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.