Extreme Negative Polarization (peer reviewed Astrophysical Journal)

[Julian_M]

https://iopscience.iop.org/article/10.3847/2041-8213/ae0c08

https://iopscience.iop.org/article/10.3847/2041-8213/ae0c08/pdf

Above is peer reviewed article from The Astrophysical Journal Letters concerning "Extreme Negative Polarization of New Interstellar Comet 3I/ATLAS"

What is really the meaning of extreme negative polarization using the polarized sunglasses as analogy? Ever since last year I couldn't understand the meaning of extreme negative polarization about 3i/Atlas.

from the peer reviewed article above:

"We present the first polarimetric observations of the third discovered interstellar object, 3I/ATLAS (C/2025 N1), obtained pre-perihelion with FORS2/VLT, ALFOSC/NOT, and FoReRo2/RCC, over a phase angle range of 7.7-22.4°. This marks the second ever polarimetric study of an interstellar object, the first distinguishing 2I/Borisov from most Solar System comets by its higher positive polarisation. Our polarimetric measurements as a function of phase angle reveal that 3I is characterised by an deep and narrow negative polarisation branch, reaching a minimum value of -2.7% at phase angle 7°, and an inversion angle of 17° -- a combination unprecedented among asteroids and comets, including 2I/Borisov."

I googled a lot about it but managed to find a few illustrations only

To aid in understanding. About the paper description "reaching a minimum value of -2.7% at phase angle 7°, and an inversion angle of 17°". What is the minimum value, phase angle and inversion angle of a pair polarized sunglasses? I only know 90 degrees vertical and horizontal polarization description.

Also polarized sunglasses are dimmer because the other 90 degree is filtered. In the case of 3i/Atlas. Does it mean it looks dimmer because some polarization is shifted in angle very steep 2.7% like the 90 degree horizontal polarization being filtered in sunglasses?

 

[A.T.]

What is really the meaning of extreme negative polarization ...

It's explained in the paper you linked:

The degree of linear polarization Pr of sunlight scattered by cometary dust particles is measured as the difference between the fluxes perpendicular and parallel to the scattering plane (Sun–comet–observer plane), normalized by their sum, and is highly sensitive to the solar phase angle α (Sun–comet–observer angle). Because of this definition, polarization is positive when the polarization direction is oriented perpendicular to the scattering plane, and negative when parallel.

... using the polarized sunglasses as analogy?

Polarized sunglasses do not generate polarization by scattering, so you cannot apply the above defintion to them.

 

[Ibix]

Light reflecting off any surface is usually partially polarised, either parallel or perpendicular to the scattering plane (the flat plane defined by the sun, the comet, and the camera). Negative polarisation means it's parallel to the plane, positive means perpendicular. The underlying cause is that how strong a reflection is depends on the angle of incidence of the light, but it depends differently for the polarisation parallel and perpendicular to the surface. So you get a changing mix of polarisations as the angle of the reflection varies.

So all the graph is showing you is how much difference in brightness you see when you put a polarising sheet in front of your camera parallel and perpendicular to the scattering plane, and how that varies as the phase angle (which I believe is the angle between the direction of travel of the incident and reflected light) varies. "Inversion angle" is the angle at which the polarisation sign switches. It's also very weakly polarised - less than 3% difference in the parallel and perpendicular fluxes.

The result tells you something about the surface roughness (for example, Titan does not have the negative polarisation dip that all other moons have because it has a thick atmosphere that reflects light, rather than a rocky surface), but you'd need to know more about polarimetry than I do to say anything helpful.

 

[Julian_M]

Light reflecting off any surface is usually partially polarised, either parallel or perpendicular to the scattering plane (the flat plane defined by the sun, the comet, and the camera). Negative polarisation means it's parallel to the plane, positive means perpendicular. The underlying cause is that how strong a reflection is depends on the angle of incidence of the light, but it depends differently for the polarisation parallel and perpendicular to the surface. So you get a changing mix of polarisations as the angle of the reflection varies.

So all the graph is showing you is how much difference in brightness you see when you put a polarising sheet in front of your camera parallel and perpendicular to the scattering plane, and how that varies as the phase angle (which I believe is the angle between the direction of travel of the incident and reflected light) varies. "Inversion angle" is the angle at which the polarisation sign switches. It's also very weakly polarised - less than 3% difference in the parallel and perpendicular fluxes.

