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mnemeth
2010-Nov-05, 12:51 AM
I have a problem with the images returned by the EPOXI mission fly-by of Hartley 2.

In the images, it appears to me that the so-called "dust jets" emanating from comet Hartley 2 are luminous.

As the comet rotates, the jets exhibit clear luminosity in the dark side of the comet. They are far far too bright to be simple dust jets.

http://abcnews.go.com/images/Technology/ht_hartley_101104_main.jpg

Does anyone else find the apparent luminosity of the jets in the dark side of the comet odd?

There are several pictures where the jet is clearly in the shadows yet it glows like a plasma discharge.

In the close ups you can see fine collimated jets emanating from bright point sources in the dark side of the comet.

Swift
2010-Nov-05, 03:24 AM
In the images, it appears to me that the so-called "dust jets" emanating from comet Hartley 2 are luminous.

As the comet rotates, the jets exhibit clear luminosity in the dark side of the comet. They are far far too bright to be simple dust jets.

Hi mnemeth, welcome to BAUT.

I suspect that the material of the jets is much better at scattering light from the sun than body of the comet itself. Part of that may be the particle size, part of that may be the composition - they may not be simple dust, but may be ice or contain ice crystals.

It is a little hard for me to get the perspective, but I suspect the jets become illuminated once they leave the shadow of the comet.

mnemeth
2010-Nov-05, 03:51 AM
Yeah, you'd think that should be the case.

However, I can see the clear edge of rock cutting off the discharge jet.

So it has to be that the discharge is behind the rock that's jutting out.

Which would have to mean the jet itself is luminous.

http://fascistsoup.com/wp-content/uploads/2010/11/hartley11.jpg

http://fascistsoup.com/wp-content/uploads/2010/11/hartley2.jpg

korjik
2010-Nov-05, 04:25 AM
I have a problem with the images returned by the EPOXI mission fly-by of Hartley 2.

In the images, it appears to me that the so-called "dust jets" emanating from comet Hartley 2 are luminous.

As the comet rotates, the jets exhibit clear luminosity in the dark side of the comet. They are far far too bright to be simple dust jets.

http://abcnews.go.com/images/Technology/ht_hartley_101104_main.jpg

Does anyone else find the apparent luminosity of the jets in the dark side of the comet odd?

There are several pictures where the jet is clearly in the shadows yet it glows like a plasma discharge.

In the close ups you can see fine collimated jets emanating from bright point sources in the dark side of the comet.

You can get that all off of a couple overexposed black and white images? Black and white images that are overexposed maybe to show something like jets?

tusenfem
2010-Nov-05, 08:10 AM
Welcome to BAUT, mnemeth

The jets are much much better at scattering sunlight than the surface of the comet itself.
However, as we want to see details of the surface of the comet, that means that we have to overexpose the bright parts of the image, which would be the jets.
No, the jets are not "self luminous," they are not "plasma discharges."


Just a reminder to all, any discussion of an "electric comet" model is considered ATM.

astromark
2010-Nov-05, 08:23 AM
Swift has presented a good argument... That the image is over exposed to reveal detail of the comet...

The brightness of the jets is because of the fine material and ices reflect light more effectively than the dark body comet...

Hornblower
2010-Nov-05, 01:25 PM
Yeah, you'd think that should be the case.

However, I can see the clear edge of rock cutting off the discharge jet.

So it has to be that the discharge is behind the rock that's jutting out.

Which would have to mean the jet itself is luminous.

http://fascistsoup.com/wp-content/uploads/2010/11/hartley11.jpg

http://fascistsoup.com/wp-content/uploads/2010/11/hartley2.jpg

I think you are misjudging the orientation of the shadow. The appearance of the bright side of the nucleus tells me the shadow is extending to the left and away from us, not straight down. The jets on the lower left appear to be coming from hot spots just over the terminator, and they are sticking up into sunlight just as a high mountain just past the terminator on the Moon does. My educated guess is that those hot spots had been baking in full sunlight for several hours, and that the rotation of the comet had carried them just past the terminator just before the photo was taken.

antoniseb
2010-Nov-05, 01:40 PM
Which would have to mean the jet itself is luminous.
http://fascistsoup.com/wp-content/uploads/2010/11/hartley11.jpg


