be missing it. :?

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by geckzilla » Mon Dec 14, 2009 3:09 am

If you mess with the gamma on the image it's a lot easier to see. I edited the pic and drew boxes around the "plumes" ... Triton apparently has one, too. I have to wonder how many generations of jpeg artifacting are affecting the image.
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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by orin stepanek » Mon Dec 14, 2009 3:24 am

10-Q It's pretty clear on your illustration. I still can't find it on the original. Why would Neptune have a plume? It's a gas giant. I would think it to be some artifact! :?

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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by Chris Peterson » Mon Dec 14, 2009 4:31 am

orin stepanek wrote:10-Q It's pretty clear on your illustration. I still can't find it on the original. Why would Neptune have a plume? It's a gas giant. I would think it to be some artifact! :?
Almost certainly an artifact. Probably some sort of pixel defect smeared out by JPEG processing. There seem to be quite a few similar artifacts across the image. I could believe a moon having a plume, but there's no mechanism for a gas giant having one (other than an impact).
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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by geckzilla » Mon Dec 14, 2009 3:32 pm

For some reason I was thinking about this last night before falling asleep and an idea about the two artifacts came up. Perhaps someone was cleaning up the image to get rid of such defects, maybe even with an automatic noise reduction filter, but since those two happened to be touching the very edge of the crescents they were in a masked off zone that did not receive any treatment.
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Re: Crescent Neptune and Triton (2009 Dec 13)

Post by neufer » Mon Dec 14, 2009 5:07 pm

Jallen127 wrote: what intrigues me about the photo is the plume on the crescent edge. It is barely visible at about the "9:30" position. Has this been identified?
Could it be dark Proteus :?:

Code: Select all

Moon      Albedo    Radius   Semi-major axis
------------------------------------------------------
Triton 	0.760 	1353 km    355,000 km
Proteus   0.096     210 km    118,000 km
Art Neuendorffer