The result tells you something about the surface roughness (for example, Titan does not have the negative polarisation dip that all other moons have because it has a thick atmosphere that reflects light, rather than a rocky surface), but you'd need to know more about polarimetry than I do to say anything helpful.

Thanks. An example to determine if I got the idea. Supposed I have a truck that is light green in color. And supposed it has special adjustable surface metamaterial that you can tune the polarization to different values. If I create same setting as 3i/Atlas. Would the truck still be light green in color or would it change to other color? What color would it change to? Or can I make it same polarization as 3i/Atlas but still light green in color?

 

[Ibix]

Thanks. An example to determine if I got the idea. Supposed I have a truck that is light green in color. And supposed it has special adjustable surface metamaterial that you can tune the polarization to different values. If I create same setting as 3i/Atlas. Would the truck still be light green in color or would it change to other color? What color would it change to? Or can I make it same polarization as 3i/Atlas but still light green in color?

That would depend on the properties of your magic coating, so it's unanswerable. Generally speaking, adding random scifi elements to a scenario does not help understanding of science.

 

[Julian_M]

That would depend on the properties of your magic coating, so it's unanswerable. Generally speaking, adding random scifi elements to a scenario does not help understanding of science.

I tried to google illustrations about extreme negative polarizations. I couldn't find one where it is illustrated fully. I found one of these in the few images.

Let us go to the typical polarization example for my questions:

When you mentioned "scattering plane". It is like the above plane of the source at left, correct? Now if extreme negative polarization means the light travels parallel to the scattering plane.. and I drew the blue waves depicting it. How can the light wave parallel to the source plane travels to the center. Does it? And does it mean all the light 100% is in the parallel plane?

If it does. Let's say the middle polarization filter doesn't allow any vertical component but only allow light parallel to the scattering plane (the blue) and the blue travels to the right. How can you see the light travelling parallel to the plane? Please draw visualization aid if you can because there is none in the entire internet. Many thanks.

 

[berkeman]

Above is peer reviewed article from The Astrophysical Journal Letters concerning "Extreme Negative Polarization of New Interstellar Comet 3I/ATLAS"

@Julian_M -- It seems from your recent thread starts that you are obsessed with proving that 3I/ATLAS is an alien-made object. That will not go over very well here (as you can tell from your recent infraction). If that is your goal, please stop posting about this. If it is not, please state *very clearly* what your goal is in starting these threads. Short leash...

 

[Julian_M]

View attachment 369448

@Julian_M -- It seems from your recent thread starts that you are obsessed with proving that 3I/ATLAS is an alien-made object. That will not go over very well here (as you can tell from your recent infraction). If that is your goal, please stop posting about this. If it is not, please state *very clearly* what your goal is in starting these threads. Short leash...

My goal is to learn the actual physics and technical stuff so i can prove it is natural object. Because so many ignorant out there who are not familiar with technical stuff so they are swayed otherwise especially knowing the universe is so old and our solar system so young so there should be many before us . By knowing the technical stuff of it all. One can see through them and know it is natural. I'd like to share what I learnt to the 100,000 ignorant who were swayed by it. So I need to understand the basic. But my posts are not 3i/Atlas only of course. By March 16 after it reached Jupiter Hill Radius and no probes deployed to one of the moons to build outpost. People would know it is all rubbish and I'd want to explain why it is so by knowing the facts like how exactly extreme negative polarization means. Does it mean only half or fractions of the light rays are parallel to the scattering plane. Or 100%. I want to know up to this details only, so have rough idea. I'd NOT start new thread about 3i/Atlas.

 

[berkeman]

My goal is to learn the actual physics and technical stuff so i can prove it is natural object.

That is a good thing; thank you for clarifying.

One can see through them and know it is natural. I'd like to share what I learnt to the 100,000 ignorant who were swayed by it.

Well, that's also probably a good thing, but please keep in mind that we don't debunk pseudoscience claims here.

By March 16 after it reached Jupiter Hill Radius and no probes deployed to one of the moons to build outpost.

I have no idea what you mean by that.

 

[A.T.]

I tried to google illustrations about extreme negative polarizations.