Fascist Soup is kind of an odd website to be coming here from.
Looking at other shots from the fly-by, where the sun angle is not from straight behind the space-craft, it appears to my unprofessional eye that there are jets invisible because of shadow, until they get some distance away from the nucleus of Hartley 2.

mnemeth
2010-Nov-05, 02:26 PM
Welcome to BAUT, mnemeth

The jets are much much better at scattering sunlight than the surface of the comet itself.
However, as we want to see details of the surface of the comet, that means that we have to overexpose the bright parts of the image, which would be the jets.
No, the jets are not "self luminous," they are not "plasma discharges."


I understand the exposure times involved, but I also understand that jets in deep space must have a light source to be visible.

We can see the main discharge area lit up like a Christmas tree - it's blazing white. If that is all from sun light, I don't understand why the rest of the comet surface is not similarly "over-exposed." There should be little difference between the source points and the rest of the surface in terms of brightness.

But it's the bottom of the comet where, to me, I clearly see the jets as being lit up but in the shadow of the comet.

No scattering could generate that kind of apparent brightness without also lighting up the bottom of the comet.

The only conclusion that I can draw from this is that the jets themselves are luminous.

Hungry4info
2010-Nov-05, 02:36 PM
Don't forget we see something similar to this on Enceladus's plumes.
e.g. here http://apod.nasa.gov/apod/image/0911/enceladus12_cassini_big.png
Orientation of the parent body's shadow is more than enough to explain what we see in both cases.

mnemeth
2010-Nov-05, 02:41 PM
Don't forget we see something similar to this on Enceladus's plumes.
e.g. here http://apod.nasa.gov/apod/image/0911/enceladus12_cassini_big.png
Orientation of the parent body's shadow is more than enough to explain what we see in both cases.

That picture of Enceladus looks very much like an aurora discharge on earth.

I don't see why they couldn't be the exact same effect.

Strange
2010-Nov-05, 03:41 PM
That picture of Enceladus looks very much like an aurora discharge on earth.

I don't see why they couldn't be the exact same effect.

Well, I guess appearnces can be deceiving. Analysis of the plumes shows them to be salt water rich in carbonates and other orgnaic compounds.

Swift
2010-Nov-05, 03:46 PM
We can see the main discharge area lit up like a Christmas tree - it's blazing white. If that is all from sun light, I don't understand why the rest of the comet surface is not similarly "over-exposed." There should be little difference between the source points and the rest of the surface in terms of brightness.

No, you would expect that the sources of the jets would be much brighter than the rest of the comet.

The best understanding of a comet is that it is basically a very dirty snowball, an inhomogenous mixture of ice, gas, organics, and minerals. This mixture would generally have a dark color. For example, the organic components would turn dark over time from UV exposure and other types of weathering.

I suspect the sources of the jets are spots that for whatever reason, expel more volatile materials (water and gas). They may have higher concentrations of gas or water, or they may have absorbed more energy because of their darkness or the local topography. But once they start venting, the venting will expose fresh material, which will have a much lighter color.

mnemeth
2010-Nov-05, 04:16 PM
Well, I guess appearnces can be deceiving. Analysis of the plumes shows them to be salt water rich in carbonates and other orgnaic compounds.

From what I understand, analysis shows ions of water, which doesn't really demonstrate anything contrary to what one would expect from the spectra of an aurora.

Swift
2010-Nov-05, 05:13 PM
Just a reminder to all, any discussion of an "electric comet" model is considered ATM.

Now, I'm going to put my moderator hat on...

mnemeth, you are getting very close to advocating a non-mainstream opinion. Q&A is for asking questions and receiving mainstream answers to them. You can ask follow-up questions, but you can not challenge the mainstream answer in Q&A. If you wish to advocate a non-mainstream interpretation of these pictures (or any other topic) you must do it in the Against The Mainstream (ATM) section of this forum.

And if you are going to advocate an "Electric Universe" idea, I warn you that we have been there far too many times and you will be aggressively challenged on those ideas.

PetersCreek
2010-Nov-05, 05:51 PM
mnemeth banned as a sock puppet of a previously banned user. Since the OP "question" has been adequately answered, this thread is closed.