It's described in the paper you linked. If you don't understand that description, google the terms used in it, like 'scattering plane' and 'phase angle'. It should bring up images like this one:

From Fig 1 of: https://www.nao.ac.jp/en/contents/news/topics/2018/20180910-50cm-phaethon-authors-en.pdf

 

[Ibix]

It's also worth noting that the polarimetry measures seem to be averages over the region shown in the images in figure 2 in the paper linked in the OP. They have a diameter of ~40,000km. So I think this is polarimetry of the dust cloud, not the surface of the comet.

 

[Ibix]

Incidentally, this is a nice demo of polarisation in scattering.

It isn't quite what's going on in the comet case, because he uses a polarising film before the scattering to show that it's only one polarisation that's scattered, whereas the astronomical observation puts the polarising film after the scattering to see what's been scattered. And the polarisation percentage is much, much higher. Also, it's Rayleigh scattering whereas I suspect the comet's halo is causing Mie scattering. But it's a related effect.

 

[Julian_M]

It's also worth noting that the polarimetry measures seem to be averages over the region shown in the images in figure 2 in the paper linked in the OP. They have a diameter of ~40,000km. So I think this is polarimetry of the dust cloud, not the surface of the comet.

Speaking of dust clouds. Anyone got idea why 3i/atlas doesn't contain any fine dusts but only millimeters to 1/10th of meter (4 inches) sized dusts as reported by a peer reviewed paper by the American Astronomical Society. How can outgassing occur witnout any fine dusts?

https://iopscience.iop.org/article/10.3847/2515-5172/ae3f95/ampdf

Here is relevant passage:

"Some tension exists because the gas production of 3I had been shown to be dominated by icy coma dust grains in SPHEREx August-2025 pre-perihelion imaging (Lisse+2025a,b), and these “grains” would have had to have been >10m thick to preserve deep unprocessed material. This would imply a huge amount of coma dust mass, because these same large boulders have to provide enough surface area to make the coma ~100x brighter than the nucleus in reflected sunlight. On the other hand, we know the coma grains must be large (mm to dm, at least) because there is no evidence for a radiation pressure dominated anti-solar dust tail."

Here is the imaging result in the same peer reviewed paper:

"3. Imaging Results. The gas-comae detected by SPHEREx were all resolved, extending from 1’-to-3’ in radius (Figure 1), and all except the CN and C-H organics comae are markedly round with respect to the Sun and orbital velocity directions. By contrast, the SPHEREx continuum dust and organics images are markedly pear-shaped, with the “pear-stem” pointing sunward. The very different morphologies suggest that CN, C-H, and H2O are sourced from the dust, while the CO2, and CO-gas is from a symmetric region centered on the nucleus. No obvious jet or small-particle dominated anti-solar tail structures were found."

This is an artist rendition of it:

It doesn't appear like a normal comet which has dust tail like the following as the paper also emphasized at end of sentence in my first quote above.

In the following illustration with descriptions, the sun is on right side.

Normal comet has anti-solar normal tail due to the solar wind pushing it. But in 3i/Atlas, the 4 inches dusts form the anti-tail and the solar wind can't push them because they are big. The anti-tail extends 1/3 the distance to the moon as shown in all Hubble images. If you will read article like from space dot com they never mentioned this anomaly that the peer reviewed journal American Astronomical Society mentioned.
If you will say to refer to last paragraph of the article where amorphous carbon- and olivine-rich dust were mentioned. They are sub-micron size and the not the millimeter to decimeter minimum size the article mentioned.

Googling size of them:
"Amorphous carbon dust particles typically range from about 10 nm (nanometers) to a few micrometers (µm). Typical Size Range: Olivine grains in cosmic dust also tend to vary widely, with typical sizes ranging from sub-micron (~10 nm) up to several microns". These are not the millimeter to decimeter (4 inches) minimum sized mention in the peer reviewed paper.

The following is the frustrations expressed by people about it which mentions directly the article. Please, I include this so you will know the facts that the media won't even report. So please address it directly instead of just deleting this. Why doesn't 3i/Atlas emit any fine dusts?



He is addressing the peer reviewed paper I mentioned directly and the concerns all media ignore (due to ignorance). So please address directly his and others concerns how can outgassing occurs without any fine dusts (as mentioned in the peer reviewed paper) instead of just deleting it and just ignoring and shoving aside this valid major astronomical puzzle. You may delete it saying it is not valid reference. But I mentioned the valid peer reviewed reference and the video is just describing about it and the truth and frustrations why media won't report it.